Increase in protandry over time in a long-distance migratory bird

Area of Science:

• Ecology
• Evolutionary Biology
• Ornithology

Background:

• Protandry, where males arrive first for reproduction, is crucial for migratory birds' fitness and response to climate change.
• Existing studies lack detailed analysis of protandry dynamics using breeding site data.

Purpose of the Study:

• To investigate the 38-year dynamics of protandry in willow warblers (Phylloscopus trochilus).
• To analyze changes in arrival timing for males and females and its impact on protandry.

Main Methods:

• Analysis of arrival records from two periods: 1979-1988 and 2006-2016.
• Investigation of protandry at both population and within-pair levels.
• Correlation of arrival timing shifts with temperature changes.

Main Results:

• Both male and female willow warblers advanced their arrival times, with males showing a greater advancement.
• Protandry increased significantly at population and within-pair levels.
• No change in sex ratio was observed; increased protandry correlated with temperature changes.

Conclusions:

• Warmer springs may be relaxing natural selection against early male arrival, driving increased protandry.
• Climate change appears to induce sex-specific phenological shifts in migratory birds.
• Differential timing of life-history events in response to environmental change warrants further evolutionary investigation.