Breeding in Birds

This set of flashcards covers key vocabulary and concepts related to bird breeding and reproductive strategies.

Clutch Size

The number of eggs laid in a single nesting attempt by birds.

Food Limitation Hypothesis

The hypothesis that clutch size is adjusted by natural selection to the maximum number of nestlings the parents can feed.

What evidence supports the Food Limitation Hypothesis?

Experimental manipulations where clutch sizes are altered (e.g., adding or removing nestlings) often show that parents struggle to provide adequate food for larger broods, leading to reduced nestling survival, growth, or future parental reproductive success. This suggests that clutch size is typically adjusted to the maximum number of offspring parents can feed.

Trade-off Hypothesis

The hypothesis suggesting that current reproductive effort is influenced by long-term reproductive interests, balancing between clutch size and adult survival.

What evidence supports the Trade-off Hypothesis?

Studies show that increasing current reproductive effort (e.g., by experimentally enlarging clutches) often results in a decrease in the adult's future survival or subsequent reproductive output. This demonstrates a trade-off where investments in current offspring negatively impact the parent's long-term reproductive interests.

Longevity

The length of time for which an organism lives; in birds, longer life spans often correlate with lower reproductive investment.

Interspecific Variation

Differences in traits, such as egg size or clutch size, observed between different species.

Intraspecific Variation

Differences in traits, suchs as egg size or clutch size, that occur within the same species.

Survival Rates

The percentage of individuals surviving in a given environment; larger bird species tend to have higher survival rates than smaller ones.

Parental Investment

The time and resources that parents contribute to the upbringing of their offspring, impacting their survival.

Latitudinal Gradient

The pattern where clutch size in birds generally increases with increasing latitude (e.g., larger clutches in temperate and arctic regions compared to tropical zones). This variation is theorized to be caused by environmental factors such as:

1. Increased productivity: Longer daylight hours at higher latitudes allow more foraging time during breeding season.

2. Seasonality: A pronounced breeding season in temperate zones with abundant, ephemeral food resources.

3. Predation: Possibly lower nest predation pressure in some higher latitude environments compared to tropical regions, or different predation strategies.

Phenotype

The observable physical or biochemical characteristics of an organism, as determined by both genetic makeup and environmental influences.

What are the key adaptive characteristics of bird eggs?

1. Shell Strength and Porosity: Shells are strong enough to protect the developing embryo and withstand parental weight during incubation, yet porous enough to allow vital gas exchange ( ext{O}2 in, ext{CO}2 out).

2. Shape: Varies from spherical to highly pointed. Pointed eggs (e.g., murres) are adapted to prevent rolling off cliff ledges; oval shapes facilitate efficient packing in the nest.

3. Coloration and Patterning: Provides camouflage against predators, especially for open-nesting birds, or can aid in parental recognition of their own eggs in colonial species.

What are the main drivers of interspecific variation in bird egg size?

1. Body Size of Parent: Larger bird species typically lay larger eggs, although egg size relative to body size can vary.

2. Clutch Size: Species laying larger clutches often produce relatively smaller eggs, reflecting a trade-off in resource allocation.

3. Developmental Mode: Precocial species (young are relatively independent at hatching) lay larger eggs with more yolk to support advanced embryonic development, compared to altricial species (young are altricial and helpless at hatching).

4. Life History Strategy: Species with higher adult survival and lower annual reproductive rates may invest more energy per egg over fewer breeding attempts.