BIRDS AND BURROWS: AVIFAUNA USE AND VISITATION OF … · BIRDS AND BURROWS: AVIFAUNA USE AND VISITATION OF BURROWS OF GOPHER TORTOISES AT TWO MILITARY SITES IN THE FLORIDA PANHANDLE

The Wilson Journal of Ornithology 129(4):792–803, 2017

BIRDS AND BURROWS: AVIFAUNA USE AND VISITATION OF

BURROWS OF GOPHER TORTOISES AT TWO MILITARY SITES IN

THE FLORIDA PANHANDLE

K. NICOLE WHITE1,2,3 AND TRACEY D. TUBERVILLE1

ABSTRACT.—The United States Department of Defense (DoD) has a dual mission of maintaining military readiness and

stewardship of its natural resources. The DoD invests more than $334 million on land and species management on their

properties, which support high levels of biodiversity and harbor a disproportionate number of threatened, endangered, and at-

risk species. The gopher tortoise (Gopherus polyphemus) occurs on 28 DoD installations in the southeastern United States.

Because more than 350 species have been documented to use their burrows, the gopher tortoise is considered a keystone

species. However, few species of birds have previously been documented as burrow associates. In this study, we compare

bird species richness, visitation frequency, and behaviors at gopher tortoise burrows at two Department of Navy properties

(Santa Rosa County, Florida) that differed in size, training intensity, habitat diversity, and proportion of habitat suitable for

gopher tortoises. We detected a total of 33 species of birds and documented previously unreported behaviors of foraging, dust

bathing, and wing-flashing display behaviors at tortoise burrows. Although species richness between sites was not

significantly different, frequency of visitation was greater at the site with less military training activity. Our findings

underscore the importance of even small military installations in supporting local biodiversity and the need to further explore

gopher tortoise burrows as a potential resource for avifauna. Received 23 August 2016. Accepted 4 February 2017.

Key words: avifauna, burrow associate, camera trap, Gopherus polyphemus, species richness.

Ecosystem management and biodiversity con-

servation are part of the mission of the United

States Department of Defense (DoD; Boice 1999).

The DoD manages .12 million ha. Although

these holdings represent only 3% of all federally

owned lands in the United States, densities of

endangered and threatened species are three times

higher on military lands compared to other federal

lands (Stein et al. 2008). An estimated 250

installations support at least one federally-listed

species and .375 installations are considered to

harbor ‘significant natural resources’ (Boice 2006).

The high biodiversity often associated with

military lands has been attributed to limited human

access and protection from development (Boice

2006), as well as the heterogeneous disturbance

regime resulting from spatial variation in training

intensities within installations (Warren et al. 2007).

In addition to supporting high levels of

biodiversity, DoD lands are frequently identified

as having a critical role in conservation and

recovery of individual rare or at-risk species, such

as the Red-cockaded Woodpecker (Picoides bor-

ealis; USFWS 2003) and the gopher tortoise

(Gopherus polyphemus; USFWS 2011, 2013).

The gopher tortoise—an iconic species of the

longleaf pine ecosystem—has been documented

on at least 28 military installations within its range

in the southeastern United States (Wilson et al.

1997). It occupies open canopy sites with deep

sandy soils in which it constructs its own burrows.

The burrow and its apron (the loose mound of sand

at the burrow entrance) provide tortoises a site for

foraging, reproduction, and refuge from fire,

predators, and thermal extremes (Jackson and

Milstrey 1989, Pike and Mitchell 2013). Because

their burrows are used by more than 65 vertebrate

and 300 invertebrate species, gopher tortoises are

considered both a keystone species (Eisenberg

1983, Catano and Stout 2015) and ecosystem

engineer (as defined by Jones et al. 1997, Kinlaw

and Grasmueck 2012, Pike and Mitchell 2013).

Previous studies have documented a variety of

vertebrates at tortoise burrows, although disruptive

sampling protocols, such as live trapping and

scoping with burrow cameras, have taxonomically

biased observations towards non-avian species

(Frank and Lips 1989, Lips 1991, Knizley 1997),

likely resulting in an underestimate of the overall

importance of the gopher tortoise to avifauna.

