Autumn body condition of Palaearctic trans-Saharan migrant passerines at an oasis in southeast Morocco

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Abstract
To improve knowledge of the different migratory strategies used by European trans-Saharan migrants to cross the Sahara Desert in autumn and the role of desert oases, we collected field data on body condition and stopover behaviour at Yasmina, a tiny oasis in southeast Morocco. Of 13 species studied, those best adapted to dry habitats, with breeding ranges mostly in the Mediterranean or North Africa and wintering in the Sahel (Saharan Olivaceous Warbler Iduna pallida reiseri, Western Olivaceous Warbler Iduna opaca, Subalpine Warbler Sylvia cantillans and, perhaps, Rufous-tailed Scrub Robin Cercotrichas galactotes), arrived at Yasmina with, at best, moderate fuel loads but appeared to be the most prepared to refuel en route to their winter quarters; at least part of the population of the Reed Warbler Acrocephalus scirpaceus seemed to follow a similar strategy. Strategies were more diverse among species linked more to mesophilic vegetation; Common Redstart Phoenicurus phoenicurus, Garden Warbler Sylvia borin and Blackcap S. atricapilla tended to arrive with enough fuel reserves to reach the Sahel without additional fattening, but Willow Warbler Phylloscopus trochilus, Spotted Flycatcher Muscicapa striata and Pied Flycatcher Ficedula hypoleuca carried only intermediate fuel loads, which were in most cases insufficient to avoid further refuelling. Although feeding en route may play an intrinsic part of the migratory strategy of the Spotted Flycatcher it remains unclear whether or not this is the case in the other two species.

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