Settlement and fat accumulation by migrant pied flycatchers in spain

Abstract

Pied Flycatchers migrating through Spain showed a marked tendency to settle in some areas. During the stay their weight and fat reserves increased. The density of settled birds and some unidentified seasonal features were major factors determining the settling rate of newly arrived birds. The level of fat reserves at arrival also seemed to be involved in the decision as to whether to stay or not. The tendency to settle was stronger in juveniles than in adults, apparently as a consequence of their lighter weight on arrival. The length of stay was related to the rate of gain in weight. The role of age-related factors on the decision to depart is discussed in the light of differences between the settlement and movement patterns of juveniles and adults. © 1986 Taylor & Francis Group, LLC.