Birds in a Farmland—More Species in Small than in Large Habitat Island

Birds were censused on habitat islands to investigate the effect of vegetation, island size, and isolation on the density and species diversity of birds. The density of birds was highest on small habitat islands and in islands close to other islands, especially large ones. We suggest that this is because birds on small habitat islands utilize resources from surrounding fields. After compensating for sampling effect (the fact that we made more observations and there are more territories on large islands), we analyzed the species richness of different islands. We found that there are more territorial species (i.e., bird species whose territories are readily mapped) on small than on large islands. We discuss different causes for this finding. We also found that a given area comprised of many small islands contains more species than the same area comprised of only a few large islands. This is true for both all observed bird species and for all recorded territorial species. We conclude that, when considering conservation from a local perspective, it is important to protect all nonmatrix land in this type of landscape. This will ensure a high local diversity.