Body condition and stopover of trans-Saharan spring migrant passerines caught at a site in southern Morocco

Abstract

To answer the question whether and how migrating songbirds use the first vegetated areas in southern Morocco after crossing the Sahara Desert in spring, before continuing their northward migration successfully, we investigated the body condition and phenology of birds captured at a stopover site in Tafilalt from 2 April to 3 May 2005. The median date of passage of all Palaearctic species combined was 13 April. Only Pied Flycatchers Ficedula hypoleuca clearly peaked later, on 22 April. Of the seven species caught most often, only Pied Flycatchers were mostly in good-enough condition to reach Europe without refuelling, whereas in the other species most of the birds would have needed to refuel before crossing the Mediterranean. The majority of Northern Wheatears Oenanthe oenanthe and Woodchat Shrikes Lanius senator were in poor body condition and would have needed to refuel to continue their flight further north, but the low recapture rates suggest that these species stored only enough fat to reach the next available stopover sites rather than to fuel a longer flight north. Within all species, the recapture rate of birds staying longer than one day was low (2.9%) and most of the recaptured birds were in relatively good condition when first caught, indicating that their longer stopover time was not enforced by poor body condition. In general, our study showed that these stopover sites immediately north of the desert may not offer optimal refuelling opportunities for reaching northern destinations and that for many birds they are used simply as a temporary refuge to recover from fatigue or, in some species, as a necessary refuelling site, albeit suboptimal, in order to reach better refuelling sites further north.