Egg size variation in birds with asynchronous hatching: is bigger really better?

Area of Science:

• Avian ecology
• Evolutionary biology
• Reproductive strategies

Background:

• Offspring survival in animals often correlates with birth size, but this is unclear in birds.
• Previous studies may be confounded by not accounting for asynchronous hatching (ASH).

Purpose of the Study:

• To investigate the effects of egg size and asynchronous hatching (ASH) on common grackle (Quiscalus quiscula) nestling growth and survival.
• To test if females adjust last-laid egg size to mitigate the negative impacts of ASH.

Main Methods:

• Assessed growth and survival of common grackle nestlings in relation to egg size and ASH.
• Conducted experiments with synchronized nests to isolate the effects of egg size and ASH.

Main Results:

• The impact of ASH on nestling growth and survival overshadowed the effect of egg size.
• Late-hatched nestlings experienced the highest mortality rates.
• Egg size influenced growth later in the nestling period only after starvation reduced ASH.
• In synchronized nests, both egg size and ASH affected early nestling growth.

Conclusions:

• Varying last-laid egg size is unlikely to provide an adaptive advantage for females in species with significant ASH.
• Future studies on maternal effects (e.g., egg size) should consider simultaneous maternal effects (e.g., ASH).