The Effects of Road Noise on Pacific Chorus Frog Communication

______________________________________________________

AN ABSTRACT OF THE THESIS OF

Danielle V Nelson for the degree of Master of Science in Forest Ecosystems and Society

presented on December 7 2015

Title The Effects of Road Noise on Pacific Chorus Frog Communication

Abstract approved

Tiffany S Garcia

Amphibians are experiencing global population declines and are one of the most

threatened groups of vertebrates This can be attributed to multiple environmental

stressors such as habitat loss disease invasive species and climate change For vocal

amphibian species loss of acoustic habitat due to anthropogenic noise may be yet another

environmental stressor The Pacific chorus frog (Pseudacris regilla) is the most common

vocal species of the Pacific Northwest It is described as a generalist that can occupy

human-dominated habitat types including agricultural and urban wetlands As such this

species is exposed to anthropogenic noise which can interfere with vocalizations during

the breeding season We hypothesized that Pacific chorus frogs would alter the spatial

and temporal structure of their breeding vocalizations to accommodate a widespread

anthropogenic stressor road noise We compared Pacific chorus frog call structure and

ambient road noise levels at 8 sites along a gradient of noise exposures in the Willamette

Valley Oregon USA We used both passive acoustic monitoring and directional

recordings to determine source level (ie amplitude or volume) dominant frequency (ie

pitch) call duration and call rate of individual frogs and to quantify ambient road noise

levels We found that Pacific chorus frogs significantly reduced their call rate at relatively

higher levels of ambient road noise leading to a reduction in the amount of total time

spent calling We found no other changes to call structure (eg frequency and duration)

The absence of additional call structure changes to mediate the impact of road noise

resulted in a drastic reduction in the active call space of an individual frog Coupled with

the decrease in call rate this signifies that communication is significantly reduced both

spatially and temporally This may have implications for the reproductive success of this

species which appears to rely on specific call repertoires to portray relative fitness and

attract mates Reduction of acoustic habitat by anthropogenic noise may emerge as a

compounding environmental stressor for an already sensitive taxonomic group

copyCopyright by Danielle V Nelson

December 7 2015

All Rights Reserved

THE EFFECTS OF ROAD NOISE ON PACIFIC CHORUS FROG

COMMUNICATION

by

Danielle V Nelson

A THESIS

submitted to

Oregon State University

in partial fulfillment of

the requirements for the

degree of

Master of Science

Presented December 7 2015

Commencement June 2016

Master of Science thesis of Danielle V Nelson presented on December 7 2015

APPROVED

Major Professor representing Forest Ecosystems and Society

Head of the Department of Forest Ecosystems and Society

Dean of the Graduate School

I understand that my thesis will become part of the permanent collection of Oregon State

University libraries My signature below authorizes release of my thesis to any reader

upon request

`

Danielle V Nelson Author

ACKNOWLEDGEMENTS

I would like to express my gratitude first to the amazing community of students

faculty and staff in both Forest Ecosystems and Society and Fisheries and Wildlife for

their continued support and encouragement The Department of Fisheries and Wildlife

the Department of Forest Ecosystems and Society the College of Forestry and the OSU

Graduate School have provided generous financial support through fellowships research

assistantships teaching assistantships and grants I would especially like to thank Lisa

Ganio for her help with the statistical portion of this thesis I would also like to extend my

gratitude to the American Museum of Natural History for financial support

Thank you to George Mueller-Warrant for his initial help in site selection and GIS

work Additional thanks to Molly Monroe at Willamette Valley National Wildlife Refuge

Complex Kyle Martin at E E Wilson Wildlife Refuge Benton County Department of

Parks and Recreation Albany Public Works Tom Malpass Brian Glaser and Jesse

Farver for all their land access help

Gratitude for the initial inspiration for this project falls entirely on Dr Allison

Sacerdote-Velat of the Lincoln Park Zoo in Chicago Without her course in herpetology

her enthusiasm for frogs and her willingness to think outside the box I never would have

considered developing this project further I thank her profusely for her inspiration and

her continuing friendship and look forward to collaboration with her in the future

Many many thanks to Dr Matthew Betts and Dr Sarah J K Frey of Forest

Ecosystems and Society and Dr Peter Wrege of Cornellrsquos Bioacoustics Research Project

for loans of Songmeters for my field seasons

I benefitted immensely from the support of my committee Thank you to Dr

Anita Morzillo of the University of Connecticut for her work in getting me to OSU and

starting me on this path Dr Brenda McComb of OSU Graduate School was invaluable in

her intellectual administrative and personal support I have so much gratitude for her

stepping up every time I needed her to And to Dr Holger Klinck of OSU FW and

Cornell Lab of Ornithologyrsquos BRP a hefeweizen of thanks for all his guidance for

pushing me when I needed it (and sometimes when I didnrsquot) his support and his

formidable acoustic knowledge

My intrepid undergraduate field team made this project possible Thank you to

my two team leaders Codey L Mathis and Ian Lively as well as my students Alexander

Carbaugh-Rutland Elle Bierman Aria Miles and Kurt Tibbals Without them this

project would have been so much more difficult and I am grateful to them for their

willingness to stand in cold ponds in waders late at night hike through snow and carry

equipment I apologize for inflicting my podcasts and weird tastes in music on you

Without the intellectual and emotional support of the OSU Research Collective

for Applied Acoustics (ORCAA) and the Garcia Lab this project would have been a

much more difficult journey I am immensely grateful for their friendship and many

many pep talks Thank you especially to Evan Bredeweg and Jenny Urbina who always

made themselves available for fieldwork to Samara Haver for her willingness to venture

into the terrestrial realm for a night and to Lindsey Thurman and Michelle Fournet for

many many things

A huge thank you to my advisor Dr Tiffany Garcia for taking me on when I

needed a mentor She gave me the opportunity to present to her lab and I never left and

the community she fosters has been the most worthwhile part of graduate school She is a

motivator a mentor a friend and an inspiration and I am excited to continue working

with her

My parents have always been incredibly supportive of whatever pursuit Irsquove set

my mind to and I am extremely grateful to them for everything they have done for me I

love you both very much There are not enough words to express my gratitude and love

to Kevin White who has kept me grounded sane and immensely loved during this

journey and has been a great reminder of the importance of work-life balance

To all my family and friends words do not do justice to your love and support

but I will say it anyway thank you

CONTRIBUTION OF AUTHORS

Tiffany S Garcia contributed to study design in Chapter 2 and assisted in editing all

aspects of the thesis Holger Klinck contributed to study design and acoustic analyses in

Chapter 2 Alexander Carbaugh-Rutland and Codey L Mathis contributed to study

implementation and data analysis in Chapter 2 Anita Morzillo contributed to funding

acquisition and study design in Chapter 2

TABLE OF CONTENTS

Page

CHAPTER 1 - General introduction1

CHAPTER 2 - Pacific chorus frog acoustic habitat the spatio-temporal constraint of road

noise on communication 8

ABSTRACT9

INTRODUCTION 10

METHODS 13

Field methods13

Data processing and analysis 15

Statistical analysis 17

Active communication space-time model17

RESULTS 18

Ambient noise levels18

Call structure 18

Active communication space-time19

DISCUSSION19

TABLES 25

CHAPTER 3 ndash Conclusions 35

LITERATURE CITED 39

APPENDIX - Seasonal and Diel Vocal Behavior of the Northern Red-legged Frog Rana

aurora 44

ABSTRACT45

INTRODUCTION 46

METHODS 47

Data collection 47

Data analysis 48

RESULTS 48

DISCUSSION49

ACKNOWLEDGEMENTS50

LITERATURE CITED 52

LIST OF FIGURES Figure Page

Figure 1 sites used for analysis Year 1 Talking Water Gardens Finley Finger Bond Butte and Jackson Frazier Year 2 all but Talking Water Gardens29

Figure 2 a) 1-second spectrogram of a single Pacific chorus frog call b) 15-second spectrogram of road noise in overlapping bandwidth of frog call 30

Figure 3 ambient road noise levels (dB re 20 micropa) per site against distance from busy road (km) (t6 = -633 p lt 0005)31

Figure 4 confidence intervals of slope estimates for each parameter of interest 32

Figure 5 a) raw data of call rate against noise level color-coded by temperature b) raw data of call rate between 9 and 12 degrees C against noise level with linear model c) predicted relationship of call rate against noise level at each temperature (color-coded) 33

Figure 6 model of communication space-time for each site represented by the circles and their size as a factor of distance from busy road and noise level Radius is measured in meters and call rate is measured in calls per minute34

Figure 7 Total daily hours spent calling 1200-1200 Line indicates the median 7675 hours per 24-hour period Blue line indicates temperature in degrees C54

Figure 8 Time of chorus start as difference from sunset (median = 67 h dotted line) Shaded area indicates hours after sunset unshaded area indicates daylight hours Blue line indicates temperature in degrees C 55

Figure 9 Long-term spectral average (LTSA) plot of Finley Office Pond underwater soundscape recorded on February 5 2014 at 0200 UTC (upper panel) Spectrogram showing individual red-legged frog calls (lower panel) 56

LIST OF TABLES Table Page

Table 1 List of sites years recorded gain settings number of frogs (n) and number of recording nights (nights where directional recording took place) 25

Table 2 summary of parameters by site Mean recording distance is the average of the distance between the microphone and the frog recorded over all recording sessions 26

Table 3 model statistics for call rate frequency duration and source level27

Table 4 Radius and active communication space time (Time-area) related to noise level and call rate 28

DEDICATION

To two brilliant amazing women I lost when I was just starting my graduate school

career Courtney Wilson gone too soon and Phyllis Parizek my indomitable

grandmother I hope I have done you both justice

1

CHAPTER 1 - General introduction

SOUNDSCAPES

Soundscapes are defined as the collection of biological abiotic and

anthropogenic sounds that are an integral part of a landscape that change

spatiotemporally to reflect ecosystem processes (Pijanowski Farina et al 2011) Natural

soundscapes are generally a good indicator of ecosystem health (Sueur et al 2014)

provide information to organisms within them (Pijanowski Villanueva-Rivera et al

2011) and have cultural significance (Dumyahn and Pijanowski 2011a) Soundscape

ecology draws parallels to landscape ecology and biogeography and focuses on the

spatiotemporal patterns of sound at multiple scales the interactions of the three

components of a soundscape and soundscape monitoring and conservation (Pijanowski

Farina et al 2011) Comprehensive assessment of soundscapes should include input from

multiple other fields including spatial ecology psychoacoustics (human cognition and

perception of sound) acoustic ecology (classification and aesthetic value of ambient

sounds) and bioacoustics (Pijanowski Farina et al 2011)

ANIMAL ACOUSTIC COMMUNICATION

Bioacoustics is the study of animal acoustic communication and all that it entails

sound production and perception morphology evolution of sound production and

hearing and heterospecific interactions (Bradbury and Vehrencamp 2011) Soundscapes

can provide information across the entire community of organisms Intraspecific acoustic

communication is used by wildlife for many purposes for example alarm calls (Ridley et

al 2007) social interaction (Awbrey 1978) and attracting mates (Gerhardt and Huber

2002) It is used across a wide array of taxa including invertebrates and many classes of

vertebrates (Bradbury and Vehrencamp 2011) Additionally bioacoustics encompasses

inter-specific eavesdropping on other species communication (Ridley et al 2014) and

predator-prey interactions (Holderied et al 2011)

2

ANTHROPOGENIC NOISE IMPACTS

When a soundscape is altered in a way where anthropogenic noise overpowers

abiotic and biotic sounds information is lost Anthropogenic noise is generally

characterized as being low-frequency but broadband its energy is spread over a wide

range that overlaps with many of the frequencies used by species to communicate

acoustically (Barber et al 2010) The main sources of anthropogenic noise come from

transportation motor vehicles on roads airplanes and in the marine realm ships

(McGregor et al 2013) It can be either acute (like sirens from emergency vehicles) or

chronic (air traffic vehicle traffic) Due to widespread human encroachment through

roads and air traffic flyover chronic anthropogenic noise has been shown to be audible

even in places where humans are not frequently found and to be fairly consistent

temporally (Barber et al 2011)

At an individual level chronic anthropogenic noise can cause physiological

reactions that can have a direct impact on fitness and reproductive success These can

include hypertension stress and hearing loss (Barber et al 2010) Humans are not

exempt from this studies of children exposed to high levels of chronic anthropogenic

noise even levels below those found to cause hearing loss show elevated levels of stress

hormones and depressed quality-of-life indicators (Evans et al 1998) Responses in

wildlife are similar stress hormone levels are generally elevated in most taxa in chronic

high-noise environments (Barber et al 2010) In many species elevated stress hormone

levels can affect the fitness of individuals (Creel et al 2013) therefore noise can lead to

fitness impacts on individuals even before addressing the implications of reduced

conspecific communication Additionally there are many taxa that use vocalizations and

acoustic cues to forage or to escape from predation Bats have been shown to have

reduced foraging success near noisy roads due to an inability to hear the rustling sounds

of their prey which has direct impacts on their fitness (Siemers and A Schaub 2011)

At the population and community level the more insidious impact of

anthropogenic noise in an ecosystem is that of masking or the loss of communicated

information due to the interference of background noise Masking can impact the ability

of conspecifics to communicate information with each other which can have implications

for mating success group cohesion and other important social processes While many of

