Condición corporal de paseriformes transaharianos en un palmeral del sureste de Marruecos durante el periodo de paso migratorio prenupcial Body condition of trans-Saharan passerines in a palm tree grove from south-eastern Morocco during the spring migration period

Understanding to what extent northern Africa is used as a fuelling region by Afro-tropical European birds is of great importance from both an ecological and conservation standpoint. In this work we analysed number of captures, fuel load and fuel deposition rate of several species of Afro-tropical European passerines captured during the spring migration period at Zouala, an oasis from south-east Morocco situated ca. 100 km north of the northern Sahara border. The aim was to contribute to understanding how passerines use oases from north Africa during the spring migration period. We captured 46 species overall. From them, 38 were passerines, 23 of which were trans-Saharan. We obtained 820 captures. A 96% of them were passerines, and a 62% were Afrotropical European migrant. Thus, bird assemblage was remarkably influenced by migrant passerine species. A 30% of the captures was monopolized by a single species (Iduna opaca). Overall, fuel loads were lower than registered both in northern Morocco and the western Mediterranean islands. Species with less fat were those that breed in southern Europe or northern Africa. Body mass of birds captured after dawn was lower than those captured before dusk, supporting some degree of mass accumulation, probably as fuel. This increase of body mass gain, however, was not detected when we analysed mass accumulation in individual birds, likely due to the small sample sizes. Similarly, we observed that, except in Phoenicurus phoenicurus, body mass did not increase during the stay in the area. Again, sample sizes here were small, so this result must be interpreted very cautiously. •