| Abstract: | Capsule Both species selected particular patches for roosting, and Linnets but not Corn Buntings showed a social structure with males occupying the preferred roosting positions. Aims To evaluate microhabitat preferences of Linnet and Corn Bunting within a winter communal roost, and to examine roost structure according to sex, age and body size. Methods We captured Linnets and Corn Buntings along a habitat gradient in a reed-bed in central Spain when they were coming to roost. Each bird was sexed, aged, and several body traits were measured. We also characterized the habitat patches where the birds were trapped and grouped patches according to their similarity. Results Three groups of patches were defined according to reed structure. Linnets preferred patches with low density of high and thick shoots, while Corn Buntings preferably used patches with intermediate values for these variables. Interspecific competition for preferred positions was not evident. Male Linnets were proportionately more abundant in the preferred patches, and individuals in lower body condition, independent of sex, age or body size, occupied the non-preferred patches. Male Corn Buntings were less abundant, bigger in size, and showed better condition than females, although differences in body size and condition were not apparent among patches within the roost. Conclusion Our results suggest that among-patch differences in structure and location within a reed-bed generate microhabitats that differ in quality for roosting passerines. This habitat heterogeneity in turn seems to be responsible for the social spatial structure observed in Linnets, in which females and individuals in poor physiological condition were displaced, possibly through competition, towards non-preferred positions. The relatively small body size of Linnets compared to Corn Buntings might explain Linnets' preference for patches that seem to provide more protection against harsh weather conditions. |
