Minimizing dehydration risk in migratory birds in the desert

Several species of European migratory landbirds cross the Sahara Desert twice a year to move between their non-breeding to their breeding areas. While desert inhabitants have evolved physiological and behavioural strategies to survive the harsh environment, these migrants do not possess specific adaptations, since they only spend a short part of their life in this environment. However, especially during spring migration, large numbers can be found stopping in desert oases. In the past, we observed that some species were usually stopping just for a short time, mostly one day, resting in the shade and continuing their flights on the following night. There are species, however, that can stop at such sites for several days and forage actively, even in very hot and dry conditions. In this project we aim at understanding this difference, which we believe may be linked to the physiological propensity of different species to balance the use of evaporative cooling for maintaining their body temperature with the risk of dehydration. We will therefore (1) measure activity levels of different species with the highest level of precision, using automated radiotelemetry which will enable us to track the behaviour of the birds throughout their stay, and (2) in the same species, we will measure physiological parameters related to their ability to save water while maintaining their body temperature at healthy levels. To do that, we will measure water loss and the temperature of panting onset in a respirometry setup. The study will be conducted at a spring stopover site in South- Eastern Morocco, and we will measure six closely related species of about the same body size. We already know that these species are using different stopover strategies, from long stopovers and active foraging to short and inactive stopovers. We expect to find a link between activity and the rates of evaporative water loss and temperatures of panting onset, i.e. in the ability to spare water. We will then investigate the flexibility of the species to react to local conditions. Some desert oases can offer freshwater, though this availability may not be predictable. Theoretically, we would expect that when water is available the constraints posed by the risk of dehydration would be relaxed. This may offer opportunities to afford higher rates of water loss, given the chance of replenishing the loss easily. In a field experiment, we will alternate periods of water availability to dry periods and will again track the birds behaviour using automated radiotelemetry. We expect to see more activity, especially in species that are usually inactive. This would show that the birds can respond quickly to favourable conditions whenever they find them. To understand whether the ongoing desertification will affect migratory species, we need to understand how they respond to aridity. This project will inform conservation and enable to predict which species may become more sensitive to climate change.