Variation in the stopover duration of Reed Warblers Acrocephalus scirpaceus in Morocco:: effects of season, age and site

To test the prediction that stopover duration reflects the rate of body mass gain during stopover, the relationship between these two parameters was investigated in the Reed Warbler Acrocephalus scirpaceus at two sites in Morocco, Sidi Bou Ghaba on the Atlantic coast, and Kerbacha on the Mediterranean coast. Estimation of stopover duration was made using the recently published method by M. Schaub et al. We investigated effects of age and site on stopover parameters during autumn and spring migration. Stopover duration was longer for juveniles than for adults, longer at the Atlantic site than at the Mediterranean site and longer in autumn than in spring. Altogether, estimated stopover duration was longer than expected from previous studies based on minimum stopover duration. Body mass gain varied inconsistently among site, season and age classes, without a clear relation to stopover duration. This suggests that stopover duration is not dependent only on the rate of body mass gain.