Density of gopher tortoise burrows is correlated

with increased mammal and reptile species

diversity (Catano and Stout 2015), but effects on

bird species diversity remain unknown. However,

1 University of Georgia’s Savannah River Ecology Lab,

P.O. Drawer E, Aiken, SC 29802, USA.2 Current address: University of Georgia’s Savannah

River Ecology Lab, P.O. Drawer E, Aiken, SC 29802,

USA.3 Corresponding author; e-mail: [email protected]

792

in other systems, greater bird species richness has

been attributed to the effects of ecosystem

engineers on the vegetation or insect communities

(e.g., Joseph et al. 2011). Bird density and species

richness are significantly greater in black-tailed

prairie dog colonies (Cynomys ludovicianus) than

in adjacent prairie in South Dakota (Agnew et al.

1986). The degu (Octodon degus), another small

mammalian ecosystem engineer, is associated with

increased invertebrate diversity, and granivorous

birds foraged more frequently and consumed more

in a shorter period than in areas with lower density

of surface runways created by O. degus (Root-

Bernstein et al. 2013).

As part of an unrelated study on gopher tortoise

reproduction and social behavior on two military

installations in the Florida panhandle, we moni-

tored burrows at each installation for 12 months

using remote wildlife cameras. We incidentally

recorded observations of birds visiting tortoise

burrows. We report overall bird species richness

detected at burrows at each site, calculate visitation

frequency of each bird species observed at

burrows, and report how birds were observed

using tortoise burrows and burrow aprons. Al-

though our monitoring efforts were not designed to

experimentally test hypotheses regarding differ-

ences in either gopher tortoise or bird activity

between sites, based on characteristics of the two

sites we can make some initial predictions. The

two installations, though separated by a short

distance, differed in several important ways that

might be expected to influence species diversity.

Naval Air Station (NAS) Whiting was larger in

size, but with less habitat diversity, lower propor-

tion of habitat suitable for gopher tortoises, and

greater intensity of military training compared to

Holley Outlying Field (OLF). Thus, we predicted

bird diversity and bird visitation at gopher tortoise

burrows to be greater at Holley OLF than at NAS

Whiting despite its smaller size.

METHODOLOGY

Study Sites.—We conducted our research at two

Department of Navy properties ~38.6 km apart in

Santa Rosa County in the Florida panhandle—

NAS Whiting and Holley OLF. NAS Whiting and

Holley OLF were both established in 1943.

Although they are in close proximity to each other

and fall under the same management complex,

they vary in military training intensity and

proportion of area suitable for gopher tortoises.

NAS Whiting is a 1,623-ha active airfield that

employs ~3,000 military and civilian personnel.

Combined, helicopters and small single-engine

airplanes engage in an average of 500 training

flights per day, 1.2 million training flights per year

(R. Cherry, pers. comm.). Substantial infrastruc-

ture exists on NAS Whiting, including buildings,

airstrips, and roads (405 ha, 25%). The remaining

1,218 ha is composed of open fields that occur

adjacent to runways (730 ha, 45% of total area)

and forested habitats (487 ha, 30% of total area),

which include a mixture of planted pine and

mature pine stands and patches of native scrub oak

habitat (Greene et al. 2008). Forested habitats are

managed through infrequent thinning, clear cut-

ting, and prescribed fire. However, stand quality

degrades rapidly without regular disturbance such

as fire or thinning, resulting in marginal habitat

conditions for gopher tortoises in most of the

forested habitats across the installation. Open

fields are mowed monthly during spring and

summer to maintain vegetation height require-

ments necessary for installation operations. These

open fields are the primary habitats on the

installation with the ground forage necessary to

support tortoises. Mowing is typically excluded

within small buffers around each marked tortoise

burrow (Smith et al. 2015), creating spatial

heterogeneity within the mowed fields. Although

234 tortoise burrows were detected at NAS

Whiting during a 2011 survey, only 58 tortoises

were documented (24.8% occupancy rate; Tuber-

ville and Grosse 2011). Because gopher tortoises

maintain more than one burrow, occupancy rates

are typically well below 100% and vary because of

a number of factors, including habitat quality

(McCoy and Mushinsky 1992). Gopher tortoises at

NAS Whiting occur in relatively isolated clusters

across the installation, with most active burrows

occupying airfields and rights-of-way or the

immediately adjacent forest (Fig. 1).

