5 - Mating systems: birds

Question 1

What is the dominant social mating system in birds?

Answer 1

Social Monogamy

• Both help raising of young
• Lots of extrapair mating

Question 2

Why aren’t female birds always roped into caring for offspring like mammals usually are?

Answer 2

They don’t lactate like mammals do

Question 3

What factors favour monogamy?

Answer 3

• If both parents needed for caring (remove one and the offspring die)
• The payoff for caring is greater than seeking more matings (eg. remove female and offspring die, no fitness, or remove male and female has reduced reproductive success)
• Female aggression (the settlement of a female on a first female’s property is most costly when they both have offspring at same time, therefore females attack most when they look like they’re settling at same time)

Question 4

What is the benefit to females for social monogamy (messing around)? (2 direct, 2 indirect)

Answer 4

Direct (non-genetic benefits)

• Increased resources from paternal care to extrapair mate
• Fertility insurance

Indirect (genetic benefits)

• Good genes
• Genetic diversity or complementarity

Question 5

What are two forms of polygyny?

Answer 5

• Female defense polygyny (males defend groups of females against other males)
• Lek polygyny (female pursuit of males, birds of paradise)

Question 6

What are the costs and benefits of resource defence polygyny for males and females?

Answer 6

Males
- Lots of breeding benefits

Females
- Sacrificing male care while he’s caring for/mating with other females

Question 7

What are two explanations to explain females benefits from male defence polygyny?

Answer 7

• No cost model, where polygyny is beneficial, especially for nest defence
• Polygyny is neutral, no big deal for many females to live together

Question 8

How would you get the evolution of polygyny even with costs to females?

Answer 8

Polygyny threshold model: the cost of sharing a territory is compensated by quality of territory

Question 9

What is the polygyny threshold model?

Answer 9

Territory quality predicts female reproductive success, which is higher for monogamous rather than polygynous mating

High quality territories more likely to have polygyny (similar to ideal free distribution)

Question 10

What is the deception cost to polygynous female birds?

Answer 10

• Male mates with a female then a second female. Takes care of first offspring but not second.

There’s probably a cost determining if a male has already mated or not. The cost of searching for a male might be greater than getting deceived

Question 11

How are the red-necked phalarope different from most other bird mating systems? How did this evolve?

Answer 11

They have polyandry where they compete for getting males, and defend a bunch of males from females.

Short breeding season in shorebirds. Males do incubation and caring for offspring. Females can then lay more eggs than a single male can care for, she must find several males.

Question 12

What are three cost models that explain the seemingly non-intuitive cost of polygyny for females?

Answer 12

• Polygyny threshold model
• Deception
• Cost of searching for a mate

Question 13

Describe three factors in polyandry

Answer 13

• Mainly male parental care of eggs
• Female’s ability to lay more eggs than a ale can care for
• Female competition to obtain several males to care for eggs