Climate change and micro-geographic variation in laying date

Area of Science:

• Ecology
• Climate Change Biology
• Ornithology

Background:

• Climate change is altering species' reproductive timing, often advancing it with rising temperatures.
• Differential reproductive timing among sites can lead to disproportionate contributions to local recruitment.
• Understanding micro-geographic variation in breeding phenology is crucial for predicting population dynamics.

Purpose of the Study:

• To investigate micro-geographic patterns in barn swallow (Hirundo rustica) breeding timing.
• To determine if early-breeding sites contribute disproportionately to reproductive success.
• To identify characteristics of early-breeding sites and their occupants.

Main Methods:

• Analyzed spatial variation in barn swallow laying dates across 39 sites (1971-2004).
• Assessed plant phenology (elm leafing, snowdrop flowering) at early-breeding sites.
• Compared reproductive success, breeder density, and adult traits between early and late sites.

Main Results:

• Individuals at early-breeding sites had disproportionately higher reproductive success.
• Early sites exhibited earlier plant phenology and greater advancement in laying dates.
• Early sites hosted more breeders over more years and produced more fledglings.

Conclusions:

• Phenologically early sites are critical for barn swallow recruitment, producing disproportionately large numbers of offspring.
• Temporal changes in reproduction timing are linked to differential recruitment at early-season sites.
• Differences in adult body size and secondary sexual characters were noted at early sites.