Temporal and spatial variation in reproductive benefits in a partial migrant

Area of Science:

• Ecology
• Evolutionary Biology
• Ornithology

Background:

• Partial migration systems involve both resident and migratory individuals within a single population.
• Residents are typically expected to have a reproductive advantage due to earlier breeding and better territories.
• Annual and spatial variations in environmental conditions may influence the relative reproductive success of residents and migrants.

Purpose of the Study:

• To investigate the temporal and spatial variation in reproductive output between resident and migratory red kites (Milvus milvus).
• To explore the influence of elevational gradients on the reproductive success of the two strategies.
• To understand how environmental variation impacts the coexistence of migratory and resident individuals.

Main Methods:

• Utilized 4 years of reproductive data from Swiss red kites.
• Collected 183 GPS-derived full annual cycle data from breeding individuals.
• Analyzed reproductive output in relation to elevation and temporal factors.

Main Results:

• Residents produced more fledglings than migrants at low elevations, but not at high elevations.
• Evidence of annual variation in the reproductive advantage of residents versus migrants was found.
• No significant difference in breeding initiation between residents and migrants, though later breeding reduced reproductive output.

Conclusions:

• Reproductive output differences between residents and migrants in partial migrant populations are influenced by distinct overwintering grounds and spatial breeding variables like elevation.
• Spatial and temporal variations in reproductive benefits are crucial for predicting migratory species' responses to environmental change.
• Elevational gradients significantly impact the relative reproductive success of resident and migratory red kites.