Nests and Mates 29 June 2010

1.) Protection from predators 2.) Provision of a microclimate

suitable for egg incubation 3.) Cradles for dependent young 4.) Roosting chambers for adults

attending their eggs and young

Nests have four primary purposes

Other animals build nests, but birds do so in a greater variety of forms, from a greater variety of materials, and on a greater variety of sites

Nests may include a variety of material including green vegetation (e.g. Yarrow, Red-cedar) which may inhibit the growth of bacteria and reduce parasite loads

Evolutionary History

Satin Bowerbird

Nest safety

Invisibility, inaccessibility, and impregnability all contribute to nest safety

Many birds nest in trees, because ground nests are more likely to be predated

Enclosed (pensile) nests may deter predators, as may cavity nests

Distraction displays may also be used

Horned Coot photo from http://es.treknature.com/gallery/South_America/Chile/photo219194.htm

Pros◦ Less likely to be predated (safety in numbers,

mobbing, etc.)◦ Synchronized nesting provides a sudden abundance

of chicks◦ Can follow neighbors to good food sources

Cons◦ Increased competition (nest sites,

materials, even mates)◦ Large groups may attract predators◦ Parasites and diseases can easily

be spread

Colonial Nesting

1.) Shortage of safe nesting sites

2.) Abundant/unpredictable food source distant from available nest sites

Peach-faced Lovebirds (Agapornis roseicollis) tuck nesting material into feathers by rump

Yellow-collared Lovebirds (Agapornis personatus) carries nesting material in its bill

Hybrids attempt to tuck material into body feathers but typically fail

Village Weaver

Birds imprint on natal sites

Birds become more experienced at building nests with time

Development of the embryo is best at temperatures between 37-38 C

Ducks typically line nests with down to help insulate the eggs

Placement in or out of the sun, shade or wind has a major effect on the nest microclimate

Nest Microclimates

A Monk Parakeet nest in Borehamwood, UK (north side of London)

Most female birds lose feathers to form an incubation patch (or brood patch)

Seasonal development of patches is under hormonal control◦ Prolactin & estrogen stimulate

defeathering and vascularization

◦ Progesterone stimulates thickening and increased sensitivity of the epidermis

Brood Patches

Image from: http://www.hiltonpond.org/ThisWeek040415.html

Effects of inadequate incubation behavior

European Starling

Crested Myna

Malleefowl

Image from: http://www.sustainability.dpc.wa.gov.au/CaseStudies/OilMallee/malleefowl/Malleefowlprint.htm

Out of nest

In nest

Mates will often feed the incubating bird

Reproductive success of males is limited by mates Female reproductive success is limited by the production of

eggs Recent research on mating systems views monogamy as a

temporary truce between selfish, competitive individuals

Monogamy◦ The predominant mating system in which there is

a prolonged and essentially exclusive pair bond with a single member of the opposite sex for purposes of raising young

Polygamy◦ Any mating system involving pair bonds with

multiple mates of the opposite sex

Mating Systems

Polygyny◦A type of polygamy in which a male pairs with more than one female

◦If the male pairs with two females it is bigamy

Polyandry◦A type of polygamy in which the female pairs with multiple males.

Mating Systems Continued

Polygynandry◦A type of polygamy in which a female pairs with several males, each of which pairs with multiple females

◦Common in ostriches, rheas, emusPromiscuity

◦Indiscriminant sexual relationships, usually of brief duration

Mating Systems Continued

Birds are generally monogamous, although separations do occur◦ E.g. roughly 5% of breeding pairs of Mute Swans

separate each year Males and females evaluate quality of mates

◦ Females judge males by plumage, displays, courtship feeding etc.

◦ Males must evaluate female receptiveness, probability that offspring carry their genes, sperm competition, etc.

MonogomyExtra-pair copulation can be surprisingly frequent!

Extra-Pair Copulations Monogamy doesn’t

necessarily mean faithfulness!

Interestingly, in humans ~30-40% of dating relationships and 18-20% of marriages are marked by infidelity

~3.7% of human children are thought to be the result of infideltiy (Bellis et al. 2005)

Older, more experience males claim the top level(s) of a purple martin house

They sing a “dawn song” to attract other purple martins to nest colonially

The older martins then mate with the females of the less experienced males!◦ Yearling males father only 1.3 fertilized eggs

out of a clutch of 4.5 eggs◦ The older males father 4.5 fertilized eggs

with their mates, plus another 3.6 fertilized eggs with the mates of the less-experienced males!

