P0,1,2 = probability eggs survive given 0, 1, or 2 parentsW, w = eggs laid by deserting or caring female, respectivelyPM = probability deserting male mates again

Care

Abandon

F: wP2 WP1

M: wP2 WP1

F: wP1 WP0

M: wP1 (1+pM) WP0 (1+pM)

Care Abandon

FEMALE

MALE

If female cares then male should abandon if: wP2 < wP1(1+p)

Cost/benefit approach

Care

Abandon

F: wP2 WP1

M: wP2 WP1

F: wP1 WP0

M: wP1 (1+pM) WP0 (1+pM)

Care Abandon

FEMALE

MALE

- caring/abandonment by parents is a game between 2 players: M & F

- the best decision by one player depends on the decision of the other….

- we can understand caring/abandonmentin terms of the probability of remating (M), eggs laid (F) or loss of offspring when raised by a single parent (M and F)

- Environmental conditions that abruptly alter these costs and benefits may also abruptly alter parental care and mating strategy – e.g., facultative polygamy

Birds

Social Monogamy - 90% of all birds - primitive/original mating system - monogamy and biparental care go hand-in-hand (not w/o exceptions)

Why? What factors that promote monogamy and biparental care in birds?

Facultative Monogamy: individuals fail to acquire additional mates b/c of shortage of members of the opposite sex (e.g., synchronous breeding and unbalanced sex ratio)

Obligate Monogamy: Selection for monogamy per se – both sexes gain e.g., males are less successful with 2 mates than 1 e.g., in females, pairing with an unmated male better than with a mated male

Pair bonds may last for life (e.g., parrots, albatrosses, eagles, geese, pigeons), but separation is quite common, and usually after failed breeding attempts.

Lastly, if one considers passerines have 60-70% survivorship rates, there is a only a 36-49% chance both members survive til the next year – so why delay breeding waiting for a mate to show up – or not.

Mute Swans: 5% of breeding pairs and 10% of non-breeding pairs separate each year

In Adelie Penguins: 16% of old pairs and 44% of young pairs stay together more than 1 breeding season.

First and 2nd clutches of are 84% and72%, respectively, of the females body mass. Males contributes 42% of the food they gather to females before first clutch and care entirely for the young as 2nd is laid

What do males do?

Courtship feeding – Rifleman

Nest construction by males is the prevailing mode among non-passerines

E.g., Male Hairy Woodpeckers conduct 95% cavity construction (Lawrence 1967)

Are males necessary?

(1) Shared incubation - 67% of Families of Neognathous birds Western sandpipers – removal of either parent led to

100% failure

(2) Female provisioning – common in raptors, hornbills, and other groups

7 of 8 male kestrel removals resulted in nest abandonment (the exception wasa female who lost her mate on day 24 of a 27 day incubation period)

# Nests

# chicks fledged

Are males necessary?

(3) Post-hatching care - Effects of male-removal on nesting productivity…

Song sparrows – decrease by 51%Seaside sparrows – decrease by 66%Dark-eyed juncos – decrease by 38%

Also in kestrels, rock doves, tree swallows and other passerines.

(4) Post-fledging care – 3 passerine studies show loss of male leads to 37-66% reduction of young to independence

...conclude that in monogamy, both mates are necessary for raising young, and/or it is the strategy that yields the greatest # offspring for both male and females

Avian Reproduction

Finding/attracting Mates

Nest construction

Egg laying

incubation

Caring for young

Altricial young• Nestlings • Fledglings

Precocial young leave the nest after hatching

(1) Shared incubation

(2) Female provisioning

(2) Female provisioning (3) Post-hatching care

(4) Post-fledging care

EPCs – Extra-pair copulations – copulations outside the pair-bond

- Once thought to be very rare … until DNA-fingerprinting become common, now it appears everyone is doing it.

EPCs broods with extra- offspring fathered observed pair paternity by extra-pair matings

Black Vulture 0Common Loon 0Ea. Screech Owl 0Willow Warbler 0 0 0Fulmar 2 0 0 Wood Warbler 13 0 0Eu. Bee-eater 4 5 1Zebra Finch 5 8 2Pied Flycatcher -- 15 4Blue Tit 5 36 18Shag 14 20 18Red-winged Blackbird -- 47 28Purple Martin -- 54 35Indigo Bunting 2 48 35Superb fairy-wren 76

EPCs in the Red-winged blackbird

Benefits to EPCs

Males – sire more offspring so long as it doesn’t comprise the benefit from its socialmate

in value of paternal care

# opportunities (density of females)

in the ability to guard mate(from the female’s perspective of soliciting EPCs)

Benefits to EPCs

Males – sire more offspring so long as it doesn’t comprise the benefit from its socialmate

in value of paternal care

# opportunities (density of females)

in the ability to guard mate(from the female’s perspective of soliciting EPCs)

} Will the prevalence

of EPCs

Females – No gain in the # offspring, so why engage in EPCs?

