Migration is an energy-intensive phase of birds’ life cycle, often including the cross-ing of large ecological barriers during non-stop flights. Corticosterone (CORT), anadrenocortical hormone also known as the stress hormone, generally rises at the onsetof migration to facilitate and sustain high-energy metabolism. Although birds canselect favourable meteorological conditions at departure, weather variability en routemay affect the migrants' energy reserves and their ability to cope with other stressors.This study investigated the effects of weather conditions on the physiological statusof two nocturnal trans-Saharan species, the common whitethroat Curruca communisand the garden warbler Sylvia borin, upon arrival at a stopover island after crossing theMediterranean Sea during pre-breeding migration. We assessed fuel stores and CORTvariations in relation to tailwinds and air temperature experienced over the sea route.Birds that arrived at the stopover site with residual energy reserves after encounteringmoderate headwinds or lower temperatures had similar baseline CORT concentrationscompared to those that migrated with tailwinds and higher temperatures. While bothspecies exhibited a normal stress response to catching and handling, stress-inducedCORT levels were correlated with higher temperature only in garden warblers. Ourstudy provides novel insights into CORT dynamics, suggesting that nocturnal migra-tory Passerines are not largely affected by weather variability across a marine barrierduring pre-breeding migration if they have sufficient energy reserves.
Massimiliano Cardinale (Wed,) studied this question.