Spring weights and fat deposition of palaearctic passerine migrants in Senegal

Abstract

This paper compares the patterns of weight and fat‐class of Palaearctic passerine migrants trapped at two sites in Senegal in spring 1986. Despite considerable variations in some species (Reed Warbler Acrocephalus scirpaceus and Subalpine Warbler Sylvia cantillans) the great majority of the birds trapped had weights well above the breeding and wintering levels and showed clear evidence of premigratory fattening. In the Yellow Wagtail Motacilla flava and Chiffchaff Phylloscopus collybita some individuals weighed more than twice as much as others. Mean values of fat‐classes of first captures and retraps differed significantly. Species could be divided into two different groups: (a) those (Sand Martin Riparia riparia. Yellow Wagtail and Pied Wagtail M. alba) with small variation in fat classes (12%‐23%), and (b) those (Chiffchaff, Subalpine Warbler, Reed Warbler and Redstart Phoenicurus phoenicurus) showing a high variation in fat‐class (39%‐55%). Birds of the first group had a significantly higher mean fat‐...