Holley OLF is a 283-ha decommissioned

auxiliary airfield with no active infrastructure

(Fig. 2). Although small planes may use the

airstrip for low approaches, it is not actively used

for ground training. Unused airstrips and roads

compose 28 ha (10%) of the total area. The

remaining 90% of the property consists of mature

pine stands (170 ha), open field (99 ha), and native

793White and Tuberville � AVIAN USE OF GOPHER TORTOISE BURROWS

scrub oak (14 ha; Greene et al. 2008). Addition-

ally, Holley OLF features two ephemeral wetlands

in the southeastern and southwestern edges of the

property. Mature pine stands are burned infre-

quently and open fields are mowed using a similar

regime as NAS Whiting. Tuberville and Grosse

(2011) recorded 109 burrows with an occupancy

rate of 19.2% (21 tortoises). Like NAS Whiting,

FIG. 1. Distribution of burrows of gopher tortoises on NAS Whiting in 2011 in Santa Rosa County, Florida. Top image

depicts occupied tortoise burrows detected during a survey in 2011 to illustrate the fragmented distribution of tortoises across

the installation. Inset (bottom) shows focal burrows monitored with wildlife cameras October 2013–September 2014 in the

South Field.

794 THE WILSON JOURNAL OF ORNITHOLOGY � Vol. 129, No. 4, December 2017

tortoise burrows are primarily in open field areas

surrounding the airstrip (Fig. 2), although the

native scrub oak habitat canopy remains open and

also supports some tortoises.

Burrow Monitoring.—We monitored active

gopher tortoise burrows at both NAS Whiting

and Holley OLF using remote wildlife cameras

(TrophyCam model 119736C, Bushnell Outdoor

Products, Overland Park, KS, USA) during

October 2013–September 2014. Cameras were

placed only at active burrows and relocated as

needed as tortoises shifted burrows. Active

FIG. 2. Distribution of occupied burrows of gopher tortoises (circles) detected in a survey in 2011 and focal burrows

monitored with wildlife cameras October 2013–September 2014 on Holley OLF military installation in Santa Rosa County,

Florida.


burrows are not always occupied but exhibit recent

signs of tortoise activity on the apron (the mound

of sand outside burrow entrance), such as tracks or

fresh sand from digging. We positioned cameras to

maximize the view of both the entrance and apron.

We programmed each camera to capture a burst of

three photos with 5-sec intervals between each

triggering event. We visited the installations every

4–6 weeks to check cameras and download photos.

At NAS Whiting, we maintained 7–10 cameras

among two clusters of burrows (~35 m apart) at the

southern edge of the South Field (Fig. 1 inset) for a

total of 3,329 camera days (i.e., sum of days each

camera was operational). At Holley OLF, we

operated 7–9 cameras at active burrows (Fig. 2) for

a total of 2,668 camera days. Total camera

numbers operational at each site at any given time

varied because of active burrow availability,

camera malfunction, and inclement weather con-

ditions (i.e., flooding of monitored burrows and

associated cameras).

Data Summary and Analysis.—We visually

inspected all photos captured on all cameras. For

each photo with a bird, we identified the

individual(s) to species when possible. Individuals

that could not be identified by us or by

ornithologists we consulted were excluded from

the analyses. For each individual, we recorded the

date, study site, burrow ID, and behavior of the

individual. Upon reviewing photos, we identified

three behaviors of birds that were repeatedly

detected by wildlife cameras at tortoise burrows

or aprons: foraging, wing-flashing, and dust

bathing. Foraging behaviors included observations

of birds with beak to the ground, scratching in the

sand, or with an insect or other prey item in its

beak. Wing-flashing is a type of displaying

behavior typical in mockingbirds although its

function is not well-understood (Hailman 1960,

Hayslette 2003). Wing-flashing is characterized by

both wings being opened upwards towards the

back in a series of quick, jerky movements, then

closed. Dust bathing, which birds perform for

feather maintenance, parasite control, and thermo-

regulation (Elphick et al. 2001), involved birds

clearly agitating the sand and flapping their wings.

All other behaviors, such as resting or sitting on

the apron, were classified as unknown.