3

these implications have not been tested directly studies have shown in many taxa such as

marine mammals (Hatch et al 2012) birds (Slabbekoorn and Peet 2003) bats (Hage et

al 2013) and anurans (Wollerman and Wiley 2002) that communication is hindered by

high levels of anthropogenic noise With a reduction in the ability to perform such vital

tasks as attracting a mate through acoustic vocalization (Gerhardt and Huber 2002) there

may be population-level implications of increased anthropogenic noise species especially

in already-threatened species Animals can modify their vocalizations to counteract the

effects of masking with mixed effects Often these modifications can be energetically

costly (Barber et al 2010 Zollinger and Brumm 2011) It is unclear what trade-offs are

induced by this increased energetic cost but these may also provide additional pressure

on already stressed populations

Anthropogenic noise can also have community-level impacts that can shift the

species distributions and interactions within an ecosystem This can be in part due to the

population-level effects mentioned above however interactions such as

eavesdropping or the cueing in on information by an individual other than the intended

receiver (Ridley et al 2014) Goodale et al (2010) suggest that the sharing of

heterospecific information is one of the primary drivers in the formation and maintenance

of temporary or stable mixed-species groups and it may also help with habitat selection

in species These groups provide benefits to their members mixed-species groups may

provide different ways of perceiving information than single-species groups while

removing some of the competition pressure found in single-species groups For example

Ridley et al (2014) found that a species of bird (scimitarbills) would shift from foraging

in trees to ground foraging in the presence of another species of bird (pied babblers) that

produced alarm calls thereby changing the foraging pressure on ground vegetation and

invertebrates depending on the alarm call species There is also the theory of the

heterospecific attraction hypothesis which describes a situation where individuals choose

habitat patches based on the presence of resident heterospecific individuals (Moumlnkkoumlnen

et al 1999) This has been primarily studied in birds and has been proposed as a

mechanism allowing migrant birds to select high-quality habitat based on the presence of

residents who would necessarily have more time to assess habitat quality (Moumlnkkoumlnen et

al 1997) Song may be a far-reaching cue of resident presence which will affect the

4

development of a migratory bird community that depends on the presence of residents

Anthropogenic noise has the potential to mask any of this information exchange which

may alter community interactions

FROG COMMUNICATION

The impacts of anthropogenic noise are still widely unstudied in many taxa and

since different species have very different responses to noise it is important to quantify

these impacts in order to better understand how to conserve soundscapes and vocalizing

species Among these understudied taxa are the anurans or frogs and toads Of the class

Amphibia only anurans are known to vocalize (Gerhardt and Huber 2002) Vocalization

in this order is used primarily for breeding Males will produce calls that are used to

attract females to breeding ponds (Narins 2007) Additionally other calls are used to

mediate male-male interactions (Brenowitz and Rose 1994) release calls used by both

males and females in breeding situations (Sullivan and Wagner 1988) and territorial calls

(D Schaub and Larsen 1978) Vocalizations are often highly stereotyped and are innate

rather than learned (Narins 2007)

While frog vocalizations have been studied for many years (Gerhardt and Huber

2002) the impacts of noise on their communication are still relatively unclear While

some studies have been done (Lengagne 2008 Kaiser and Hammers 2009 Cunnington

and Fahrig 2012) the population and community level effects of anthropogenic noise on

anurans are unclear Given that many anurans vocalize in single- or multi-species

choruses there is the potential for dramatic shifts in energy expenditure population

structure and community dynamics if anuran vocalization is impacted by anthropogenic

noise

Amphibians (including anurans) are ectothermic their energy expenditures are at

least partially governed by the external temperature of their surroundings (Whitford

1973) In general lower external temperatures are associated with lower activity levels in

this class (Bennett 1978) This extends to vocalization as well which can be related to

temperature constraints (Wells et al 1996) While this is mediated by social context in

some species (Wong et al 2004) it is unclear how social context and temperature interact

across the order to influence aspects of call structure such as call rate Additionally given

5

the diverse evolutionary and developmental histories of amphibians the wide range of

habitat types in which they are found and the considerable vocal diversity displayed by

anurans generalization of conclusions from one species across others is unlikely to be

reasonable (Narins 2007) Instead a species-by-species approach is likely the best way to

determine vocal behavioral norms

Vocal production

The mechanism for production of calls in anurans involves passive vibration of

vocal membranes in the larynx through movement of air from the lungs into the mouth

and vocal sac which acts as a resonant structure used to amplify the call focus the

energy into the second harmonic and cause the signal to be omnidirectional (Gridi-Papp

2014) Dominant frequency is tied to body size in many species of frog and there is some

evidence of frequency plasticity in some species of frog in response to modified

conspecific vocalization (Lopez et al 1988) however it is unclear how universal this is

given the diversity of vocal anuran species and the differing rates of evolution of anuran

vocalization among species (Cocroft and Ryan 1995) As the vocal mechanism is passive

this frequency adjustment is likely achieved through manipulation of the pressures before

and after the larynx and is likely to be energetically costly to change (Gridi-Papp 2014)

Anurans will more readily change the temporal aspects (call rate call duration) of

their calls (Bee and Schwartz 2013) Often call rate and call duration are inversely related

(Bee and Schwartz 2013) so longer calls will be produced less often than shorter calls for

a given species Call rate will increase with increasing temperature as energy levels will

increase at higher temperatures (Wells et al 1996) Frogs will also cease calling after a

disturbance andor alter their timing of calling to take advantage of natural lulls in chorus

noise (Sun and Narins 2005 Velez and Bee 2011) Additionally call rate can be

increased with proximity of other frogs as calling individuals either attempt to attract the

frog (if it is female) or warn it away (if it is another male) (Allan 1973)

Hearing and perception

Hearing in many species of anuran (but not all) occurs when a sound vibrates the

external tympanic membrane located on the side of the head (Mason 2007) From there

vibrations of the tympanic membrane vibrate in turn the stapes which transmits sound

through the oval window to the inner ear The inner ear in amphibians is comprised of

6

two specialized mechanisms the amphibian papilla and the basilar papilla These two

structures are tuned to different frequency ranges the amphibian papilla specializes in

low-frequency sounds and the basilar papilla is more sensitive to higher frequency

ranges (Gerhardt and Bee 2007) Additionally the amphibian papilla frequency range can

be influenced by the external ambient temperature (Lewis and Narins 1999) Hearing in

anurans is thought to be related to the frequency range in which conspecific vocalization

occurs (Gerhardt and Huber 2002) although there are species which can perceive

frequencies outside of that range (Simmons and Moss 1985) However this cannot be

generalized across all species

Localization of conspecific calls in higher vertebrates is dependent on the

difference in arrival time between the two ears which in turn is dependent on the

frequency of the sound being small enough to not exceed the dimensions of the

perceiverrsquos head (Gerhardt and Bee 2007) In anurans this process is considerably more

difficult given the generally small binaural width The exact biophysical process by

which anurans are able to localize conspecific callers is unknown however it is

hypothesized that localization involves some method of pressure differentiation andor

extratympanic input ie the sound may come to the inner ear through multiple pathways

that bypass the tympanic membrane (Gerhardt and Huber 2002) More research is needed

to determine the exact biophysical method of localization in vocalizing anurans

PACIFIC CHORUS FROG LIFE HISTORY

The Pacific chorus frog (Pseudacris regilla) is a small (3-4 cm) highly vocal

anuran native to the western United States (Jones et al 2005) They range from British

Columbia to Baja California and as far east as Montana (Jones et al 2005) The species

can be found in most still-water aquatic habitats below 10000 feet in elevation (Leonard

1993) They are prolonged breeders and will vocalize in dense choruses from very early

spring or late winter until late spring in a diversity of still-water habitat types While

adults are terrestrial breeding and development of this species is aquatic

Beginning in late winter male Pacific chorus frogs will move from their non-

breeding habitat (usually wooded areas) to still-water breeding habitats Males will then

vocalize not only to establish temporary territories but also to attract females to the

7

breeding pond (Brattstrom and Warren 1955) It is thought that like many species of

vocal anurans females will use cues within the call to localize and choose a mate (Snyder

and Jameson 1965 Allan 1973)

This species has a characteristic ribbit sound that constitutes an advertisement

call used by males for mate attraction (Snyder and Jameson 1965 Allan 1973) For the

advertisement call most of the energy is centered around the dominant frequency at

approximately 25 kHz (Allan 1973) The call is comprised of two syllables and its

frequency modulates slightly upward in the second syllable (Snyder and Jameson 1965)

Two other calls are produced by males in different contexts one a monosyllabic call is

used when a frog of unknown sex approaches the calling male the second an encounter

trill call is used to defend calling territory from an encroaching male (Allan 1973)

Once a female has chosen a mate the pair will enter amplexus during which the

male will clasp the female under her arms Eggs will be laid in a loose circular clump

attached to vegetation and fertilized externally during amplexus (Jones et al 2005) Eggs

develop into tadpoles within 1-5 weeks (Leonard 1993) Tadpoles in western Oregon

usually metamorphose within 2 months of hatching after which they disperse from their

natal ponds (Nussbaum et al 1983) Movements of Pacific chorus frogs outside of the

breeding season are not well known (Jones et al 2005)

RESEARCH QUESTIONS

We investigated the impacts of road noise on calling Pacific chorus frogs

(Pseudacris regilla) throughout the Willamette Valley across a gradient of noise

exposure Our goal was to determine if there were any changes to acoustic parameters

(call source level frequency rate and duration) in relation to differing levels of road

noise There has been no work done on the behavioral audiogram or female orientation of

this species We used passive acoustic monitoring to document soundscapes at eight sites

and directional acoustic recording to record individual calling frogs at each of those sites

across a breeding season Acoustic parameters were then extracted and compared across a

range of noise exposures and temperatures to determine how Pacific chorus frogs

changed their communication

8


noise on communication

Danielle V Nelson Alexander Carbaugh-Rutland Codey L Mathis Anita Morzillo

Holger Klinck and Tiffany S Garcia

9

ABSTRACT


























10

INTRODUCTION

Natural soundscapes or the combination of biotic and abiotic sounds reflect

important ecological processes (Pijanowski Villanueva-Rivera et al 2011) One such

process is animal acoustic communication which is used by multiple taxa to convey

information on mate fitness food availability and often warning signals (Barber et al

2010) Among these vocal taxa are anurans or frogs and toads many species of which

use acoustic communication to attract mates and defend territories (Gerhardt and Huber

2002) Anuran acoustic signals are produced primarily by males during breeding season

and used to portray a fitness advantage over competing males (eg larger body size) to

conspecific females (Gerhardt and Huber 2002) These signals are innate rather than

learned and anurans were thought for a long time to lack the vocal plasticity to change

their vocalizations based on surrounding soundscapes (Narins 2007)

Increasing anthropogenic noise levels and urban encroachment are altering natural

soundscapes in nearly every ecosystem worldwide often to the detriment of organisms

that share and utilize this acoustic space (Clark et al 2009 Barber et al 2011 Dumyahn

and Pijanowski 2011b Tucker et al 2014) The primary sources of anthropogenic noise

are transportation-related (eg motor vehicles air traffic and shipping noise) which

have been found to interfere with acoustic communication through masking or the

reduction of the active space over which the signal (ie vocalization) can be perceived

Traditionally this active space has been described as the spatial projection of

vocalizations but it can also be characterized along a temporal axis Thus active space is

actually an active three-dimensional communication space-time Signal masking and the

reduction of active communication space-time can constrain animal communication

which can adversely impact reproductive success through loss of important

communicated information such as mate fitness or foraging location (McGregor et al

2013) This has been found in many taxa from whales (Clark et al 2009) to bats (Hage et

al 2013) to birds (Slabbekoorn 2003)

Acoustic species including anurans can modify their vocalizations to compensate

for masking and optimize their communication space-time There are several call

parameters that can be shifted by vocal species Increasing source level (changing signal

11

amplitude or getting louder) in the face of noise masking termed the Lombard effect

(Zollinger and Brumm 2011) is a mechanism for maintaining communication dynamics

in an increasingly noisy environment The Lombard effect has been detected in response

to masking in songbirds (Brumm and Todt 2002) killer whales (Holt et al 2009) bats

(Hage et al 2013) and several other species (Zollinger and Brumm 2011) however

there is no conclusive evidence of the Lombard effect in vocalizing anurans (Bee and

Schwartz 2013) While it is possible for at least one species of frog to change the

amplitude of its vocalization (Lopez et al 1988) of the few studies done examining the

response in source level to noise none has shown an increase in amplitude in vocalizing

male frogs in response to noise

Another mechanism to compensate for masking by noise is to change the

temporal aspect of calls (Bee and Schwartz 2013) such as altering the timing of

vocalizations by changing the duration of the call or by changing how often the call is

produced This response is common in many species of anurans (Lengagne 2008 Kaiser

and Hammers 2009 Cunnington and Fahrig 2010) Lastly acoustic species can change

the call frequency (often described as pitch) so it doesnrsquot overlap that of the noise

(McGregor et al 2013) This method has been seen in both birds (Slabbekoorn and Peet

2003) and anurans (Kaiser and Hammers 2009) It is unclear whether the active space (or

space-time) of a communicating animal is increased andor maintained by these changes

to vocalization behavior

While anuran acoustic communication has been studied for many years

significant data gaps exist regarding species response to anthropogenic noise and the

population and community-level implications of this response (or lack of response)

particularly as they relate to constraints in communication space-time The predominant

response to noise in vocalizing anurans is changes in the temporal patterning of calls (rate

and duration (Bee and Schwartz 2013) Interestingly changes in call duration and call

rate are often negatively correlated (Bee and Schwartz 2013) when a vocalizing frog

reduces call rate it will often increase call duration For example several frog species

across different habitats have been found to reduce their call rate in the presence of traffic

noise A reduction in call rate may indicate the reduction of the total time spent calling if

there is no corresponding increase in duration However it remains unclear the extent to

