Spatial distribution and habitat use of reed warblers Acrocephalus scirpaceus during the autumn migration

Spatial behaviour and habitat selection at stopover sites have a strong influence on the foraging and fuelling performance of migrating birds and hence are important aspects of stopover ecology. The aim of this study was to analyse the spatial behaviour and habitat use of reed warblers Acrocephalus scirpaceus during the autumn migration. We used radio tracking data from reed warblers surveyed at a stopover site in northern Iberia and assigned to three different groups: (1) local adult birds which were still at their breeding site, (2) migrating first-year birds (originating from beyond Iberian peninsula) and (3) migrating adult birds. Overall, migrating first-year birds tended to have larger home ranges than both local and migrating adults and to move more widely in the study area. They also showed lower fat deposition rates than adults. The proportion of habitats in home ranges (reed-beds and tidal flats being the most abundant habitats) was similar amongst groups. The spatial distribution and habitat use of organisms have been theorised to follow an ideal-free or ideal-despotic distribution. However, according to our results, other complex underlying mechanisms may play an important role in shaping the spatial behaviour of birds at stopover sites.