Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Evaporative cooling and stopover strategies of migratory songbirds during desert crossing.

Auteur : Paces, Bernhard

Université de soutenance : Universität Wien

Grade : Master of Science (MSc) 2019

Résumé
European-African long-distance migratory birds cross the Sahara Desert twice a year. Generally, they fly during the night and stop over during the day. Once landed, they have to decide whether to refuel or to rest. In general, xerophilic bird species breeding and / or overwintering in arid habitats cross the desert with rather low fat stores and actively forage during stopover, while mesophilic species often carry enough fat reserves to cross the desert without refuelling en route. However, the underlying physiological adaptations causing this difference remain unclear. In this study, I measured cutaneous water loss (CWL) and temperature of panting onset of three closely related trans-Saharan migratory songbird species to test the hypothesis that species which actively refuel in the desert have a lower surface-specific CWL and a higher temperature of panting onset. These adaptations would allow them to sustain higher levels of activity in a desert environment and to extend the daily time window for foraging while keeping a low risk of dehydration. As expected, the mesophilic Blackcaps had a significantly higher surface-specific CWL and a lower temperature of panting onset than the xerophilic Lesser Whitethroats and Willow Warblers. This result corresponds to prior studies which showed that Willow Warblers actively refuel en route and carry relatively low fuel loads despite being a mesophilic species. This study demonstrated for the first time that surface-specific CWL and the temperature of panting onset coincide with the observed refuelling strategies in three trans-Saharan migratory songbird species. Thus, physiological constraints for maintaining a healthy water balance may be of major importance in the evolution of species-specific refuelling strategies in extremely arid climate conditions. This knowledge will provide valuable insights into the species’ response to climate change and contribute to the urgent need for research about distribution patterns, habitat use and feeding ecology of declining trans-Saharan migratory bird species at their staging sites.

Mots clés : ater balance / cutaneous water loss / temperature of panting onset / refuelling strategies / arid habitat adaptations / Sahara / warblers

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