12

which these modifications of anuran vocalizations increase the active space-time for an

individual or how these modifications impact energy expenditure or induce trade-offs

with other important behaviors or traits (Bee and Schwartz 2013 McGregor et al 2013)


anuran native to the western United States (Jones et al 2005) They are prolonged

breeders and will vocalize in dense choruses from very early spring or late winter until

late spring in a diversity of still water habitat types They have a characteristic ldquoribbitrdquo

sound that constitutes an advertisement call used by males for mate attraction (Snyder

and Jameson 1965 Allan 1973) For the advertisement call most of the energy is

centered around the dominant frequency at approximately 25 kHz (Allan 1973) The call

is comprised of two syllables and its frequency modulates slightly upward in the second

syllable (Snyder and Jameson 1965) The Pacific chorus frog is an ideal study species to

examine road noise impacts as it breeds readily in both noisy disturbed habitats as well

as quiet undisturbed habitats (Jones et al 2005) Further the lower frequency bands of

its calls overlap with the upper frequencies of road noise which may mask

communication

We studied the call structure of populations of Pacific chorus frogs at eight

breeding sites in the Willamette Valley Oregon across a gradient of traffic noise

exposures to quantify changes in dominant frequency call rate duration and source level

in response to differing levels of noise We predicted that frogs would adjust their call

structure in a way that would maintain their active communication space-time in noisy

areas We expected that dominant frequency would increase with increasing levels of

road noise and that call duration and call rate would be inversely correlated and

dependent on road noise level We did not expect to see any difference in call source

level because of previous literature indicating that the Lombard effect is not seen in

anurans (Bee and Schwartz 2013) We also examined the relationship between seasonal

temperature shifts and call parameters to determine the potential compounding effects of

temperature and noise on call structure Together we provide the first three-dimensional

characterization of anuran vocalization across a wide range of noise exposures and

evidence for noise impacts on their communication space-time

13

METHODS

Field methods

Acoustic monitoring sites were determined based on the existence of breeding

populations of Pacific chorus frogs and landowner cooperation for access to breeding

ponds Based on these criteria sites were chosen across a gradient of noise exposures

determined by varying distance from roads with greater than 30000 Annual Average

Daily Traffic (AADT from Oregon Dept of Transportation) Monitoring and sampling

was conducted over two years (2014-2015) during two consecutive Pacific chorus frog

breeding seasons (February-May) Meteorological data for both years was taken from the

weather station in Finley National Wildlife Refuge Corvallis OR (Figure 1)

Passive acoustic recorders

We utilized passive acoustic recordings to document the soundscape of each

breeding site We characterized the anthropogenic and anuran components of each sitersquos

soundscape over the course of the breeding season by quantifying ambient road noise

levels and timing as well as general chorus structure Passive recorders

(WildlifeAcoustics Songmeter models SM1 SM2 and SM2+ with two microphones

recording in stereo microphone sensitivity -35 plusmn 4 dB for SM1 -36 plusmn 4 for SM2 and

SM2+) were installed at all sites (Table 1 Figure 1) and left in place for the duration of

the breeding season Battery changes and data storage downloads were performed

biweekly Recorder sampling rate was set at 441 kHz with 16-bit resolution producing

recordings with a frequency range of 0-22050 Hz Gain settings varied by recorder

(Table 1)

Songmeter recording schedules in 2014 were based on the timing of sunset due to

the crepuscular nature of calling in this species (Allan 1973) Recordings began one hour

before sunset and continued for 4 hours total This schedule operated daily and tracked

sunset based on input GPS coordinates In 2015 the recording schedule was extended to

8 hours from 4pm to midnight daily (Feb 1 - Apr 5) and then from 4pm to 2am daily

(Apr 6 - end of breeding chorus activity) this was done to attempt to capture the end of

the chorus each night but was unsuccessful The change in recording time has no effect

14

on any of the results presented here Recorder time was not changed to compensate for

daylight savings time therefore all recordings were made in Pacific Standard Time

Directional acoustic recording

In both years frogs were chosen for recording haphazardly Individual calling

frogs were localized by the observer before recording began All sources of visible light

used by the observer were extinguished prior to recording to minimize disturbance to the

animal and the animal was allowed to begin calling again after approaching it before

recording was begun Gain settings on the Zoom H4n recorder were adjusted to maximize

individual detectability prior to the start of recording Recording surveys were done in

such a way to minimize the possibility of recording the same individual more than once

per night by consistently walking in one direction and not returning to areas where a frog

had already been recorded Additionally recording surveys were started at different

haphazardly chosen points each survey night to reduce the possibility of recording the

same individual more than once per recording season

Directional recording was completed at four sites in 2014 and at seven sites in

2015 (three of the four 2014 sites and four additional sites) Eight different sites total

were used These recordings quantified and allowed for categorization of multiple

individual frog call parameters within each site Individual frogs were recorded in situ for

3-5 minutes and measurement of distance from the microphone to an individual frog was

done after recording was complete The recording equipment was comprised of a

Sennheiser MKH20 microphone (sensitivity 0025 Vpa) in a Telinga parabolic

directional housing attached to a Zoom H4n recorder with SD storage Single channel

recordings at a sampling rate of 441 kHz with 16-bit resolution were produced Gain

settings were manually adjusted on the H4n recorder to maximize individual frog

detectability and were noted for later reference

During 2014 17 total successful individual frog recordings were made Distance

from the microphone to the frog was taken with a tape measure after recording was

complete Four to eight were recorded per site (Table 1) During 2015 recording was

conducted at seven sites Recordings were taken throughout the breeding season in order

to account for any possible seasonal effects At least 10 frogs were recorded per site with

15

80 total frogs recorded across both years After recording was complete the distance

from the microphone to the frog was measured and documented with a tape measure At

least 5 minutes were allowed to pass between individual recordings to allow surrounding

frogs to recover from any disturbance by the observers

Data processing and analysis


Data were processed using program SoX (Bagwell 2013) using an R script which

enables batch processing of large audio files All data were initially processed into single-

channel audio files Audio files were put through a 1-45 kHz bandpass filter to highlight

any noise within the bandwidth of the Pacific chorus frog call SoX was used to extract

RMS amplitude measures on this limited bandwidth To determine ambient road noise

level without confounded frog chorusing for a given night of directional recording the

RMS amplitude of the files between 1600 and 1700 was averaged and converted in

program R to decibel (dB re 20 micropascal) measurements using microphone

specifications and gain settings This time period was chosen because it is very unlikely

that there would be a substantial frog chorus in those hours (pre-sunset) during the

breeding season as such it constitutes an accurate assessment of the ambient road noise

levels at each site given the lack of a substantial rush hour along this section of Interstate

5 because of lack of proximity to large cities (Schaub and Larsen 1978)

Directional acoustic recordings

Spectrograms of each directional recording were generated using RavenPro 15

with 256 point Fast Fourier Transform (FFT) Hann window and 50 overlap and the

MATLAB-based program Osprey using the same parameters except a Hamming window

Recordings were manually reviewed and each call from an individual frog was counted

using RavenPro 15 (Cornell Lab of Ornithology) Calls that did not overlap with other

individual frog calls and which had visually and aurally distinctive start and end points

were selected for further analysis of frequency time and source level parameters

Selections were manually drawn to encompass the start and end points of each two-

16

syllable call To encompass the majority of the energy of each call while excluding most

of the low-frequency road noise measurements were restricted to the bandwidth of 1-45

kHz Within this bandwidth filtered RMS source levels were extracted using SoX and

converted in R using the microphone specifications and recorder gain settings to decibel

level (dB re 20 micropascals) Peak overall frequency measures were taken using a 8192-

point FFT based on the 3dB filter bandwidth of 775 Hz

These selected calls were then analyzed for parameters (dominant frequency and

duration) from the Noise-Resistant Feature Set (NRFS (Mellinger and Bradbury 2007)

within the MATLAB-based program Osprey While the NRFS was designed to be used

for measurement and classification of marine animal sounds in noisy environments it has

robustly extracted parameters from terrestrial recordings as well The NRFS allows the

loudest parts of the spectrogram to have the strongest influence on the calculated feature

values (Mellinger and Bradbury 2007) These parameters correspond to more traditional

acoustic measurements but are considered more robust to attenuation and noise

conditions This is particularly important for this study given the range of noise

conditions found across the sites depending on proximity to high-volume roads Measures

used from the NRFS were duration (M5) and frequency of peak overall intensity (M20)

Once acoustic analysis was complete for directional recordings all data were imported

into R (R Core Team 2015) for statistical analyses

Call parameters extracted from the directional recordings for the purposes of this

study were filtered RMS source level (later converted to dB re 20 micropascal) call

duration (s) peak overall frequency (Hz) and call rate (defined as the number of calls per

minute of recording) Analysis was performed at the level of an individual calling male

frog call duration peak overall frequency and filtered RMS source level were averaged

across all calls for an individual Ambient noise measures were extracted per day of

directional recording in the bandwidth of 1-45 kHz during the hours of 1600-1700 to

prevent confounding of noise measurements by the frog chorus In addition temperature

measurements that were taken at hourly intervals over each day were also averaged

between the hours of 1900 and 2200 for a given night of directional recording Noise

levels were modeled by site against the distance from a road with AADT (annual average

daily traffic) greater than or equal to 30000 cars to maximize noise exposure Of the 105

17

frogs recorded (year 1 n = 25 year 2 n = 80) 90 frog recordings (year 1 n = 20 year 2

n = 70) were deemed useable for further analysis due to lack of overlap with other calling

frogs and high signal-to-noise ratio Passive recorder failure occurred on several days

throughout each season due to battery failure andor poor weather conditions Therefore

only days with complete data were used in noise analyses

Statistical analysis

To examine the effects of road noise and temperature covariates on Pacific chorus

frog call structure we constructed a linear mixed effects model The response variables

of interest were source level frequency call rate and call duration for individual frogs

All response variable data were normally distributed and no transformations were

necessary The variables noise and temperature were included as fixed main effects

(covariates) and site was included as a random effect to account for any random error

created by breeding site-level differences Models of each response variable against

seasonality were examined no effect of date or seasonality was found so the term was

dropped from all subsequent models After accounting for the effects of temperature and

ambient road noise no significant interaction was found between ambient road noise and

temperature in any model Therefore all models were run without an interaction term

Visual inspection of residual plots did not reveal any obvious deviations from

homoscedasticity or normality for the parameters of call rate mean frequency and mean

source level Heteroscedasticity was observed for the model for duration so assumptions

of equal variance were relaxed All statistical analyses were conducted using R (R Core

Team 2015) and package nlme (Pinheiro and Bates 2015)

Active communication space-time model

A model was created (Eq 1) of the received level (RL) for individual frogs based

on a) the source levels (s) and call frequencies (f) of frogs in this study and b) ambient

road noise levels (n) across our breeding sites (Embleton 1996) At the distances and

frequencies we observed for this species atmospheric absorption had a negligible effect

on received levels and was therefore excluded from the model

18

= $ minus 20 log+ - Equation 1

Using this model of attenuation the radius (r) at which the received level was

attenuated to the point at which it could no longer be heard over the background noise n

was calculated This was then used to calculate the circular area of the communication

space Additionally a temporal component was incorporated by using the predicted call

rates from given temperatures and noise levels based on the statistical model Using these

and a constant duration (d = 016 s) the space-time was calculated from a time-area

calculation (Miller 1999) of an individual calling frog for a given minute at a given

temperature of 10 degrees C (Eq 2)

$012341 = 055-21(78-9) Equation 2

RESULTS

Ambient noise levels

Ambient noise levels differed among sites decreasing with increasing distance

from a road with 30000 or more average cars per day which encompassed Interstate 5

and some areas of Highway 99 near Salem When modeled against A = 1distance^2 as

predicted by the inverse square law for sound propagation outdoors (Embleton 1996)

noise levels differed significantly with increasing distance (t6 = -633 p lt 0005) Sites

close to busy roads (lt 1 km) averaged 5227 dB (SE plusmn04714) during the hours of 1600-

1700 daily while sites farther from busy roads (gt 1 km) averaged 3748 dB (SE

plusmn06633) during those hours (Figure 3) Ambient noise at sites far from roads was due to

wind and rain air traffic flyover bird vocalization and vehicular maintenance at the

sites We found no seasonal or hourly difference in ambient road noise levels at any of

the sites

Call structure

Temperature was found to have a significant effect on call duration (t80 = -5417

p lt 0000) For every 1-degree Celsius increase in temperature call duration was

estimated to decrease by 0008 seconds (SE plusmn1478 x 10-3) Temperature was also found

19

to have a significant effect on call rate (t80 = 3066 p = 0003) For every 1 degree

Celsius increase in temperature call rate is estimated to increase by 178 calls per minute

(SE plusmn0579 Figure 5) However this response is mediated by ambient road noise The

call rates of Pacific chorus frogs decreased significantly with increasing levels of ambient

noise but the magnitude of this response was dependent upon temperature (t80 = -2190 p

= 003 Fig 3) Based on the model it is estimated that a frog will decrease its call rate by

045 calls per minute (SE plusmn0206) per every 1 dB of increasing noise at a given

temperature level keeping temperature constant as in each line in Figure 5 call rate is

lower at higher noise levels and lower temperatures While the difference is small and

falls within the standard deviation of call rate for each site (Table 2) it still constitutes a

significant reduction in the time spent calling Pacific chorus frogs were not found to

change source level (t80 = -0626 p = 05334) or call duration (t80 = 1232 p = 0221) in

response to differing levels of noise exposure The response of peak overall frequency to

noise exposure was weakly significant (t80 = -1916 p = 00589) however the estimated

effect (306 Hz1 dB increase) falls below what would be a significant change in

frequency response We found no seasonal difference in call structure at any of the sites