Purple Martin EPC

Species living in stable environments with uniform food distribution tend to be territorial and monogamous

Species living in areas that occasionally have superabundant food (e.g. fruits) tend to polygynous

Care of young also has an influence◦ Birds that produce nidifugous

(precocial) young are more likely to be polygynous

Mating Systems & Ecology

Resource-defense Polygyny

Polyandry

Polyandry may arise due to female desertion

Many promiscuous birds display in a communal lek

Why lek?◦ “Hot spots” (male-

initiated model) vs. “hot shots” female initiated model)

Leks

Much of the field research on birds involves finding nests.

Researchers search for and monitor nests to look at:◦ Reproductive success under various habitat

management schemes◦ Reproductive success of individual species◦ Fledging success in areas with numerous cowbirds

and areas without ◦ Etc.

Field Methods: Finding Nests

BBIRD Protocol

At each site, you’ll want to find at least 20 nests per treatment/habitat per year for each of the common local species◦ When I did this, we would typically aim for finding

100+ nests each summer◦ Nest plots should be at least 4 ha in size,

preferably bigger so you can nest point counts or point transects in them In eastern deciduous forest, for example, it’s

recommended that you use eight 35-50 ha plots◦ Plots should be randomly chosen

Establishing Nest Search Plots

Plots should be searched for nests every 2 days

When you find a nest, make sure you can find it again! ◦ Record distance and orientation from a known

point and write a written description so others can find it as well.

◦ BBIRD has standardized field cards on website you can fill out

Finding new nests

1.) Parent behavior◦ saw a parent bird and followed it to the nest or area

around the nest. If the parent gets you within approximately 50 cm of the nest then parental behavior is considered the only cue used

2.) Parent flushed from nest◦ you flush a bird off its nest while walking past. This differs

from luck because behavior of the bird is important to location of the nest.

3.) Systematic search◦ nests found during a systematic search of possible nest

sites. This may occur without previous observations of other cues, or after parental behavior or non-behavioral cues suggest a nest is present nearby.

Cues for nest finding

4.) Non-behavioral cue◦ a non-behavioral cue suggests a nest is nearby. The nest is

then located by systematic searching or waiting for parents. Example: you notice fresh wood chips on the ground near a group of trees. You then locate the nest by searching nearby snags.

5.) Luck◦ came across a nest by chance without actively searching for it

or seeing parental cues. 6.) Previous year

◦ found nest based on knowledge of nest location from previous year.

7.) Young behavior◦ young's behavior led observer to nest. For example, noisy or

begging young often can lead you to find nests of cavity nesting birds.

Cues for nest finding continued

Active nests should be checked every 3-4 days, ideally every other day

Check nests from a distance (and avoid disturbing parents) if possible

Nest-building birds or birds just starting to lay eggs are more likely to abandon the nest

Avoid creating paths to nests (predators may follow them) and never check nests if predators are nearby

Monitoring nests

Building nest Incubating Nestling

Ruby-throated Hummingbird

6 – 10 days 12 – 14 days 18 – 22 days

Field Sparrow 2 – 8 days (depending upon time of year)

11-12 days 7-8 days

Northern Cardinal

3 – 9 days 11 – 13 days 9 – 10 days

American Crow 10 – 14 days 16 – 19 days 33 – 43 days

Time spent Incubation & caring for nestlings vary

There are two parts to this 1.) Information about the nest substrate

◦ Record information about nest height, dbh of tree, plant species, nest orientation, % overhead cover, etc.

2.) Information about surrounding vegetation ◦ Establish a 5 m radius plot (centered on the nest)

and an 11.3 m radius plot (also centered on the nest) The 5 m plot is used to count shrub & sapling stems &

measure ground cover The 11.3 m plot is used to count the number of trees

Gathering information on vegetation

Should be done every three years to track changes in vegetative community

Systematic Vegetation Sampling in Study area

Image from http://www.umt.edu/bbird/protocol/veg.htm

BBIRD protocol suggests that fixed-radius point counts (where you count all birds within 50 m in a 10 minute period) should be carried out three times per year.

Distance estimation techniques (i.e. transects or point transects) are now more widely used to examine bird density.

Point Counts