Species-specific distribution of reed-nesting passerine birds across reed-bed edges:: Effects of spatial scale and edge type

We studied the distribution of breeding passerine birds across reedbed edges in Hungary. Our aim was to investigate the effects of edge. Therefore, we studied the birds' distribution at two spatial scales, across four different reed edges (a reed - water edge, a reed - boat path edge, a reed with bushes - dike edge and a gradually changing edge), where the vegetation structure and the landscape position (depending on the extent of open water) were different. Reed-nesting birds were censused by the line transect method in three wetlands (Lake Velence: 1992-1994; Kis-Balaton: 1991; Macska-sziget (island), Szigetkoz: 1994-1995). We found different edge effects at different spatial scales. At the landscape scale there were no differences at the community level between edge and interior community structure parameters (species number, total and species density), but at the species level, the density of Bluethroat Luscinia svecica was 3.5 limes higher in the interior than in the edge habitat, whereas the density of Great Reed Warbler Acrocephalus arundinaceus was 12 times higher in the edge than in the interior habitat. At the local scale, when only the first 40 m from the edge was considered, the Reed Warbler A. scirpaceus, Savi's Warbler Locustella luscinioides, Bearded Tit Panarus biarmicus and partly the Sedge Warbler A. schoenobaenus showed strong significant edge (0-5 m) preference for both reed - water and reed - boat path - reed edges. Eight out of 14 species showed different patterns of edge avoidance/preference at the three edges of similar landscape position, which reflects the crucial role of vegetation structure at the edge. Reed-nesting passerine species responded individualistically to edges. The general pattern of edge preference on the local spatial scale may be a result of fewer nest predation in the edges mediated by the vegetation structure.