SEASONAL BODY MASS CHANGES IN PIED FLYCATCHER (FICEDULA HYPOLEUCA) AT TWO STOPOVER SITES IN MOROCCO.

Seasonal body mass changes during stopover were investigated for the pied flycatchers Ficedula hypoleuca stopping over at two sites in Morocco, reed bed in Larache on the Atlantic coast, and Ramsar Smir on the Mediterranean coast. Estimation of stopover duration was done using the recent method by Schaub et al. (2001). We investigated effects of age and site on body mass parameters and to describe the diet in terms of prey composition to further interpret these data in relation to migration strategy during the stopover in Morocco. Body mass and fat reserves all increased markedly during the day since first capture. These changes in body mass were strongly associated with the observed changes in fat reserves. The prey size distribution differed significantly between the two site with birds at reed bed in Larache fed larger prey than at Ramsar Smir.