We quantified the number of newly detected

bird species each month at gopher tortoise burrows

at each installation to develop species accumula-

tion curves for each site. To create the curves, we

pooled data from cameras at each installation to

calculate the cumulative number of species

detected across all monitored burrows. To compare

the frequency of burrow use or burrow visitation

among bird species (irrespective of site), we

recorded the number of days each species was

detected at any monitored burrow at either site

(max 1 visit per day, with data pooled across all

burrows at both sites). Data were pooled because

of the close proximity of cameras, vagility of birds,

and inability to distinguish individuals of same

species in photos. Thus, reported visitation rates

are conservative and underestimate total visitation

by birds.

To test for differences in total bird visitation

frequency between Holley OLF and NAS Whiting,

we used chi-square analysis to compare the

observed number of visits by birds that were

detected at burrows at each site to expected

frequencies that accounted for differences in

survey effort (i.e., camera days) between sites.

Additionally, we compared observed species

richness and number of unique species at each

site to expected values (also corrected for

differences in survey effort) using chi-square

analysis to test for differences between sites. All

analyses were performed in program R (R Core

Team 2008).

RESULTS

Monitoring duration varied among burrows

because of changes in tortoise activity or occu-

pancy status at monitored burrows. During the 12-

month study, we monitored a total of 15 burrows at

NAS Whiting for an average of 230 6 96 days

(mean 6 1 SD) per burrow. At Holley OLF, we

monitored 18 burrows for an average of 147 6 78

days per burrow. In total, we documented 599

visits by 33 species of birds representing 16

taxonomic families. We were unable to identify

birds to species for 26 visits, which were excluded

from further analysis. Twenty species (60.6%) had

not previously been reported in the literature as

associates of tortoise burrows. Species document-

ed included year-round residents (n ¼ 18), winter

residents (n ¼ 11), summer residents (n ¼ 2), and

migrants (n ¼ 2, species whose migration route


passes through the Florida Panhandle; Sibley

2000).

Although Holley OLF tended to have greater

bird diversity than did NAS Whiting in all metrics

we calculated, most comparisons were not statis-

tically significant. We documented 25 bird species

representing 14 families at Holley OLF and 19

species representing 10 families at NAS Whiting

(Table 1), but species richness was not significant-

ly different between the two sites (X2¼ 2.292, P¼0.13; Table 1). Eleven bird species (33%) were

documented at both Holley OLF and NAS

Whiting. More species were unique to Holley

OLF (14 species or 42%) than to NAS Whiting (8

species, 24%), but these differences were not

statistically significant (X2 ¼ 4.500, P ¼ 0.086).

However, we did observe significantly more visits

to tortoise burrows by birds at Holley OLF than

NAS Whiting (n ¼ 330, n ¼ 243 visits,

respectively), even after survey effort was ac-

counted for (X2 ¼ 39.748, P , 0.001). At Holley

OLF, species richness continued to increase

throughout the monitoring period. In contrast,

species richness at NAS Whiting plateaued

halfway through the monitoring period (Fig. 3),

suggesting additional monitoring was unlikely to

result in additional species detected at burrows of

gopher tortoises.

We calculated species-specific frequency of

burrow use as the number of days a species was

documented visiting any monitored tortoise bur-

row at either site (Fig. 4). Most species (n ¼ 25;

76%) were documented at burrows ,10 days

during the 12-month monitoring period. However,

some species were frequent visitors to tortoise

burrows, including Savannah Sparrows (Passer-

culus sandwichensis; 60 days), Northern Mock-

ingbirds (Mimus polyglottos; 41 days), Vesper

Sparrows (Pooecetes gramineus; 33 days), Wild

Turkeys (Meleagris gallopavo; 31 days), and

Eastern Bluebirds (Sialia sialis; 28 days). Seasonal

residents and migrants were on average more

frequent users of tortoise burrows or aprons than

year-round residents (mean¼ 12.6 6 20.9 days vs.

10.3 6 11.1 days, respectively). However, across

species, year-round residents were more consistent

visitors of the tortoise burrow or apron than

seasonal residents and migrants (standard devia-

tion ¼ 11.1 days vs. 20.9, respectively).

Most birds were observed using the burrow

apron rather than the tortoise burrow itself; none

were observed entering the burrow. Activity of

birds during most visits to burrow aprons could not

be categorized (493 of 573 visits). However, for

visits in which activity could be categorized (80

events), foraging was the most commonly ob-

served behavior (n ¼ 65 events). We documented

13 bird species foraging at tortoise burrows, 2

species dust-bathing (4 events), and only 1 species

displaying (11 events; Table 1).