Active communication space-time

The three-dimensional active communication space-time is reduced for an

individual Pacific chorus frog at sites with relatively high noise levels We identified a

temporal component to male vocalizations at breeding sites nearer to busy roads with

higher ambient road noise levels which was characterized by a reduction in their calling

rates and less time spent calling (Figure 5) Based on modeled data a reduction in the

spatial radius of vocalizations and the total time spent calling were found Therefore there

was an overall reduction in the time-area of communication by several orders of

magnitude at the loudest noise levels observed compared to the quietest (Table 4 Figure

3)

DISCUSSION

20

Our study quantified the effects of ambient road noise on the call structure of

Pacific chorus frogs Noise levels decreased significantly with increasing distance from a

major road with traffic levels above 30000 AADT After accounting for temperature we

found a significant reduction in male calling rate with increasing road noise levels Call

rate was reduced linearly with increasing noise levels by 045 calls per decibel but

temperature determined the magnitude of reduction in calling rate (Figure 5) While

temperature had a significant effect on both call rate and call duration we found no effect

of road noise levels on call duration or source levels The response of frequency was

weakly statistically significant but did not qualify as biologically significant as the

largest shifts between quiet sites and loud sites would still fall within the range of the

standard deviation for a given site

Communication is reduced both spatially and temporally for male Pacific chorus

frogs Using both the reduction in total time spent calling and our model of the reduction

of communication space we created an interactive framework (seen at

httpsdayvayenshinyappsiocirclevis) For any given minute this framework indicates

that the communication space-time is drastically reduced for an individual Pacific chorus

frog at sites with relatively high noise levels (Figure 6) While temperature has a larger

overall impact than noise does according to our model the temperatures observed at the

sites examined did not differ enough among themselves to make a large difference

Therefore at a constant temperature as one would find across the gradient of noise

exposure at our sites noise reduced call rate Even as temperatures warm seasonally or

through global climate change for a given temperature noisier ponds would have a

reduced call rate compared to quieter ponds Thus we have demonstrated that masking of

advertisement calls in this species by road noise significantly impacts active

communication space-time While this model represents an idealized situation because it

fails to account for vegetation position of vocalizing frog temperature and substrate

(Forrest 1994) it can still inform our comparison of high-noise vs low-noise

environments and how management intervention might reduce the impact of noise and

optimize communication space-time for this species

Given the general behavioral plasticity in call rate of anurans (Gerhardt and Huber

2002) it is likely that the reduction in call rate is a plastic response to site-specific road

21

noise levels However further study is needed to determine if this response is plastic or

adaptive as this response could be representative of localized adaptation to chronic noise

levels Call rate reduction has been found in other anuran species experiencing high noise

levels (Lengagne 2008 Cunnington and Fahrig 2010 Herrera-Montes and Aide 2011)

however this increase in call rate was paired with a corresponding increase in the

duration of each call (Bee and Schwartz 2013) While we found no correlative

relationship between these parameters both were significantly related to temperature A

decrease in call rate results in a direct reduction in the total amount of time spent calling

albeit not the call duration per se of an individual vocalization This has significant

implications for reproductive success in noisy areas as females may have less total time

to assess males Females use auditory cues embedded in male calls to assess relative

fitness (Gerhardt and Huber 2002) These include dominant frequency to assess potential

mate size as well as call rate to assess overall energy use and fitness a fitter healthier

male will call more often per minute (Wells et al 1996) Frogs at noisier ponds may

therefore be indicating a comparatively lower level of fitness whether or not their fitness

is actually lower Additionally females use the calls of males especially in choruses to

orient toward breeding ponds at the onset of breeding season (Narins 2007) With fewer

opportunities to judge mate fitness the perception of lower fitness due to reduced call

rate and a decreased distance over which calls can be perceived females may be

incorrectly assessing and thus responding to advertising males or even not responding to

males at all Further the masking of choruses by road noise could inhibit females from

efficiently localizing to breeding ponds in the first place

Males that communicate within the bandwidth of ambient road noise will likely

experience selective pressure to adjust their call parameters to differentiate the signal

from background noise (ie the acoustic adaptation hypothesis (Wiley 2013)

Hypothetically this may be accomplished by shifting the frequency of the vocalization

such that it no longer overlaps with the background noise by increasing the amplitude of

the vocalization to increase the signal-to-noise ratio and propagate further or by

increasing the duration of the vocalization to provide a longer opportunity for perception

(Wiley 2013) Other than call rate we found none of these acoustic adaptations in our

22

study call rate reduction does not aid in differentiation of the sound from background

levels and in fact creates fewer opportunities for doing so

This finding implies that Pacific chorus frogs may lack the capacity to modify

their vocalizations in such a way that allows them to be heard over increasing noise

levels Without behaviorally or phenotypically plastic vocal adaptation to higher noise

levels it is likely that frogs living in high-noise areas such as found next to a highway

are at a disadvantage when trying to communicate We have also identified a significant

reduction in the communication space-time for Pacific chorus frog populations near noisy

roads It is likely that species such as the Pacific chorus frog that lack vocal plasticity that

will suffer most from noise pollution Without mechanisms to adjust their call structure to

accommodate high noise levels species that cannot expand their active space-time will

be more impacted by the masking effects of noise than other species

The effects masking may have on communication fitness stress levels or

reproductive success are unclear for this species more research is needed to determine

what impacts masking can have when vocal compensation is limited Female responses to

male vocalizations at different noise levels in this species are unknown and future work

should focus on determining how signal discrimination by females is altered by noisy

environments in this species in a congeneric Pseudacris crucifer low to moderate noise

levels induced a desensitization of the auditory system which in turn led to higher

stimulus levels for auditory nerve saturation (Schwartz and Gerhardt 1989) It is also

unclear if the reduction in communication space-time for an individual male may lead to

suboptimal female mate choice Future work should focus on evaluating female responses

to male vocalizations at different noise levels Noise has already been found to increase

stress hormone levels and prevent accurate orientation in female wood frogs (Tennessen

and Parks 2014) this may interact with the masking effects of noise and possibly impact

reproductive success though this interaction has yet to be explored Wollerman et al

(2002) found that female Hyla ebraccata became less choosy between calls of differing

frequencies when exposed to moderate levels of noise such as would be found at the sites

in this study While we did not find any evidence of shifting dominant frequency in our

study this does not mean that the range of frequencies produced gives males the same

amount of mating success especially given how dependent dominant frequency is on

23

body size Furthermore there are still substantial knowledge gaps with regards to the

impacts of chronic noise exposure on males In choruses inter-male spacing and

potentially antagonistic interaction can be very important to the outcome of breeding

events Lengagne (2008) noted that social context had a strong effect on how Hyla

arborea shifted its calling behavior in noisy environments He predicted that the active

space of the chorus would be reduced if there were not enough males present to socially

buffer the impacts of noise Thus as a collective group smaller choruses may lead to

inefficient orientation to breeding ponds by both males and females

Additionally call rate has been found to be density-dependent in other species of

chorusing frogs (Wong et al) call rate is increased in a social situation as opposed to in a

solitary situation (Lengagne 2008 Wong et al) Our results showed a decrease in call

rate with increasing noise levels While we were careful to record at sites that had a

chorus of individuals the size of the chorus was not quantified Therefore although we

have postulated that this may be a plastic behavior in response to high levels of noise it

may be that the decreased call rate is indicative of less dense populations at noisier areas

Therefore the decreased call rate found at noisier sites may actually be indicating less

dense choruses and populations Measuring the call rate of populations may therefore be

a way of indicating population density and deserves further study If population

structures are different at sites with higher noise levels either through less dense choruses

or greater nearest-neighbor distances (Sullivan and Wagner 1988) then high-noise sites

may indicate less fit populations even without a direct impact of noise itself Regardless

where chorus situations had previously mediated the impacts of noise on call rate in other

species (Lengagne 2008) here we found that even within a chorus call rate was reduced

for an individual calling frog at sites with higher noise levels

Lastly we do not know how noise may interact synergistically with other

stressors such as invasive species disease or overall habitat degradation to impact vocal

amphibians While it is likely that noise is not the most severe stressor to which

amphibians are regularly exposed (McGregor et al 2013) it may induce a similar stress

response or exacerbate already degraded habitat As discussed above noise induces

elevated corticosteroid levels in at least one species of frog and across other taxa noise

has been found to cause elevated stress hormone responses that have physiological

24

impacts including decreased growth increased development time and

immunosuppression (Gabor Bosch et al 2013) Recently embryonic mortality and nest

success was found to be deleteriously impacted by increased levels of road noise in

captive zebra finches due to increased stress hormone production (Potvin and

MacDougall-Shackleton 2015) Noise on its own can cause decreased body condition in

migratory birds without the compounding effects of habitat fragmentation caused by the

road itself (Ware et al 2015) More work is needed to determine how noise interacts with

other stressors and how this impacts vocalizing anurans

Infrastructure improvements can aid in noise level reduction The installation of

sound barriers alongside particularly busy stretches of highway can reduce a considerable

amount of noise exposure these can be constructed of concrete or other building

materials (Sanchez-Perez et al 2002) or be as simple as a row of dense trees or a berm

with vegetation on top of it to create a vegetative barrier (Van Renterghem and

Botteldooren 2012) Advancements in environmentally-friendly vehicle technology have

also resulted in quieter cars (Komada and Yoshioka 2005) pushing this development into

trucking will have far-reaching effects As unlikely as it is reducing the speed limit in

critical habitat areas can reduce the noise levels from transportation considerably

Understanding how extremely threatened taxa like amphibians (McCallum 2009

Sep 2) respond to novel stressors such as anthropogenic noise can help us determine

better management and conservation methods From both this study and existing

literature on anthropogenic noise impacts on calling anurans it is clear that there is no

unifying strategy to compensate for masking and the reduction in communication space-

time While some species may show enough vocal plasticity to compensate for the

constraints of noise on their communication strategies (Cunnington and Fahrig 2010)

many other species may lack that mechanism and may therefore suffer more and need our

protection from noise pollution In the face of major threats such as climate change

disease and invasive species it is important to take into account other stressors which

may interact synergistically to best conserve amphibians worldwide

25

TABLES

Table 1 List of sites years recorded gain settings number of frogs (n) and number of recording nights (nights where directional recording took place)

26

Table 2 summary of parameters by site Mean recording distance is the average of the distance between the microphone and the frog recorded over all

recording sessions

27

Table 3 model statistics for call rate frequency duration and source level

28

Table 4 Radius and active communication space time (Time-area) related to noise level and call rate

29

FIGURES

Figure 1 sites used for analysis Year 1 Talking Water Gardens Finley Finger Bond Butte and Jackson

Frazier Year 2 all but Talking Water Gardens

30

Figure 2 a) 1-second spectrogram of a single Pacific chorus frog call b) 15-second spectrogram of road

noise in overlapping bandwidth of frog call

31

Figure 3 ambient road noise levels (dB re 20 micropa) per site against distance from busy road (km) (t6 = -633

p lt 0005)

32

Figure 4 confidence intervals of slope estimates for each parameter of interest

33

Figure 5 a) raw data of call rate against noise level color-coded by temperature b) raw data of call rate

between 9 and 12 degrees C against noise level with linear model c) predicted relationship of call rate

against noise level at each temperature (color-coded)

34

Figure 6 model of communication space-time for each site represented by the circles and their size as a

factor of distance from busy road and noise level Radius is measured in meters and call rate is measured in

calls per minute

35

CHAPTER 3 ndash Conclusions

We explored the impacts of road noise on Pacific chorus frog communication by

recording individual frogs and their respective soundscapes across a gradient of road

noise exposure generated by an interstate highway We used both passive acoustic

monitoring to document soundscapes as well as directional acoustic recording to quantify

parameters of interest (source level frequency call rate and call duration) in individual

calling male frogs No changes were observed in relation to noise for source level

frequency or call duration However we found that through masking and the reduction

of call rate at relatively high-noise sites communication space-time was dramatically

reduced for an individual calling frog

This study showed that chronic road noise does alter the vocalizations of even a

very generalist species to its detriment This has serious implications for mating success

in noisy areas as female frogs rely on cues within the malersquos call to assess mate fitness

Both females and males use calls from conspecifics to locate the breeding ponds

(Gerhardt and Huber 2002) a reduction in communication space-time entails a smaller

space and fewer opportunities for orientation and mate assessment While it is unclear

exactly how population dynamics could be impacted this shift in communication space-

time conservation efforts that have previously focused on other habitat aspects should

also consider the often-ignored soundscape Protection of communication space-time for

vocalizing Pacific chorus frogs through vegetation or man-made barriers could reverse

the call rate reduction and increase the space over which an individualrsquos call can be

heard while also providing the benefit of a quieter less anthropogenic-influenced

soundscape for all the other species within the habitat Indeed healthy soundscapes are

often a good indicator of ecosystem health in general (Pekin et al 2012) so listening may

be a cost-effective alternative to other forms of monitoring

This study suffered from several limitations and setbacks Initially we planned to

examine twelve sites divided into two groups near-highway and far-highway allowing

for a larger sample size within a given noise treatment However issues arose with the

disappearance of frog breeding from formerly robust near-highway sites between 2014

and 2015 The sites at which this occurred were Talking Water Gardens Ankeny Frog

Pond (the Ankeny site was moved across the road to Ankeny Wood Duck Pond) and a

36

Malpass Farms site that was not included in this analysis The reason for these

disappearances is unknown but is likely influenced by invasive American bullfrogs

