Lecture 17 Ornithology Mates and Mating Systems

What is monogamy?

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

What is the most popular form of mating system among birds?

Social monogamy, have on lasting pair bond but engage in EPCs (=extra pair copulations)

Why is social monogamy favored?

Balances the favorability of promiscuity, eggs are costly and sperm is cheap, and the benefit of parental involvement ensuring more young survive.

What are the various ways that males are involved in raising young?

1. males feed brooding females and/or feed young. ex: most songbirds

2. males share incubation duties. ex: herons, egrets, some woodpeckers, many songbirds

3. males place themselves in danger to defend nest and young from predators, ex: geese, swans, gulls, terns

What is an example of a bird that forms a life long pair bond?

swans, oystercatchers

What is an example of a bird that pairs for successive seasons?

American Robin

What is the general purpose of courtship displays?

female assessment of male prospective commitment and ability in raising young

What factors do courtship displays indicate to females?

1. health (ex: house finch plumage)

2. ability to provide food (ex: Northern Cardinal presents food items)

3. ability to provide shelter (Western bluebird presentation of nest or nesting material)

4. ability to defend territory (Cedar Waxwing aggressive display to show a males ability to defend his territory)

What is the purpose of mutual display?

In long term pair bonds, mutual display is needed for mutual assessment of partner:

1. reaffirms pair bond

2. stimulates courtship

3. coordinates breeding behavior

Example of mutual display behavior

Wandering Albatross mutual display by spreading wings and “dancing”

What are the benefits of EPCs for females?

1. fertility insurance against males infertility

2. genetically diverse young

3. improved genetic quality of young if they have a dominant extra pair mate

4. increased access to resources

What are the benefits of EPCs for males?

1. increased fitness

2. possible future mate acquisition

3. insurance against mate’s infertility

What is polygyny?

when 1 male pairs with 2 or more females, common among marsh and grassland songbirds

What is resource defense polygyny?

males control access to females through monopolization of critical resources.

What conditions favor polygyny as a mating style?

variation in territory quality, the environmental potential for polygyny increases with clumped resource distributions

What is an example of resource defense polygyny?

Marsh wren males build multiple nests on their territory, more nests means they have more mates

What is promiscuity?

engagement in indiscriminate sexual relationships, usually brief in duration ,no pair bonds

What is Lek promiscuity?

Males compete for status in communal display and females choose among them. There is great variation in mating success meaning usually only one male mates.

What is a regular lek vs an exploded lek?

The more common lek is a small display ground near other males that a male defends (ex: sage grouse)

An exploded lek is a scattered display ground (ex: bower birds, manakins)

Example of Lek promiscuity

ruff males different statuses: darker ones are dominant and lighter ones are subordinate. Darker males defend leks where they display and mate, lighter ones look more like females and recruit females on to dark’s territory. In the short terms the darker ones have more reproductive success, but the light colored ones have longer life spans so their overall reproductive success is equal.

Display is ruffling elaborate feathers, jumping, fighting

Initial conditions for evolution of Leks

1. resources are abundant enough that females can raise young on their own

2. males may be too conspicuous to offer parental assistance

3. gathering males for display reduces predation risk, they have safety in numbers

4. a) hotshots hypothesis

   b) hotspots hypothesis

What is the hotshots hypothesis for evolution of lek promiscuity?

The hotshots hypothesis states that males will cluster because subordinate males gather around attractive males to have a higher chance to interact with females drawn to hotshots

What is the hotspots hypothesis of lek promiscuity?

The hotspots hypothesis states that males gather at sites where females are abundant or more likely to congregate

What is polyandry?

One female mates with many males

males incubate and care for young, females compete for mates

What is simultaneous polyandry? Example

each females holds large territory containing smaller nesting territories with two or more males

ex: Northern Jacana

What is sequential polyandry? Example

female mates with a male, lays eggs, then terminates the relationship with that male, leaves him to incubate the eggs while she mates and repeats with another male

ex: spotted sandpiper

What factor leads to the development of polyandry?

Fixed egg clutch size, makes it so that the only way a female can increase her reproductive success is to lay more clutches. There is very fixed clutch size in shorebirds.

What is polygynandry? Example

multiple males pair with multiple females, there are still pair bonds

ex: acorn woodpeckers

What is cooperative breeding? Example

Helpers provide care for young that aren’t theirs, care given usually includes food, territorial defense, nest construction, incubation, and/or defense from predators.

ex: Florida Scrub Jay

Ecological constraints that lead to cooperative breeding

1. few vacant territories of good quality habitat

2. few suitable breeding partners available

3. little chance of successful reproduction until they can gain parenting experience

What are the benefits of cooperative breeding (aka philopatry)

1. survival via group membership

2. chance to increase survival of close relatives

3. chance to acquire superior territory either by monitoring vacancies in neighboring sites or by inheriting them