DISCUSSION

Ours is the first study to report such high usage

of gopher tortoise burrows by birds. Based on the

number of visits detected and the diversity of

species observed visiting burrows, we suspect the

results of our study are not anomalous. Although

many species were recorded only once or twice

based on our conservative calculation of visits

(max of one visit per species per day), Savannah

Sparrows and the Palm Warblers were detected at

least 60 and 64 days respectively. Eastern

Bluebirds, Wild Turkeys, Northern Mockingbirds,

and Vesper Sparrows were also recorded .25

monitoring days. We observed only one bird

species that had previously been categorized as a

‘frequent’ visitor to gopher tortoise burrows—the

Northern Bobwhite (Colinus virginianus; Jackson

and Milstrey 1989).

Camera monitoring also revealed a variety of

uses of tortoise burrow aprons by birds. We

documented birds foraging, dust bathing, and

displaying. Mammal and reptile use of burrows

for overwintering habitat, foraging, and refuge has

been relatively well documented (Landers and

Speake 1980, Eisenberg 1983, Milstrey 1986,

Jackson and Milstrey 1989, Jones and Franz 1990,

Lips 1991). In this study, the most commonly

observed activity by birds was foraging on the

burrow apron, which had not previously been

reported in the literature. Species observed at

tortoise burrows in this study ranged widely in

their dietary preferences. Most species (n¼ 21) are

omnivorous, subsisting either primarily on inver-

tebrates or seeds but adjusting their diets season-

ally with availability of other forage options. Of

the remaining species with more specialized diets,

seven were insectivorous, two were granivorous,

and three were carnivorous (Rodewald 2015).

Tortoise burrows host an abundance of inverte-


TABLE 1. Bird species documented using remote-sensor wildlife cameras at burrows of gopher tortoises during October

2013–September 2014 at two Department of Navy installations (NAS Whiting and Holley OLF) in Santa Rosa County,

Florida. Residency classified based on species distribution or migrancy status in the Florida Panhandle in the given season

(Sibley 2000).

Common name Scientific name Holley OLF NAS Whiting Residencya Behaviorb

Gallinaceous birds

Northern Bobwhitec Colinus virginianus X YR F(4)

Wild Turkeyc Meleagris gallopavo X X YR F(6), DB(1)

Doves

Common Ground-Dovec Columbina passerina X YR

Mourning Dovec Zenaida macroura X YR F(1)

Plovers

Killdeer Charadrius vociferous X YR

Wading Birds

Cattle Egret Bubulcus ibis X YR

Raptors

Red-tailed Hawk Buteo jamaicensis X X YR

Great Horned Owl Bubo virginianus X YR

American Kestrel Falco sparverius X YR

Crows

American Crowc Corvus brachyrhynchos X X YR F(1)

Wrens

House Wren Troglodytes aedon X WR F(1)

Carolina Wrenc Thryothorus ludovicianus X YR F(1)

Thrushes

Eastern Bluebirdc Sialia sialis X X YR F(31)

Swainson’s Thrush Catharus ustulatus X M

American Robinc Turdus migratorius X X YR

Mockingbirds and Thrashers

Gray Catbirdc Dumetella carolinensis X WR

Brown Thrasherc Toxostoma rufum X X YR

Northern Mockingbird Mimus polyglottos X YR F(7), WF(11)

Warblers

Palm Warbler Setophaga palmarum X X WR F(6)

Pine Warblerc Setophaga pinus X YR F(2)

Yellow-rumped Warbler Setophaga coronata X WR

Prairie Warbler Setophaga discolor X M

Sparrows

Chipping Sparrow Spizella passerina X X SR

Field Sparrow Spizella pusilla X WR

Vesper Sparrow Pooecetes gramineus X X WR F(1), DB (3)

Savannah Sparrow Passerculus sandwichensis X X WR F(3)

Grasshopper Sparrow Ammodramus savannarum X WR

LeConte’s Sparrow Ammodramus leconteii X WR

Song Sparrow Melospiza melodia X WR

White-throated Sparrow Zonotrichia albicollis X WR

Cardinal and Buntings

Northern Cardinal Cardinalis cardinalis X X SR

Indigo Buntingc Passerina cyanea X YR

Blackbirds

Red-winged Blackbird Agelaius phoeniceus X YR

a Residency status classified as year-round resident (YR), a summer migrant (SR), a winter resident (WR), and migrant (M; Sibley 2000).b Behaviors classified were foraging (F), dustbathing (DB), and wing-flashing (WF). Number of detected events in photos given in parentheses.c Species previously documented at burrows of gopher tortoises (Jackson and Milstrey 1989 and references therein).


