Hatching Asynchrony in American Goldfinches: An Experimental Study.

Area of Science:

• Ornithology
• Behavioral Ecology
• Evolutionary Biology

Background:

• Lack's hypothesis suggests asynchronous hatching is an adaptation to food scarcity.
• Hatching asynchrony is common in many bird species, but its adaptive significance is debated.

Purpose of the Study:

• To test Lack's hypothesis on the adaptive value of asynchronous hatching in American Goldfinches (Carduelis tristis).
• To investigate the effects of seasonal and environmental factors on nestling development and hatching patterns.

Main Methods:

• Comparison of nestling growth and survival in natural asynchronous and artificial synchronous broods.
• Analysis of factors influencing hatching asynchrony, nestling growth, and survival rates.

Main Results:

• Asynchronous broods exhibited greater mass divergence and faster growth rate differences among nestlings.
• Brood reduction was more frequent in asynchronous broods; lightest nestlings grew slowest.
• Nestling survival and growth decreased with season and poor weather; hatching intervals increased seasonally.
• Heavy nestlings in asynchronous broods showed a slight growth advantage when food was limited.

Conclusions:

• Asynchronous hatching may offer a marginal benefit to older nestlings under food stress, but synchronous hatching promotes superior overall growth.
• Factors beyond nestling growth, such as parental constraints, likely influence the prevalence of hatching asynchrony in goldfinches.