Bird Biology Part 1

Stages of the avian nesting cycle

1) prenest

2) build nest/lay eggs

3) incubate

4) nestlings

Purpose of reproduction

genetic contributions to future generations

How do you define a male and female birds?

anisogamy - different sized gametes

Avian reproduction - males

• Smaller gametes = SPERM
• Produce billions
• Small investment
• Males can increase the number of offspring they produce by mating with more females

Avian reproduction - females

• Larger gametes = EGGS
• Fewer in number
• Contain lots of stored energy, each egg is a large investment
• Females are limited in terms of number of offspring by the amount of energy it takes to produce them

Social Monogamy

individuals pair off with one member of the opposite sex for one to several breeding periods

80% - 90% of birds, share parental care

Mate-guarding monogamy

males associate with a female to prevent her from mating with other males

Mate-assistance monogamy

males associate with a female to help her increase the number of offspring reared per breeding season

Female-enforced monogamy

males associate with a female that is capable of preventing her partner from seeking other males

Polyandry

females accept sperm from more than one male per breeding season

• males are more choosy

• females must develop sexually-selected traits

• 25% larger than males

<1% of all birds, male parental care

ex: Red-necked Phalarope

Male-enforced polyandry

females are forced to copulate with sexually aggressive partners

Convenience polyandry

females mate with more than one male because the costs of rejecting secondary suitors is too high

Material benefits polyandry

females mate with more than one male to secure the resources or the parental care that secondary partners provide

Fertility insurance polyandry

females mate with more than one male to reduce the probability that a primary partner’s sperm are defective

Genetic benefits polyandry

females mate with more than one male to secure purely genetic benefits from their partners, such as more compatible gene combinations for their offspring or greater heterozygosity for their progeny

Polygyny

some males are able to gain sexual access to two or more females

~2% of birds, parental care by females

Deception-based polygyny

males induce secondary females to pair with them be behaving as if they were monogamous

Female-defense polygyny

males defend and monopolize groups of potential mates against rival males

• females will cluster for protection and males exploit

ex: Montezuma Oropendolas

Resource-defense polygyny

males defend and monopolize valuable resources that attract several mates to them

• polygyny should be better for males based on gamete size but only if they can monopolize resources

• Patchy availability of territories - Might pay (reproductive success) for the female to be the second female on a good territory vs. first female on a poor territory

ex: Red-winged black bird

Lek polygyny

males defend a small display territory where they must persuade visiting females to ONLY mate with them

ex: Greater Sage grouse

Males with low investment sperm should chose?

Quantity

Females with high investment eggs should choose?

Quality

Social mate

the individual with which a bird has a pair bond

Extra-pair copulation

matings between two members of a population who are not pair bonded, usually when each is socially pair bonded to a different mate

Extra-pair fertilization

the fertilization of eggs resulting from matings between two members of a population who are not pair bonded

Cryptic female choice

• often difficult for female to refuse male

  • dangerous, ducks

• Easier for females to copulate with many males but be choosy with sperm

  • chicken females can eject low quality sperm

Reproductive retaliation

a behavior in which one member of a pir provides less parental care in situations where the offspring in the nest may not be their own and or when their mate also provides less care

Why monogamy in birds?

• reproductive realiation

  • incentive for female not to copulate with other males as males may reduce parental care

  • if male abandons the female to secure another partner, she may copulate with another male

• Mate-guarding

  • Seychelle’s Warbler

• Mate-assistance hypothesis

mate guarding

a behavior in which a male attends closely to his mate during her fertile period to help ensure she does not mate with other males

mate-guarding hypothesis

guard her while she’s fertile and seek EPC’s after she’s laid her egg

Mate-assistance hypothesis

• once egg is laid, both parent birds can assist with all remaining stages of chick development (bi-parental care)

• due to altricial development

• need both parents to assist with feeding them

• important during incubation

Promiscuity

males defend a clumped resource that attracts females

• common in tropical nectivores and frugivores

ex: lekking

Polyandry Problem - How do they know they sired the kids?

• 10% cuckoldry due to stored sperm

• primary males have higher paternity assurance

• secondary males may get more help

ex: Spotted sandpiper

Polygynandrous - Dunnock

• Variation in resource availability and relative competitive abilities

• Females always defend exclusive territories; whereas males do not

• Males sharing a territory are not related and have a strict dominance hierarchy

• Size of female territories reflects resource availability and competitive abilities