(Lithobates catesbianus) Because of this sites were taken to be individual across a

gradient of noise exposure rather than within a group

Study of choruses as a whole was originally planned with data to be extracted

from passive acoustic monitoring We intended to examine the dominant frequency of the

chorus as a whole as well as chorus start and end time and compare across a gradient of

noise exposure This would have given us an idea of some of the social impacts of road

noise as well as other temporal effects such as shifting of chorus start or duration

However this proved to be impossible because the chorus data could not be extracted

from road noise through acoustic analysis or aural-visual assessment at sites with high

noise levels We anticipated this shift in chorus timing would coincide with a predictable

shift in road noise levels due to higher traffic levels at rush hour However this shift in

road noise levels was not seen on this particular highway system This may be because

the portion of Interstate 5 through the Willamette Valley has a more constant traffic

pattern than it would nearer an urban area such as Portland with a commuter presence

We also did not thoroughly examine population differences between sites which

may account for some of the differences we encountered During 2015 two-part visual

encounter surveys were performed for every night of directional recording following the

protocol outlined by Olson et al (1997) The first nightly survey was done during daylight

hours and consisted of a 30-minute visual encounter survey for Pacific chorus frog egg

masses only The second nightly survey was done just prior to the start of recording after

chorusing had begun and consisted of a 30-minute visual encounter survey for Pacific

chorus frog adults As animals were encountered they were captured if possible

weighed measured for snout-vent length and sexed If they were not captured they were

still recorded as being encountered with their behavior and substrate also noted This

visual survey data while valuable for a baseline and for training purposes was not

sufficient to quantify any differences in population structures or reproductive success

between sites

Additionally we did not take any data about the physical habitat aside from

temperature relative humidity and noise level we cannot therefore make any claim to

37

the causality of the shifts in vocalization behavior we saw We are unaware of any studies

on female perception in this species and we are therefore unable to say if the

implications for female performance are correct Further work needs to explore the

female side of noise impacts in anurans and document how they react to communication

signals and the reduction in active communication space-time in high-noise

environments

Lastly this study does not take into account any social effects such as chorusing

or male spacing Males were recorded in a chorus situation but the situation was not

standardized nor was inter-male spacing taken into account It may be that this species

shifts its call rate differently when in a dense chorus situation than when in a relatively

sparse chorus situation Future work should address these social influences as they have

been found to have large impacts on the behavior of calling males in other species of

anurans (Lengagne 2008)

This study lays the groundwork for further study into the impacts of road noise on

amphibians in the Pacific Northwest The relatively small number of above-water vocal

species in this area provides an ideal study system to further examine how road noise

impacts anuran frog vocalization communication fitness and reproductive success and

how noise compounds with other stressors such as habitat degradation and invasive

species Most studies of anthropogenic noise impacts including this one discuss the

implications of masking compensation (or lack thereof) on reproductive success

however very few actually demonstrate any evidence of tangible impact on populations

or communities

Continuing study of this system will involve examining those implications more

thoroughly It has already been established that road noise causes stress in vocal species

of frog (Tennessen and Parks 2014) and stress has been found to cause decreased growth

and immunosuppression in amphibians (Gabor Fisher et al 2013) By manipulating

noise levels in the lab we can further examine the relationship between noise and stress

hormones Further we can then use those results to investigate how stress hormones

impact reproductive success by looking at metrics of reproductive success such as sperm

motility in males and egg count in females These laboratory experiments can be

corroborated with observations in the field in order to determine if there is a population-

38

level impact on this species of high levels of noise Additionally we would like to

examine how noise may be compounded with other stressors such as invasive species

and if invasive species are more robust against the stress of noise than native species

Through this further study we hope to more thoroughly examine the impacts of

anthropogenic noise on population and community structure of anurans in the Pacific

Northwest

39

LITERATURE CITED

Allan D 1973 Some relationships of vocalization to behavior in the Pacific treefrog Hyla regilla Herpetologicandash

Bagwell C 2013 Sound eXchange

Barber JR Burdett CL Reed SE Warner KA Formichella C Crooks KR Theobald DM Fristrup KM 2011 Anthropogenic noise exposure in protected natural areas estimating the scale of ecological consequences Landscape Ecology 261281ndash1295

Barber JR Crooks KR Fristrup KM 2010 The costs of chronic noise exposure for terrestrial organisms Trends in Ecology amp Evolution 25180ndash189

Bee MA Schwartz JJ 2013 Anuran Acoustic Signal Production in Noisy Environments In Brumm H editor Animal Communication and Noise Berlin Heidelberg Springer Berlin Heidelberg

Bradbury JW Vehrencamp SL 2011 Principles of Animal Communication 2nd ed Sinauer Associates

Brattstrom BH Warren JW 1955 Observations on the Ecology and Behavior of the Pacific Treefrog Hyla regilla Copeia 1955181

Brumm H Todt D 2002 Noise-dependent song amplitude regulation in a territorial songbird Animal Behaviour 63891ndash897

Clark CW Ellison WT Southall BL Hatch LT 2009 Acoustic masking in marine ecosystems intuitions analysis and implication hellip Ecology Progress Series

Cocroft RB Ryan MJ 1995 Patterns of advertisement call evolution in toads and chorus frogs Animal Behaviour 49283ndash303

Cunnington GM Fahrig L 2010 Plasticity in the vocalizations of anurans in response to traffic noise Acta Oecologica 36463ndash470

Dumyahn SL Pijanowski BC 2011a Beyond noise mitigation managing soundscapes as common-pool resources Landscape Ecology1ndash16

Dumyahn SL Pijanowski BC 2011b Soundscape conservation Landscape Ecology 261327ndash1344

Embleton TFW 1996 Tutorial on sound propagation outdoors J Acoust Soc Am 10031ndash48

Forrest TG 1994 From Sender to Receiver Propagation and Environmental Effects on Acoustic Signals Amer Zool 34644ndash654

40

Gabor CR Bosch J Fries JN Davis DR 2013 A non-invasive water-borne hormone assay for amphibians Amphibia-Reptilia 34151ndash162

Gabor CR Fisher MC Bosch J 2013 A Non-Invasive Stress Assay Shows That Tadpole Populations Infected with Batrachochytrium dendrobatidis Have Elevated Corticosterone Levels PLoS ONE 8e56054

Gerhardt HC Bee MA 2007 Recognition and Localization of Acoustic Signals In Hearing and sound communication in amphibians

Gerhardt HC Huber F 2002 Acoustic communication in insects and anurans common problems and diverse solutions Chicago University of Chicago Press

Hage SR Jiang T Berquist SW Feng J Metzner W 2013 Ambient noise induces independent shifts in call frequency and amplitude within the Lombard effect in echolocating bats PNAS 1104063ndash4068

Herrera-Montes MI Aide TM 2011 Impacts of traffic noise on anuran and bird communities Urban Ecosyst

Holderied M Korine C Moritz T 2011 Hemprichrsquos long-eared bat (Otonycteris hemprichii) as a predator of scorpions whispering echolocation passive gleaning and prey selection J Comp Physiol A 197425ndash433

Holt MM Noren DP Veirs V Emmons CK Veirs S 2009 Speaking up Killer whales (Orcinus orca) increase their call amplitude in response to vessel noise J Acoust Soc Am 125EL27ndash6

Jones LLC Olson DH Seattle Audubon Society 2005 Amphibians of the Pacific Northwest Seattle WA Seattle Audubon Society

Kaiser K Hammers JL 2009 The effect of anthropogenic noise on male advertisement call rate in the neotropical treefrog Dendropsophus triangulum Behaviour

Komada M Yoshioka T 2005 Noise and Vibration Reduction Technology in New Generation Hybrid Vehicle Development NVC 12005ndash01ndash2294

Lengagne T 2008 Traffic noise affects communication behaviour in a breeding anuran Hyla arborea Biological Conservation

Leonard WP 1993 Amphibians of Washington and Oregon

Lewis ER Narins PM 1999 The Acoustic Periphery of Amphibians Anatomy and Physiology In Comparative Hearing Fish and Amphibians Vol 11 New York NY Springer New York (Springer Handbook of Auditory Research) pp 101ndash154 54 p

Lopez PT Narins PM Lewis ER Moore SW 1988 Acoustically induced call modification in the white-lipped frog Leptodactylus albilabris Animal Behaviour

41

361295ndash1308

Mason MJ 2007 Pathways for Sound Transmission to the Inner Ear in Amphibians In Narins PM Feng AS Fay RR Popper AN editors Hearing and sound communication in amphibians Springer New York

McCallum ML 2009 Sep 2 Amphibian Decline or Extinction Current Declines Dwarf Background Extinction Rate httpdxdoiorg1016700022-1511(2007)41[483ADOECD]20CO2

McGregor PK Leonard ML Horn AG Thomsen F 2013 Anthropogenic Noise and Conservation Brumm H editor Berlin Heidelberg Springer Berlin Heidelberg

Mellinger DK Bradbury JW 2007 Acoustic measurement of marine mammal sounds in noisy environments pp 273ndash280 8 p

Miller HJ 1999 Measuring Space-Time Accessibility Benefits within Transportation Networks Basic Theory and Computational Procedures Geographical Analysis 311ndash26

Narins PM 2007 Hearing and sound communication in amphibians

Nussbaum RA Brodie ED Jr Storm RM 1983 Amphibians and reptiles of the Pacific Northwest

Olson DH Leonard WP Bury RB 1997 Sampling amphibians in lentic habitats methods and approaches for the Pacific Northwest Society for Northwestern Vertebrate Biology

Pekin BK Jung J Villanueva-Rivera LJ Pijanowski BC Ahumada JA 2012 Modeling acoustic diversity using soundscape recordings and LIDAR-derived metrics of vertical forest structure in a neotropical rainforest Landscape Ecology 271513ndash1522

Pijanowski BC Farina A Gage SH Dumyahn SL Krause B 2011 What is soundscape ecology An introduction and overview of an emerging new science Landscape Ecology 261213ndash1232

Pijanowski BC Villanueva-Rivera LJ Dumyahn SL Farina A Krause B Napoletano BM Gage SH Pieretti N 2011 Soundscape Ecology The Science of Sound in the Landscape BioScience 61203ndash216

Pinheiro JC Bates DM 2015 Package nlme

Potvin DA MacDougall-Shackleton SA 2015 Sep 9 Traffic noise affects embryo mortality and nestling growth rates in captive zebra finches J Exp Zoolnandashna

R Core Team 2015 R A langauge and environment for statistical computing

Ridley AR Wiley EM Thompson AM 2014 The ecological benefits of interceptive

42

eavesdropping Funct Ecology 28197ndash205

Sanchez-Perez JV Rubio C Martinez-Sala R Sanchez-Grandia R Gomez V 2002 Acoustic barriers based on periodic arrays of scatterers Applied Physics Letters 815240ndash5242

Schaub D Larsen J Jr 1978 The reproductive ecology of the Pacific treefrog (Hyla regilla) Herpetologicandash

Schwartz JJ Gerhardt HC 1989 Spatially mediated release from auditory masking in an anuran amphibian J Comp Physiol A 16637ndash41

Slabbekoorn H 2003 Birds sing at a higher pitch in urban noise Nature

Slabbekoorn H Peet M 2003 Ecology Birds sing at a higher pitch in urban noise Nature 424267ndash267

Snyder WF Jameson DL 1965 Multivariate Geographic Variation of Mating Call in Populations of the Pacific Tree Frog (Hyla regilla) Copeia 1965129 [accessed 2014 Jul 2] httpwwwjstororgstable1440714origin=crossref

Sullivan BK Wagner WE join( 1988 Variation in Advertisement and Release Calls and Social Influences on Calling Behavior in the Gulf Coast Toad (Bufo valliceps) Copeia 19881014

Sun J Narins PM 2005 Anthropogenic sounds differentially affect amphibian call rate Biological Conservationndash

Tennessen JB Parks SE 2014 Traffic noise causes physiological stress and impairs breeding migration behaviour in frogs Conservation Physiology

Tucker D Gage SH Williamson I Fuller S 2014 Linking ecological condition and the soundscape in fragmented Australian forests Landscape Ecology 29745ndash758

Van Renterghem T Botteldooren D 2012 On the choice between walls and berms for road traffic noise shielding including wind effects Landscape and Urban Planning 105199ndash210

Velez A Bee MA 2011 Dip listening and the cocktail party problem in grey treefrogs signal recognition in temporally fluctuating noise Animal Behaviour 821319ndash1327

Ware HE McClure CJW Carlisle JD Barber JR 2015 Aug 31 A phantom road experiment reveals traffic noise is an invisible source of habitat degradation PNAS201504710ndash5

Wells KD Taigen TL OBrien JA 1996 The effect of temperature on calling energetics of the spring peeper (Pseudacris crucifer) Amphibia- hellip 17149ndash158

43

Wiley RH 2013 Signal Detection Noise and the Evolution of Communication In Brumm H editor Animal Communication and Noise Vol 2 Berlin Heidelberg Springer Berlin Heidelberg (Animal Signals and Communication) pp 7ndash30 24 p

Wollerman L Wiley RH 2002 Background noise from a natural chorus alters female discrimination of male calls in a Neotropical frog Animal Behaviour 6315ndash22

Wong B Cunningham RB Donnelly CF Cooper PD Do temperature and social environment interact to affect call rate in frogs (Crinia signifera) 2004

