EFFECTS OF FOREST FRAGMENTATION ON A GUILD OF WINTERING PASSERINES - THE ROLE OF HABITAT SELECTION

This study analyses the winter colonization of an archipelago of 31 fo rests (0.1-350 ha) in central Spain by the guild of pariforms (Parus, Aegithalos, Regulus, Sitta and Certhia). Two hypotheses are considered (a) that birds with similar habitat preferences tend to disappear sim ultaneously with the reduction in forest size, leading to a 'nested' p attern of species distribution; or (b) that the species in the smalles t forests are a random sample of those found in the larger ones. The r esults support hypothesis (a). The species that depend on relatively s carce resources, such as tree trunks and junipers Juniperus thurifera (Sitta europaea, Certhia brachydactyla, Parus cristatus and P.ater) on ly occupied the largest forests. On the other hand, species that explo it abundant, ubiquitous resources, such as helm oak Quercus ilex folia ge (Regulus ignicapillus and Parus caeruleus), were distributed unifor mly throughout all the fragments. These results emphasize the need for a better understanding of habitat selection by species when designing conservation strategies for fragmented populations.