FIG. 3. Species accumulation curves for birds detected at burrows of gopher tortoises at NAS Whiting and Holley OLF

military installations, Santa Rosa County, Florida using remote wildlife cameras October 2013–September 2014.

0

10

20

30

40

50

60

70

detisiVsyaDforeb

muN

Bird Species

FIG. 4. Visitation frequency of bird species at burrows of gopher tortoises at NAS Whiting and Holley OLF military

installations in Santa Rosa County Florida. Frequencies represent the number of monitoring days during October 2013–

September 2014 that each species was documented at any burrow at either installation (max one visit per day).


brate species (Young and Goff 1939), some of

which may be attracted to the unique microclimate

offered by the burrow and its apron (Kaczor and

Hartnett 1990, Pike and Mitchell 2013) or to the

presence of tortoise feces as a nutrient resource

(Lips 1991). These insects can in turn attract

insectivorous birds. Likewise, the greater concen-

trations of seeds of legumes and fruits found in

tortoise feces that are often deposited in the burrow

vicinity (Jackson and Milstrey 1989, Boglioli et al.

2000) provide food resources for granivorous

birds. We suggest that given the diversity and

abundance of forage options at gopher tortoise

burrows, the sandy aprons (which can be up to 1

m2; Kaczor and Hartnett 1990) may serve as visual

cues for birds.

Other uses of gopher tortoise burrows by birds

reported in the literature or anecdotally include use

of burrows by Bachman’s Sparrows (Peucaea

aestivalis) as refuge from avian predators (Dean

and Vickery 2003). Additionally, Florida Scrub-

Jays (Aphelocoma coerulescens) have been ob-

served entering gopher tortoise burrows, presum-

ably as a refuge, after being experimentally

translocated from their home territory (R. Bow-

man, pers. comm.). Similarly, burrows of desert

tortoises (Gopherus agassizii) in the U.S. south-

west provide shelter from extreme heat for several

local bird species, including Horned Larks (Ere-

mophila alpestris) and Black-throated Sparrows

(Amphispiza bilineata; Walde et al. 2009, 2016).

Burrows of other fossorial species, including the

European rabbit (Oryctolagus cuniculus) and the

aardvark (Orycteropus afer), are frequently used

for shelter by both avian and non-avian fauna

(Galvez Bravo et al. 2009, Whittington-Jones et al.

2011). Our study adds to the growing body of

evidence that burrows of fossorial animals can

serve as an important resource for sympatric

species.

Although the species richness we observed at

NAS Whiting and Holley OLF represents only a

fraction of annual bird richness documented in the

county during the same monitoring period as this

study (33/253; eBird 2016), the diversity of birds

documented at tortoise burrows and the number of

visits detected was surprising. As expected,

burrow visitation frequency by birds was signifi-

cantly greater at Holley OLF than Whiting OLF

and may reflect overall patterns of bird diversity

between the two sites. Presumably, the lower

visitation frequency at Whiting OLF is because of

increased human activity and greater aircraft

training intensity, although our study was not

designed to test this hypothesis. However, the

sheer number of flights (average 500/day) and the

low altitude of aircraft near monitored gopher

tortoise burrows would have created chronic noise

disturbance. Although experimental studies are

limited, accumulating evidence indicates that noise

is an important determinant of habitat quality for

wildlife (particularly birds) and that birds may

avoid areas with high noise disturbance or alter

their behavior or activity patterns in response to

noise disturbance, including those caused by

military aircraft (Smit and Visser 1993, Pepper et

al. 2003, Barber et al. 2010).