Zollinger SA Brumm H 2011 The Lombard effect Current Biology 21R614ndashR615

44


aurora

Danielle V Nelson Tiffany S Garcia Holger Klinck

45

ABSTRACT

Males of most anuran species use in-air acoustic communication to attract

females However the red-legged frog (Rana aurora) is one of few anuran species that

calls underwater making it difficult to survey using traditional visual and auditory

methods Red-legged frogs are experiencing significant population declines and are listed

as a vulnerable sensitive species in Oregon Uncertainty regarding basic life history

strategies is hindering effective management This study explored calling behavior and

breeding phenology by quantifying the seasonal and diel calling patterns of the red-

legged frog A passive acoustic recorder with hydrophone was used to capture

underwater anuran calls at Finley National Wildlife Refuge in Corvallis Oregon USA

Results suggest that red-legged frogs chorus from January until March for up to fourteen

hours at a time This is significantly longer in duration than previously recorded This

information will benefit management and conservation by better targeting species-

specific breeding strategies

46

INTRODUCTION

Many species of conservation concern live in areas that are difficult or impossible

to survey using conventional methods Without accurate monitoring techniques and

current information on distribution phenology and abundance effective management

can be challenging Amphibians are the most threatened group of vertebrates on the

planet (Blaustein Wake and Sousa 1994 Stuart et al 2004 Adams et al 2013) and are

often very difficult to monitor accurately They play a key role in many ecosystems as

both predators and prey and account for a considerable amount of biomass in terrestrial

and aquatic ecosystems (Blaustein Wake and Sousa 1994) Identifying accurate and

efficient amphibian monitoring strategies is essential for their conservation

Males of many species of anurans use vocalizations to attract females and to

establish territories within a breeding area (Gerhardt and Huber 2002) This

communication behavior can be extremely costly for the males some of which lose up to

40 of their body weight during the course of a breeding season (Gerhardt and Huber

2002) Females use cues in the calls of males to initiate breeding and to find a mate

(Gerhardt and Huber 2002 Bee and Schwartz 2013 Velez Bee and Schwartz 2013)

These vocalizations can be incredibly helpful in amphibian monitoring efforts and are

accurate indicators of both seasonal and diel breeding phenology

The red-legged frog (Rana aurora) is a semiaquatic frog and are one of the few

anurans that vocalizes underwater Traditional auditory survey methods are thus

ineffective with this species which ranges from northern California to British Columbia

and has a primarily coastal distribution (Jones Olson Seattle Audubon Society 2005) It

is a species of conservation concern in Oregon where its populations have been in

decline due to habitat loss land use change and invasive species (Kiesecker and

Blaustein 1998 Kiesecker and Blaustein 1997 Kiesecker Blaustein and Miller 2001)

While breeding behavior and life history have been described previously (Licht 1969

Storm 1960) very little is known about its communication behavior or breeding

phenology

Information on call dynamics and breeding phenology in this species is scarce

and has not been revisited since the late 1960rsquos Both Licht (1969) and Storm (1960)

described red-legged male vocalizations as a very quiet call which is heard over a two-

47

week breeding season Licht (1969) determined that the red-legged frog produces its

mating calls underwater a calling strategy which is relatively rare and restricted to a

closely related ranid group (Cascade frog R cascadae and the Foothill yellow-legged

frog (R boylii) in western America and some Xenopus species (Yager 1992 Hayes and

Krempels 1986) Further red-legged frogs typically breed in late winter to very early

spring (Storm 1960)

The predominant red-legged frog call has been previously described (Licht 1969)

and contains two to five individual syllables of increasing amplitude with a dominant

frequency between 450 and 1300 Hz It vocalizes primarily at night and begins its calling

after ambient air temperature have been above 5deg C for several days (Licht 1969)

However red-legged frog mating calls have not been thoroughly examined for structure

or diel and seasonal patterns

Understanding the communication behavior and breeding phenology of this

species is crucial to its conservation and management Passive acoustic monitoring has

been used across a wide variety of taxa to determine phenology occupancy and

communication behavior This technique is particularly useful in habitats where the

species is cryptic (Marques et al 2013) dispersed over a vast area (Stafford Fox and

Clark 1998) or other complications that make it difficult to monitor visually Passive

acoustic monitoring also allows for the continuous monitoring of vocal amphibian

species during the breeding season even when they are calling underwater

The aim of this pilot study was to examine the seasonal and diel calling behavior

of the red-legged frog (Rana aurora) using passive acoustics Specifically we wanted to

determine when vocalizations started and ended each day of the breeding season and the

total length of that season

METHODS

Data collection

A commercially available passive acoustic monitoring device (Song Meter SM2+

Wildlife Acoustics Inc Maynard MA USA) was installed at the edge of a freshwater

pond at Finley National Wildlife Refuge in Corvallis Oregon USA (44deg25358N

123deg193232W) The pond is a permanent water body with an average depth of 15

48

meters and is surrounded by agricultural lands primarily grass seed crops The recorder

was equipped with an omni-directional and pre-amplified HTI 96-min hydrophone (High

Tech Inc Long Beach MS USA) featuring a sensitivity of -165 dB re 1VmicroPa to

quantify the aquatic soundscape of the pond The incoming analog signal was high-pass

filtered at 180 Hz amplified with 36 dB digitized at 96 kHz and 16-bit resolution and

stored on 4x 128 GB SD memory cards The system had a flat response (3dB) in the

relevant frequency range of 200 Hz to 3000 Hz

The hydrophone was located approximately 2 meters from the shoreline at a water

depth of 1 meter This recorder was left in place to record continuously from January 31

to May 9 2014 these dates contain the previously determined red-legged breeding

season as well as most of the breeding season of sympatric native anurans Data

download and battery exchange happened every eleven days Temperature data was

recorded using an iButton temperature logger (Maxim Integrated San Jose CA USA)

programmed to take one reading every hour

Data analysis

After recovery of the instrument long-term spectral average (LTSA) plots were

created from the hydrophone data using the software Triton (Wiggins Roch and

Hildebrand 2010) Based on this information LTSAs were then examined visually and

aurally for evidence of red-legged frog calls as described in Licht (1969) Once

identified all instances of long-term chorusing were logged Daily sunrise and sunset

times as well as hourly air temperature (degrees C) were also recorded Data were

analyzed in R (R Core Team Vienna Austria httpwwwR-projectorg) for patterns of

vocalization including diel calling behavior influence of air temperature on overall

calling time and seasonal calling behavior Amount of calling per 24 hours was

measured in the time from 1200 to 1200 every day rather than 000 to 000 because of

the primarily nocturnal calling behavior of this species (Licht 1969)

RESULTS

The passive acoustic monitor recorded continuously from January 31 until May 5

2014 producing 99 days of acoustic data Of that period red-legged frog calls were

found on the hydrophone data on 32 days from January 31 to March 3

49

The median length of red-legged frog choruses was 7675 hours (IQR = 8169

hours Figure 1) The maximum amount of time spent chorusing in one 24-hour period

was 1412 hours Chorus start time appeared to be highly related to sunset time starting

on average 40 minutes after sunset each day (Figure 2) Chorus end time did not appear

to be strongly related to sunrise An example long-term spectral average (Figure 3) shows

an approximately 9-hour chorus from February 5-6 2014 which confirms the structure

previously defined by Licht as well as the amount of hours spent calling per day

Chorusing was already occurring on the day of installation of the passive acoustic

recorder January 31 and continued until March 3 a total of 32 days suggesting that the

breeding season lasts significantly longer than previously described in the literature (ie

two week period Licht 1969) Air temperature and calling duration and start time appear

to be highly correlated colder temperatures coincided with shorter chorus duration and

later start times (Figure 2)

DISCUSSION

We have demonstrated that there is a considerable amount of novel information

gained passive acoustic monitoring techniques Red-legged frogs were previously thought

to be explosive breeders with a relatively short two-week breeding period (Briggs 1987)

Storm (1960) documented the red-legged breeding season as approximately two weeks

while Licht (1969) found the breeding season at his two study sites to be 15 or 27 days

Here we recorded 32 days of mating calls and failed to get the initiation of breeding in

this population (ie breeding had already commenced at passive acoustic monitor

deployment) As such it is likely that the breeding season lasts longer than 32 days of

recording This indicates a more prolonged breeding season than originally documented

for this species Additionally given the energetic costs of calling for males a maximum

chorus duration of 14 hours is long in comparison to other species (Gerhardt and Huber

2002)

Interestingly we recorded two distinct periods of reduced calling (Figure 1)

These periods corresponded closely with two cold snaps during the winter of 2014 from

February 9 ndash 11 and February 15 ndash 18 when temperatures reached well below 0deg C This

corroborates Lichtrsquos (1969) assessment of the response of this species to low air

50

temperatures We also found that red-legged frog chorusing appears to be predominantly

nocturnal Most of the chorusing hours occurred after sunset and continued throughout

the night Only very rarely was a chorus found during daylight hours and this was

primarily when nighttime temperatures were very low for the area which further

demonstrates the relationship between chorusing and temperature

Aquatic amphibians are challenging to monitor since they are often cryptic and

difficult to detect via in-air acoustics As is often the case species that are difficult to

monitor are those with the most need of it especially since conservation status is often

inaccurate in the case of data-deficient species Our case study shows that passive

acoustic monitoring can provide valuable information on breeding behavior vocalization

and phenology in aquatic and semiaquatic species such as the red-legged frog This

technique has the potential to provide information about behavior phenology and

occupancy in the face of threats such as habitat loss global climate change and resulting

range shifts We found that a species of conservation concern in Oregon has a longer

breeding season than previously thought and that vocalizations are strongly tied to

temperature and time of day This information will help managersrsquo better limit

disturbances during breeding both seasonally and daily

In summary passive acoustic monitoring is a valuable tool for determining

phenology and occupancy with this species of aquatic-breeding frog It is unclear if these

data are indicative of the species as a whole or of only this local population further study

is needed to determine how these findings apply across populations and habitats More

work is also needed to determine call types and function as well as acoustic measures on

individual frogs This type of monitoring could easily be combined with a method such as

eDNA sampling (Lodge et al 2012) to gain an overall view of population structure in

breeding ponds without the need for visual surveying

ACKNOWLEDGEMENTS

The authors would like to thank S Fregosi for her help with fieldwork and S

Nieukirk for aiding in preparation of the manuscript Additionally we would like to

51

acknowledge the cooperation of the Willamette Valley National Wildlife Refuge

Complex and M Monroe for access to the study site

52

LITERATURE CITED

Adams M J D A W Miller E Muths P S Corn and E H C Grant 2013 Trends in Amphibian Occupancy in the United States PLOS One e64347

Bee M A and J J Schwartz 2013 Anuran Acoustic Signal Production in Noisy Environments In Animal Communication and Noise Henrik Brumm (ed) Springer Berlin Heidelberg Berlin Germany

Blaustein A R D B Wake and W P Sousa 1994 Amphibian Declines Judging Stability Persistence and Susceptibility of Populations to Local and Global Extinctions Conservation Biology 860mdash71

Briggs J L 1987 Breeding Biology of the Cascade Frog Rana cascadae with Comparisons to R aurora and R pretiosa Copeia 1987241mdash245

Gerhardt H C and F Huber 2002 Acoustic Communication in Insects and Anurans Common Problems and Diverse Solutions University of Chicago Press Chicago Illinois

Hayes M P and D M Krempels 1986 Vocal Sac Variation Among Frogs of the Genus Rana From Western North America Copeia 1986927mdash936

Jones L L Leonard W P amp Olson D H (Eds) 2005 Amphibians of the Pacific Northwest Seattle Audubon Society Seattle Washington

Kiesecker J M and A R Blaustein 1997 Population Differences in Responses of Red-Legged Frogs (Rana aurora) to Introduced Bullfrogs Ecology 781752mdash1760

Kiesecker J M and A R Blaustein 1998 Effects of Introduced Bullfrogs and Smallmouth Bass on Microhabitat Use Growth and Survival of Native Red‐Legged Frogs (Rana aurora) Conservation Biology 12776mdash787

Kiesecker J M A R Blaustein and C L Miller 2001 Potential Mechanisms Underlying the Displacement of Native Red-Legged Frogs by Introduced Bullfrogs Ecology 821964mdash1970

Licht L E 1969 Comparative Breeding Behavior of the Red-Legged Frog (Rana aurora aurora) and the Western Spotted Frog (Rana pretiosa pretiosa) in Southwestern British Columbia Canadian Journal of Zoology 471287mdash1299

Lodge D M C R Turner C L Jerde M A Barnes L Chadderton S P Egan J L Feder A R Mahon and M E Pfrender 2012 Conservation in a Cup of Water Estimating Biodiversity and Population Abundance From Environmental DNA Molecular Ecology 212555mdash2558

Marques T A L Thomas S W Martin D K Mellinger J A Ward D J Moretti D Harris and P L Tyack 2013 Estimating Animal Population Density Using Passive

53

Acoustics Biological Reviews 88287mdash309

Stafford K M C G Fox and D S Clark 1998 Long-Range Acoustic Detection and Localization of Blue Whale Calls in the Northeast Pacific Ocean The Journal of the Acoustical Society of America 1043616mdash3625

Storm R M 1960 Notes on the Breeding Biology of the Red-Legged Frog (Rana aurora) Herpetologica 16251mdash259

Stuart S N J S Chanson N A Cox B E Young A S L Rodrigues D L Fischman and R W Waller 2004 Status and Trends of Amphibian Declines and Extinctions Worldwide Science 3061783mdash1786

