Route flexibility is associated with headwind minimization in a long-distance migratory seabird

Area of Science:

• Ornithology
• Ecology
• Animal Behavior

Background:

• Seasonal migration is a widespread phenomenon across diverse taxa.
• Migratory routes can exhibit significant variability within individuals, even when destinations are fixed.
• Understanding the drivers of this individual-level route variation is key to comprehending migratory strategies.

Purpose of the Study:

• To investigate the variability of migration routes within individual common terns (Sterna hirundo) across different seasons and years.
• To identify factors influencing migratory route selection in common terns.
• To determine if environmental conditions, such as wind, play a role in shaping migratory pathways.

Main Methods:

• Analysis of geolocator tracks from 192 post-breeding and 149 pre-breeding migratory journeys of 84 common terns.
• Comparison of migratory routes across multiple years for individual birds.
• Correlation of migratory routes with environmental data, specifically prevailing winds.

Main Results:

• Little to no spatial consistency was found in migration routes within individuals across years, regardless of season or sex.
• Birds departing within similar time windows tended to follow comparable migratory routes.
• Pre-breeding migratory routes were associated with minimized headwind exposure, suggesting adaptive route selection.

Conclusions:

• Common terns exhibit flexible migratory route selection, adjusting their paths in response to environmental conditions.
• The observed route flexibility is likely an adaptive strategy for long-distance migratory seabirds.
• Migratory route choice appears to be influenced by immediate environmental factors rather than strict individual consistency.