Migration is a predictable yet energy-intensive phase of birds’ life cycle, often involving crossing large ecological barriers with no opportunity to rest or refuel. The decision to embark on the journey strongly depends on environmental cues and the amount of energy reserves. Although birds can select favourable weather conditions at departure, weather variability during a barrier crossing may affect the use of energy reserves and the ability to cope with unpredictable events.
We investigated the effects of tailwinds and temperature encountered over the Mediterranean Sea during the pre-breeding migration on physiological conditions of two trans-Saharan migrants, the garden warbler (Sylvia borin) and whitethroat (Curruca communis), upon arrival to a stopover site, the island of Ponza. Our question was whether the ability to respond to a stressful event was influenced by the whether conditions experienced during the crossing.
We found that birds were not significantly affected by weather variability during the sea crossing if they had sufficient energy reserves. Both species were able to mount a full acute stress response as measured by the release of the hormone corticosterone. In the garden warbler, higher temperatures actually facilitate the response. These findings offer novel insights into corticosterone dynamics and physiological flexibility during spring migration. The paper has been published in Journal of Avian Biology and is freely accessible here.
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