Velez A M A Bee and J J Schwartz 2013 Anuran Acoustic Signal Perception in Noisy Environments In Animal Communication and Noise Henrik Brumm (ed) Springer Berlin Heidelberg Berlin Germany

Wiggins S M M A Roch and J A Hildebrand 2010 TRITON Software Package Analyzing Large Passive Acoustic Monitoring Data Sets Using MATLAB The Journal of the Acoustical Society of America 1282299mdash2299

Yager D D 1992 Underwater Acoustic Communication in the African Pipid Frog Xenopus borealis Bioacoustics 41mdash24

54

FIGURES

Figure 7 Total daily hours spent calling 1200-1200 Line indicates the median 7675 hours per 24-hour

period Blue line indicates temperature in degrees C

55

Figure 8 Time of chorus start as difference from sunset (median = 67 h dotted line) Shaded area indicates

hours after sunset unshaded area indicates daylight hours Blue line indicates temperature in degrees C

56

Figure 9 Long-term spectral average (LTSA) plot of Finley Office Pond underwater soundscape recorded

on February 5 2014 at 0200 UTC (upper panel) Spectrogram showing individual red-legged frog calls

(lower panel)










December 7 2015

All Rights Reserved


COMMUNICATION

by

Danielle V Nelson

A THESIS

submitted to




degree of

Master of Science




APPROVED






upon request

`


ACKNOWLEDGEMENTS










































many many things





with her














TABLE OF CONTENTS

Page




ABSTRACT9

INTRODUCTION 10

METHODS 13

Field methods13




RESULTS 18


Call structure 18


DISCUSSION19

TABLES 25


LITERATURE CITED 39


aurora 44

ABSTRACT45

INTRODUCTION 46

METHODS 47

Data collection 47

Data analysis 48

RESULTS 48

DISCUSSION49

ACKNOWLEDGEMENTS50

LITERATURE CITED 52
















DEDICATION




1


SOUNDSCAPES

























2
































3
































4




FROG COMMUNICATION



















noise








5






Vocal production


























6































7



















RESEARCH QUESTIONS











8





9

ABSTRACT


























10

INTRODUCTION






























11
































12
















communication















13

METHODS

Field methods




















(Table 1)








14































15





























16
































17





























18










$012341 = 055-21(78-9) Equation 2

RESULTS












the sites

Call structure




19


























3)

DISCUSSION

20
































21































22
































23
































24





























25

TABLES


26


recording sessions

27


28


29

FIGURES



30



31


p lt 0005)

32


33




34



calls per minute

35
































36





























between sites



37






environments
















or communities










38






Northwest

39

LITERATURE CITED
















40
















41

361295ndash1308
















42
















43





44


aurora


45

ABSTRACT














46

INTRODUCTION



























phenology




47






spring (Storm 1960)



















METHODS

Data collection





48















Data analysis












RESULTS




49














DISCUSSION












2002)





50


























ACKNOWLEDGEMENTS



51



52

LITERATURE CITED














53








54

FIGURES



55



56



(lower panel)


December 7 2015

All Rights Reserved


COMMUNICATION

by

Danielle V Nelson

A THESIS

submitted to




degree of

Master of Science




APPROVED






upon request

`


ACKNOWLEDGEMENTS










































many many things





with her














TABLE OF CONTENTS

Page




ABSTRACT9

INTRODUCTION 10

METHODS 13

Field methods13




RESULTS 18


Call structure 18


DISCUSSION19

TABLES 25


LITERATURE CITED 39


aurora 44

ABSTRACT45

INTRODUCTION 46

METHODS 47

Data collection 47

Data analysis 48

RESULTS 48

DISCUSSION49

ACKNOWLEDGEMENTS50

LITERATURE CITED 52
















DEDICATION




1


SOUNDSCAPES

























2
































3
































4




FROG COMMUNICATION



















noise








5






Vocal production


























6































7



















RESEARCH QUESTIONS











8





9

ABSTRACT


























10

INTRODUCTION






























11
































12
















communication















13

METHODS

Field methods




















(Table 1)








14































15





























16
































17





























18










$012341 = 055-21(78-9) Equation 2

RESULTS












the sites

Call structure




19


























3)

DISCUSSION

20
































21































22
































23
































24





























25

TABLES


26


recording sessions

27


28


29

FIGURES



30



31


p lt 0005)

32


33




34



calls per minute

35
































36





























between sites



37






environments
















or communities










38






Northwest

39

LITERATURE CITED
















40
















41

361295ndash1308
















42
















43





44


aurora


45

ABSTRACT














46

INTRODUCTION



























phenology




47






spring (Storm 1960)



















METHODS

Data collection





48















Data analysis












RESULTS




49














DISCUSSION












2002)





50


























ACKNOWLEDGEMENTS



51



52

LITERATURE CITED














53








54

FIGURES



55



56



(lower panel)


COMMUNICATION

by

Danielle V Nelson

A THESIS

submitted to




degree of

Master of Science




APPROVED






upon request

`


ACKNOWLEDGEMENTS










































many many things





with her














TABLE OF CONTENTS

Page




ABSTRACT9

INTRODUCTION 10

METHODS 13

Field methods13




RESULTS 18


Call structure 18


DISCUSSION19

TABLES 25


LITERATURE CITED 39


aurora 44

ABSTRACT45

INTRODUCTION 46

METHODS 47

Data collection 47

Data analysis 48

RESULTS 48

DISCUSSION49

ACKNOWLEDGEMENTS50

LITERATURE CITED 52
















DEDICATION




1


SOUNDSCAPES

























2
































3
































4




FROG COMMUNICATION



















noise








5






Vocal production


























6































7



















RESEARCH QUESTIONS











8





9

ABSTRACT


























10

INTRODUCTION






























11
































12
















communication















13

METHODS

Field methods




















(Table 1)








14































15





























16
































17





























18










$012341 = 055-21(78-9) Equation 2

RESULTS












the sites

Call structure




19


























3)

DISCUSSION

20
































21































22
































23
































24





























25

TABLES


26


recording sessions

27


28


29

FIGURES



30



31


p lt 0005)

32


33




34



calls per minute

35
































36





























between sites



37






environments
















or communities










38






Northwest

39

LITERATURE CITED
















40
















41

361295ndash1308
















42
















43





44


aurora


45

ABSTRACT














46

INTRODUCTION



























phenology




47






spring (Storm 1960)



















METHODS

Data collection





48















Data analysis












RESULTS




49














DISCUSSION












2002)





50


























ACKNOWLEDGEMENTS



51



52

LITERATURE CITED














53








54

FIGURES



55



56



(lower panel)


APPROVED






upon request

`


ACKNOWLEDGEMENTS










































many many things





with her














TABLE OF CONTENTS

Page




ABSTRACT9

INTRODUCTION 10

METHODS 13

Field methods13




RESULTS 18


Call structure 18


DISCUSSION19

TABLES 25


LITERATURE CITED 39


aurora 44

ABSTRACT45

INTRODUCTION 46

METHODS 47

Data collection 47

Data analysis 48

RESULTS 48

DISCUSSION49

ACKNOWLEDGEMENTS50

LITERATURE CITED 52
















DEDICATION




1


SOUNDSCAPES

























2
































3
































4




FROG COMMUNICATION



















noise








5






Vocal production


























6































7



















RESEARCH QUESTIONS











8





9

ABSTRACT


























10

INTRODUCTION






























11
































12
















communication















13

METHODS

Field methods




















(Table 1)








14































15





























16
































17





























18










$012341 = 055-21(78-9) Equation 2

RESULTS












the sites

Call structure




19


























3)

DISCUSSION

20
































21































22
































23
































24





























25

TABLES


26


recording sessions

27


28


29

FIGURES



30



31


p lt 0005)

32


33




34



calls per minute

35
































36





























between sites



37






environments
















or communities










38






Northwest

39

LITERATURE CITED
















40
















41

361295ndash1308
















42
















43





44


aurora


45

ABSTRACT














46

INTRODUCTION



























phenology




47






spring (Storm 1960)



















METHODS

Data collection





48















Data analysis












RESULTS




49














DISCUSSION












2002)





50


























ACKNOWLEDGEMENTS



51



52

LITERATURE CITED














53








54

FIGURES



55



56



(lower panel)

ACKNOWLEDGEMENTS










































many many things





with her














TABLE OF CONTENTS

Page




ABSTRACT9

INTRODUCTION 10

METHODS 13

Field methods13




RESULTS 18


Call structure 18


DISCUSSION19

TABLES 25


LITERATURE CITED 39


aurora 44

ABSTRACT45

INTRODUCTION 46

METHODS 47

Data collection 47

Data analysis 48

RESULTS 48

DISCUSSION49

ACKNOWLEDGEMENTS50

LITERATURE CITED 52
















DEDICATION




1


SOUNDSCAPES

























2
































3
































4




FROG COMMUNICATION



















noise








5






Vocal production


























6































7



















RESEARCH QUESTIONS











8





9

ABSTRACT


























10

INTRODUCTION






























11
































12
















communication















13

METHODS

Field methods




















(Table 1)








14































15





























16
































17





























18










$012341 = 055-21(78-9) Equation 2

RESULTS












the sites

Call structure




19


























3)

DISCUSSION

20
































21































22
































23
































24





























25

TABLES


26


recording sessions

27


28


29

FIGURES



30



31


p lt 0005)

32


33




34



calls per minute

35
































36





























between sites



37






environments
















or communities










38






Northwest

39

LITERATURE CITED
















40
















41

361295ndash1308
















42
















43





44


aurora


45

ABSTRACT














46

INTRODUCTION



























phenology




47






spring (Storm 1960)



















METHODS

Data collection





48















Data analysis












RESULTS




49














DISCUSSION












2002)





50


























ACKNOWLEDGEMENTS



51



52

LITERATURE CITED














53








54

FIGURES



55



56



(lower panel)













many many things





with her














TABLE OF CONTENTS

Page




ABSTRACT9

INTRODUCTION 10

METHODS 13

Field methods13




RESULTS 18


Call structure 18


DISCUSSION19

TABLES 25


LITERATURE CITED 39


aurora 44

ABSTRACT45

INTRODUCTION 46

METHODS 47

Data collection 47

Data analysis 48

RESULTS 48

DISCUSSION49

ACKNOWLEDGEMENTS50

LITERATURE CITED 52
















DEDICATION




1


SOUNDSCAPES

























2
































3
































4




FROG COMMUNICATION



















noise








5






Vocal production


























6































7



















RESEARCH QUESTIONS











8





9

ABSTRACT


























10

INTRODUCTION






























11
































12
















communication















13

METHODS

Field methods




















(Table 1)








14































15





























16
































17





























18










$012341 = 055-21(78-9) Equation 2

RESULTS












the sites

Call structure




19


























3)

DISCUSSION

20
































21































22
































23
































24





























25

TABLES


26


recording sessions

27


28


29

FIGURES



30



31


p lt 0005)

32


33




34



calls per minute

35
































36





























between sites



37






environments
















or communities










38






Northwest

39

LITERATURE CITED
















40
















41

361295ndash1308
















42
















43





44


aurora


45

ABSTRACT














46

INTRODUCTION



























phenology




47






spring (Storm 1960)



















METHODS

Data collection





48















Data analysis












RESULTS




49














DISCUSSION












2002)





50


























ACKNOWLEDGEMENTS



51



52

LITERATURE CITED














53








54

FIGURES



55



56



(lower panel)







TABLE OF CONTENTS

Page




ABSTRACT9

INTRODUCTION 10

METHODS 13

Field methods13




RESULTS 18


Call structure 18


DISCUSSION19

TABLES 25


LITERATURE CITED 39


aurora 44

ABSTRACT45

INTRODUCTION 46

METHODS 47

Data collection 47

Data analysis 48

RESULTS 48

DISCUSSION49

ACKNOWLEDGEMENTS50

LITERATURE CITED 52
















DEDICATION




1


SOUNDSCAPES

























2
































3
































4




FROG COMMUNICATION



















noise








5






Vocal production


























6































7



















RESEARCH QUESTIONS











8





9

ABSTRACT


























10

INTRODUCTION






























11
































12
















communication















13

METHODS

Field methods




















(Table 1)








14































15





























16
































17





























18










$012341 = 055-21(78-9) Equation 2

RESULTS












the sites

Call structure




19


























3)

DISCUSSION

20
































21































22
































23
































24





























25

TABLES


26


recording sessions

27


28


29

FIGURES



30



31


p lt 0005)

32


33




34



calls per minute

35
































36





























between sites



37






environments
















or communities










38






Northwest

39

LITERATURE CITED
















40
















41

361295ndash1308
















42
















43





44


aurora


45

ABSTRACT














46

INTRODUCTION



























phenology




47






spring (Storm 1960)



















METHODS

Data collection





48















Data analysis












RESULTS




49














DISCUSSION












2002)





50


























ACKNOWLEDGEMENTS



51



52

LITERATURE CITED














53








54

FIGURES



55



56



(lower panel)

TABLE OF CONTENTS

Page




ABSTRACT9

INTRODUCTION 10

METHODS 13

Field methods13




RESULTS 18


Call structure 18


DISCUSSION19

TABLES 25


LITERATURE CITED 39


aurora 44

ABSTRACT45

INTRODUCTION 46

METHODS 47

Data collection 47

Data analysis 48

RESULTS 48

DISCUSSION49

ACKNOWLEDGEMENTS50

LITERATURE CITED 52
















DEDICATION




1


SOUNDSCAPES

























2
































3
































4




FROG COMMUNICATION



















noise








5






Vocal production


























6































7



















RESEARCH QUESTIONS











8





9

ABSTRACT


























10

INTRODUCTION






























11
































12
















communication















13

METHODS

Field methods




















(Table 1)








