Birds in two worlds: Carry-over effects of environmental and indivudual winter conditions on spring migration ecology

Habitat and climate changes cause worldwide the decline of migratory birds. However, most of studies on wintering conditions have not deepen the impact of anthropogenic land uses on migratory birds, neither the carry-over effects of environmental changes on birds’ physiology during spring migration. Key unexplored questions focus on how individuals respond to environmental variations in wintering sites and which are the carry-over effects on spring migration ecology. In this study, I first explore whether wintering environmental conditions drive the time and performance of spring migration. Then, I investigate how winter habitat quality and weather conditions en Mediterranean route influence birds’ physiology. Lastly, I study how the acute stress response of birds is affected by winter habitat quality and birds’ conditions at a stopover site. Once identified main wintering areas of several trans-Saharan species through stable isotope analysis in feathers and claws samples, I detect their winter ecological conditions by remote sensing earth data. An innovative, long-term and non-invasive metric of winter habitat quality employed is the corticosterone (CORT) concentration in feathers grown before spring migration. To instead reveal birds’ energetic conditions, plasma CORT, body fat and metabolite profiles are examined. CORT is associated with the energy demands of migration however, unpredictable environmental perturbations may alter its adrenocortical functions. To test this, I sample baseline and acute plasma CORT levels in birds arrived at the stopover. Overall, I hypothesise that 1) in trans-Saharan migrants, individuals more exposed to harsh environments in winter delay migration and arrive at the stopover with fewer energy stores, 2) individuals with higher feather CORT levels and/or birds that have encountered unfavourable weather during crossing exhibit bad physiological conditions, and consequently 3) a reduced response to a stressor. I examine if phenological and physiological dynamics of spring migration match with my predictions and discuss the ecological implications of my findings for spring migration ecology. Understanding the status of winter areas and its influence on migrants would improve the conservation efforts at the intercontinental scale.

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Konrad-Lorenz-Institut für Vergleichende Verhaltensforschung