We also detected greater bird species richness,

more bird families, and more unique bird species

at Holley OLF than NAS Whiting. While these

trends were not statistically significant, they may

be of biological relevance. Given the lower

monitoring effort at Holley OLF, its smaller size,

and that it is almost completely surrounded by

residential development (Fig. 2), it is remarkable

that we observed bird species richness that is at

least on par with that detected at the much larger

NAS Whiting. We suspect that the diversity of

habitat types in close proximity to each other, in

combination with low training intensity, collec-

tively contributed to the diversity of birds detected

at gopher tortoise burrows at Holley OLF. In

addition, the more urbanized surroundings of

Holley OLF may have concentrated species within

its boundaries by providing an oasis. Additionally,

avifauna at Holley OLF may have benefited from

its proximity to Eglin Air Force Base, which has

some of the largest tracts of intact longleaf pine

flatwood forest in the region and is only 2 km from

Holley but .10 km from NAS Whiting (Jacobson

and Marynowski 1997). Avifaunal richness in-

creases with proximity to protected areas (Loss et

al. 2009), and the proximity of Holley OLF to

Eglin AFB could contribute to the high level of

species richness. Previous studies have also noted

the value of DoD lands to conservation of avifauna

(Nott et al. 2003, Eberly and Keating 2006, Rivers

et al. 2010). Our findings help underscore the

importance of even small protected areas in

supporting local biodiversity (Crooks et al.

2004), especially in proximity to other protected

lands.


The value of military lands in sustaining

biodiversity, including rare and at-risk species, is

widely recognized (NatureServe 2004, Stein et al.

2008). In fact, DoD lands harbor more rare and at-

risk species than any other federal agency in the

United States (Stein et al. 2008), placing a

disproportionate burden of management for these

species on Department of Defense, which commits

more than $112 million to conservation and

management of these species a year (Khoury and

Leone 2015). Balancing the sometimes-conflicting

missions of maintaining military readiness and

conserving biodiversity is becoming increasingly

difficult as training demands on installations

increase at the same time land use changes outside

installations continue to erode regional biodiversi-

ty and ecological integrity (Lee Jenni et al. 2012).

In addition, other demands are being placed on

installations, including increased contribution to

energy conservation initiatives through on-site

production of renewable energy (Booth et al.

2010, Van Broekhoven et al. 2012). For example,

since concluding our monitoring project, a large

portion of Holley OLF where gopher tortoises

occurred has been designated for solar production,

resulting in displacement of resident tortoises and

potentially negatively impacting other species that

use their burrows. As a growing number of

military installations are repurposed (Burton and

Williams 2001), particularly those that have been

decommissioned or no longer contribute to

changing military training needs, we hope that

the potential contribution of these lands to the

biodiversity mission of DoD will continue to be

recognized. As DoD lands host some of the most

biodiverse habitats in the country, preserving them

when they are past their military use may be key to

continued preservation of the species that depend

on them (Havlick 2007, 2011).

Conclusions

Although our results represent just 1 year of

monitoring, they reveal a heretofore underappre-

ciated interaction between birds and gopher

tortoise burrows, the significance of which remains

unknown. Protection of gopher tortoises on

military installations may have positive effects on

bird conservation, aligning with the ecosystem or

community approach to conservation by the

military laid out by Boice (1999). Our findings

indicate that further non-invasive monitoring is

warranted to better understand the role of ecosys-

tem engineers on the vertebrate community,

especially in remnant natural areas and military

lands. We recommend that future controlled

studies be designed explicitly to quantify the

influence of gopher tortoises and their burrows on

local bird species richness and identify mecha-

nisms contributing to such patterns. Further, use of

video clips instead of photos, would be more

effective for understanding bird usage of tortoise

burrows and may clarify much of the ‘unknown’

behavior we observed in this study.

ACKNOWLEDGMENTS

Funding and support for this project was provided by the

Department of Navy (Agreement Number W9126G-13-2-

0027) and by Department of Energy under award DE-FC09-

07SR22506 to the University of Georgia Research Founda-

tion. We thank R. Cherry for project assistance with logistics

and installation access, R. Smith for regional-level support,

K. Buhlmann for field help and guidance setting up cameras,

and M. McPherson for field assistance. We also thank S.

Pruett, R. Cooper, and B. DeGregorio for donating their time

to help two herpetologists identify birds and to R. Chandler

for encouraging us to publish these findings. Finally, we

would like to thank R. Bowman and two anonymous

reviewers for their invaluable feedback and reviews of an

earlier version of this manuscript.

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