14































15





























16
































17





























18










$012341 = 055-21(78-9) Equation 2

RESULTS












the sites

Call structure




19


























3)

DISCUSSION

20
































21































22
































23
































24





























25

TABLES


26


recording sessions

27


28


29

FIGURES



30



31


p lt 0005)

32


33




34



calls per minute

35
































36





























between sites



37






environments
















or communities










38






Northwest

39

LITERATURE CITED
















40
















41

361295ndash1308
















42
















43





44


aurora


45

ABSTRACT














46

INTRODUCTION



























phenology




47






spring (Storm 1960)



















METHODS

Data collection





48















Data analysis












RESULTS




49














DISCUSSION












2002)





50


























ACKNOWLEDGEMENTS



51



52

LITERATURE CITED














53








54

FIGURES



55



56



(lower panel)

DISCUSSION49

ACKNOWLEDGEMENTS50

LITERATURE CITED 52
















DEDICATION




1


SOUNDSCAPES

























2
































3
































4




FROG COMMUNICATION



















noise








5






Vocal production


























6































7



















RESEARCH QUESTIONS











8





9

ABSTRACT


























10

INTRODUCTION






























11
































12
















communication















13

METHODS

Field methods




















(Table 1)








14































15





























16
































17





























18










$012341 = 055-21(78-9) Equation 2

RESULTS












the sites

Call structure




19


























3)

DISCUSSION

20
































21































22
































23
































24





























25

TABLES


26


recording sessions

27


28


29

FIGURES



30



31


p lt 0005)

32


33




34



calls per minute

35
































36





























between sites



37






environments
















or communities










38






Northwest

39

LITERATURE CITED
















40
















41

361295ndash1308
















42
















43





44


aurora


45

ABSTRACT














46

INTRODUCTION



























phenology




47






spring (Storm 1960)



















METHODS

Data collection





48















Data analysis












RESULTS




49














DISCUSSION












2002)





50


























ACKNOWLEDGEMENTS



51



52

LITERATURE CITED














53








54

FIGURES



55



56



(lower panel)
















DEDICATION




1


SOUNDSCAPES

























2
































3
































4




FROG COMMUNICATION



















noise








5






Vocal production


























6































7



















RESEARCH QUESTIONS











8





9

ABSTRACT


























10

INTRODUCTION






























11
































12
















communication















13

METHODS

Field methods




















(Table 1)








14































15





























16
































17





























18










$012341 = 055-21(78-9) Equation 2

RESULTS












the sites

Call structure




19


























3)

DISCUSSION

20
































21































22
































23
































24





























25

TABLES


26


recording sessions

27


28


29

FIGURES



30



31


p lt 0005)

32


33




34



calls per minute

35
































36





























between sites



37






environments
















or communities










38






Northwest

39

LITERATURE CITED
















40
















41

361295ndash1308
















42
















43





44


aurora


45

ABSTRACT














46

INTRODUCTION



























phenology




47






spring (Storm 1960)



















METHODS

Data collection





48















Data analysis












RESULTS




49














DISCUSSION












2002)





50


























ACKNOWLEDGEMENTS



51



52

LITERATURE CITED














53








54

FIGURES



55



56



(lower panel)






DEDICATION




1


SOUNDSCAPES

























2
































3
































4




FROG COMMUNICATION



















noise








5






Vocal production


























6































7



















RESEARCH QUESTIONS











8





9

ABSTRACT


























10

INTRODUCTION






























11
































12
















communication















13

METHODS

Field methods




















(Table 1)








14































15





























16
































17





























18










$012341 = 055-21(78-9) Equation 2

RESULTS












the sites

Call structure




19


























3)

DISCUSSION

20
































21































22
































23
































24





























25

TABLES


26


recording sessions

27


28


29

FIGURES



30



31


p lt 0005)

32


33




34



calls per minute

35
































36





























between sites



37






environments
















or communities










38






Northwest

39

LITERATURE CITED
















40
















41

361295ndash1308
















42
















43





44


aurora


45

ABSTRACT














46

INTRODUCTION



























phenology




47






spring (Storm 1960)



















METHODS

Data collection





48















Data analysis












RESULTS




49














DISCUSSION












2002)





50


























ACKNOWLEDGEMENTS



51



52

LITERATURE CITED














53








54

FIGURES



55



56



(lower panel)

DEDICATION




1


SOUNDSCAPES

























2
































3
































4




FROG COMMUNICATION



















noise








5






Vocal production


























6































7



















RESEARCH QUESTIONS











8





9

ABSTRACT


























10

INTRODUCTION






























11
































12
















communication















13

METHODS

Field methods




















(Table 1)








14































15





























16
































17





























18










$012341 = 055-21(78-9) Equation 2

RESULTS












the sites

Call structure




19


























3)

DISCUSSION

20
































21































22
































23
































24





























25

TABLES


26


recording sessions

27


28


29

FIGURES



30



31


p lt 0005)

32


33




34



calls per minute

35
































36





























between sites



37






environments
















or communities










38






Northwest

39

LITERATURE CITED
















40
















41

361295ndash1308
















42
















43





44


aurora


45

ABSTRACT














46

INTRODUCTION



























phenology




47






spring (Storm 1960)



















METHODS

Data collection





48















Data analysis












RESULTS




49














DISCUSSION












2002)





50


























ACKNOWLEDGEMENTS



51



52

LITERATURE CITED














53








54

FIGURES



55



56



(lower panel)

1


SOUNDSCAPES

























2
































3
































4




FROG COMMUNICATION



















noise








5






Vocal production


























6































7



















RESEARCH QUESTIONS











8





9

ABSTRACT


























10

INTRODUCTION






























11
































12
















communication















13

METHODS

Field methods




















(Table 1)








14































15





























16
































17





























18










$012341 = 055-21(78-9) Equation 2

RESULTS












the sites

Call structure




19


























3)

DISCUSSION

20
































21































22
































23
































24





























25

TABLES


26


recording sessions

27


28


29

FIGURES



30



31


p lt 0005)

32


33




34



calls per minute

35
































36





























between sites



37






environments
















or communities










38






Northwest

39

LITERATURE CITED
















40
















41

361295ndash1308
















42
















43





44


aurora


45

ABSTRACT














46

INTRODUCTION



























phenology




47






spring (Storm 1960)



















METHODS

Data collection





48















Data analysis












RESULTS




49














DISCUSSION












2002)





50


























ACKNOWLEDGEMENTS



51



52

LITERATURE CITED














53








54

FIGURES



55



56



(lower panel)

2
































3
































4




FROG COMMUNICATION



















noise








5






Vocal production


























6































7



















RESEARCH QUESTIONS











8





9

ABSTRACT


























10

INTRODUCTION






























11
































12
















communication















13

METHODS

Field methods




















(Table 1)








14































15





























16
































17





























18










$012341 = 055-21(78-9) Equation 2

RESULTS












the sites

Call structure




19


























3)

DISCUSSION

20
































21































22
































23
































24





























25

TABLES


26


recording sessions

27


28


29

FIGURES



30



31


p lt 0005)

32


33




34



calls per minute

35
































36





























between sites



37






environments
















or communities










38






Northwest

39

LITERATURE CITED
















40
















41

361295ndash1308
















42
















43





44


aurora


45

ABSTRACT














46

INTRODUCTION



























phenology




47






spring (Storm 1960)



















METHODS

Data collection





48















Data analysis












RESULTS




49














DISCUSSION












2002)





50


























ACKNOWLEDGEMENTS



51



52

LITERATURE CITED














53








54

FIGURES



55



56



(lower panel)

3
































4




FROG COMMUNICATION



















noise








5






Vocal production


























6































7



















RESEARCH QUESTIONS











8





9

ABSTRACT


























10

INTRODUCTION






























11
































12
















communication















13

METHODS

Field methods




















(Table 1)








14































15





























16
































17





























18










$012341 = 055-21(78-9) Equation 2

RESULTS












the sites

Call structure




19


























3)

DISCUSSION

20
































21































22
































23
































24





























25

TABLES


26


recording sessions

27


28


29

FIGURES



30



31


p lt 0005)

32


33




34



calls per minute

35
































36





























between sites



37






environments
















or communities










38






Northwest

39

LITERATURE CITED
















40
















41

361295ndash1308
















42
















43





44


aurora


45

ABSTRACT














46

INTRODUCTION



























phenology




47






spring (Storm 1960)



















METHODS

Data collection





48















Data analysis












RESULTS




49














DISCUSSION












2002)





50


























ACKNOWLEDGEMENTS



51



52

LITERATURE CITED














53








54

FIGURES



55



56



(lower panel)

4




FROG COMMUNICATION



















noise








5






Vocal production


























6































7



















RESEARCH QUESTIONS











8





9

ABSTRACT


























10

INTRODUCTION






























11
































12
















communication















13

METHODS

Field methods




















(Table 1)








14































15





























16
































17





























18










$012341 = 055-21(78-9) Equation 2

RESULTS












the sites

Call structure




19


























3)

DISCUSSION

20
































21































22
































23
































24





























25

TABLES


26


recording sessions

27


28


29

FIGURES



30



31


p lt 0005)

32


33




34



calls per minute

35
































36





























between sites



37






environments
















or communities










38






Northwest

39

LITERATURE CITED
















40
















41

361295ndash1308
















42
















43





44


aurora


45

ABSTRACT














46

INTRODUCTION



























phenology




47






spring (Storm 1960)



















METHODS

Data collection





48















Data analysis












RESULTS




49














DISCUSSION












2002)





50


























ACKNOWLEDGEMENTS



51



52

LITERATURE CITED














53








54

FIGURES



55



56



(lower panel)

5






Vocal production


























6































7



















RESEARCH QUESTIONS











8





9

ABSTRACT


























10

INTRODUCTION






























11
































12
















communication















13

METHODS

Field methods




















(Table 1)








14































15





























16
































17





























18










$012341 = 055-21(78-9) Equation 2

RESULTS












the sites

Call structure




19


























3)

DISCUSSION

20
































21































22
































23
































24





























25

TABLES


26


recording sessions

27


28


29

FIGURES



30



31


p lt 0005)

32


33




34



calls per minute

35
































36





























between sites



37






environments
















or communities










38






Northwest

39

LITERATURE CITED
















40
















41

361295ndash1308
















42
















43





44


aurora


45

ABSTRACT














46

INTRODUCTION



























phenology




47






spring (Storm 1960)



















METHODS

Data collection





48















Data analysis












RESULTS




49














DISCUSSION












2002)





50


























ACKNOWLEDGEMENTS



51



52

LITERATURE CITED














53








54

FIGURES



55



56



(lower panel)

6































7



















RESEARCH QUESTIONS











8





9

ABSTRACT


























10

INTRODUCTION






























11
































12
















communication















13

METHODS

Field methods




















(Table 1)








14































15





























16
































17





























18










$012341 = 055-21(78-9) Equation 2

RESULTS












the sites

Call structure




19


























3)

DISCUSSION

20
































21































22
































23
































24





























25

TABLES


26


recording sessions

27


28


29

FIGURES



30



31


p lt 0005)

32


33




34



calls per minute

35
































36





























between sites



37






environments
















or communities










38






Northwest

39

LITERATURE CITED
















40
















41

361295ndash1308
















42
















43





44


aurora


45

ABSTRACT














46

INTRODUCTION



























phenology




47






spring (Storm 1960)



















METHODS

Data collection





48















Data analysis












RESULTS




49














DISCUSSION












2002)





50


























ACKNOWLEDGEMENTS



51



52

LITERATURE CITED














53








54

FIGURES



55



56



(lower panel)

7



















RESEARCH QUESTIONS











8





9

ABSTRACT


























10

INTRODUCTION






























11
































12
















communication















13

METHODS

Field methods




















(Table 1)








14































15





























16
































17





























18










$012341 = 055-21(78-9) Equation 2

RESULTS












the sites

Call structure




19


























3)

DISCUSSION

20
































21































22
































23
































24





























25

TABLES


26


recording sessions

27


28


29

FIGURES



30



31


p lt 0005)

32


33




34



calls per minute

35
































36





























between sites



37






environments
















or communities










38






Northwest

39

LITERATURE CITED
















40
















41

361295ndash1308
















42
















43





44


aurora


45

ABSTRACT














46

INTRODUCTION



























phenology




47






spring (Storm 1960)



















METHODS

Data collection





48















Data analysis












RESULTS




49














DISCUSSION












2002)





50


























ACKNOWLEDGEMENTS



51



52

LITERATURE CITED














53








54

FIGURES



55



56



(lower panel)

8





9

ABSTRACT


























10

INTRODUCTION






























11
































12
















communication















13

METHODS

Field methods




















(Table 1)








14































15





























16
































17





























18










$012341 = 055-21(78-9) Equation 2

RESULTS












the sites

Call structure




19


























3)

DISCUSSION

20
































21































22
































23
































24





























25

TABLES


26


recording sessions

27


28


29

FIGURES



30



31


p lt 0005)

32


33




34



calls per minute

35
































36





























between sites



37






environments
















or communities










38






Northwest

39

LITERATURE CITED
















40
















41

361295ndash1308
















42
















43





44


aurora


45

ABSTRACT














46

INTRODUCTION



























phenology




47






spring (Storm 1960)



















METHODS

Data collection





48















Data analysis












RESULTS




49














DISCUSSION












2002)





50


























ACKNOWLEDGEMENTS



51



52

LITERATURE CITED














53








54

FIGURES



55



56



(lower panel)

Documents

The Effects of Road Noise on Pacific Chorus Frog Communication