(1) It is forced – Mallards (2) Insurance against infertile males(3) Sperm competition – may the best sperm win

or….

(4) Good Genes

Most females cannot mate with the best male (constraint) so they seek out EPCs to increase their overall fitness

Predicts: Females will seek EPCs with better males:

Test: Zebra finch (Houtman 1992)

0 +2 +4 +6-4 -2

Difference in rank between social mate and EPC-mate

ImprovementDown-grading

# males

Zebra finch

= EPCs

This begs the question of why not have more EPCs with the best/better males? …Probably risk of mate-abandonment if confidence of paternity is compromise

This begs the question of why not have more EPCs with the best/better males? …Probably risk of mate-abandonment if confidence of paternity is compromise

P0,1,2 = probability eggs survive given 0, 1, or 2 parentsW, w = eggs laid by deserting or caring female, respectivelyPM, pF = probability deserting mal/female mates again

Care

Desert

F: wP2 WP1 (1+pF)M: wP2 WP1

F: wP1 WP0 (1+pF)M: wP1 (1+pM) WP0 (1+pM)

Care Desert

FEMALE

MALE

If female cares then male should desert if: wP2 < wP1(1+pM)

Polygyny – polygymous mating system in which males have multiple mates - 2% of all birds

Paleognathous spp – multiple femaleslay in the male’s nest who then givesalmost exclusive paternal care

Neognathous spp –

New world – wrens and blackbirds (marsh-nesters)

Old world – Cavity nesters, e.g., some owls, pied flycatcher

Two models – (1) Polygyny threshold model (Orians 1969) (2) Deception model (von Haartman 1969) (3) no other choice – best of a bad situation

In Picman’s (1987) study of the marsh wren females settle with mated males only afterall bachelor males had paired

Polygyny threshold model posits that there is an uneven distribution of important resources that males control access to through territoriality

Thus, females must decide whether to (i) mate with an already mated male on a high quality territory or (ii) an unmated males on a poor territory.

The threshold is the point at which a female will do as good or better with option i

abcde

#1

1 ♀

2 ♀

FemaleReproductive

success

Territory Quality

abcde

#2

abcde abcde

#2#3?

abcde abcde

#2

abcde

#3

#5

#6

#4

Deception model posits that the female pays a cost of polygyny b/c the male conceals its bigamous relationship from the females

Male and femalePied Flycatchers

Once males attract one female they fly off to another nest site some distance away (200m, on average, but up to 3.5 km) to attract a second female. B/c of the distance, secondary females cannot assess whether they male as another mate

10-15% of males are successful at having 2 mates

Male Female #1Female #2

No male assistance

Some distance away

In conclusion, there are 3 scenarios that may lead to Polygyny:

(1) Females have no other choice but to mate with a mated male

(2) Females may be deceived

(3) Females may actively assess the consequences of their decision and make an adaptive choice

Care

Desert

F: wP2 WP1 (1+pF)M: wP2 WP1

F: wP1 WP0 (1+pF)M: wP1 (1+pM) WP0 (1+pM)

Care Desert

FEMALE

MALE

What if pF >> pM ?

Polyandry – polygynous mating system in which females have multiple mates

- 1% of all birds - involves sex role-reversal, such that females defend territories, compete for mates, take the lead in courtship

Occurs largely in shorebirds: - Painted snipes - Jacanas - Phalaropes - Plains wanderers

These birds often have abundant resources,require only a single parent to care for theirprecocial young, thus enabling the female to desert after laying eggs to find another mate.

♀ = 5.0

♂ = 5.0

♀ = 6.7

♂ = 3.7

♂β = 3.0

♀ = 3.8

♀β = 3.8

♂ = 7.6

DunnockPrunella modularis

Leks – Promiscuous mating system - 1% of birds - males provide no parental care - males congregate at sites not used for other purposes - no resources (territory) are on display for females - females chose among males a selected sperm donor

Cock-of-the-Rock: Classical Leks – conspicuously clumped

communal mating/display groundsoften with extreme fidelity from year to year

Manakins:Exploded Leks - solitary individuals

that may interact vocally

...also hummingbirds, scolopacids, birds-of-paradise, grouse, and a parrot

http://www.youtube.com/watch?v=T2Bsu4z9Y3k