Differences in Bird Communities on the Forest Edge and in the Forest Interior: Are There Forest-interior Specialists in Japan?

Most North American bird species that are less successful in small forests than in large forests, are forest-interior specialists that winter in the tropics. These species have declined in small forests because of high rates of nest predation and brood parasitism near the forest edge. To determine whether migratory forest-interior specialists are also important components of bird communities in Japan, we surveyed bird populations on plots at the edge and in the interior of deciduous forests in Hokkaido and Kyoto. Surveys were conducted during the breeding season in forest fragments using the point count method. We calculated edge indices for the most abundant species in Hokkaido and Kyoto (38 and 18 species, respectively). Among the nine species that were more abundant in interior than in edge plots in Hokkaido were the following tropical migrants: Turdus cardis, Phylloscopus coronatus, and Cuculus saturatus. In Kyoto, the abundance of particular species of tropical migrants was too low to permit statistical analysis. We therefore analyzed the rare species as a group and this group was more abundant in the forest interior than on the forest edge. Three resident species, Garrulus glandrius, Picus awokera, and Bambusicola thoracica, were also more abundant in the forest interior. The most frequent potential nest predator, Corvus macrorhynchos, was more abundant at the edge than in the interior in Hokkaido, but showed the reverse pattern in Kyoto. The abundance of the most frequent brood parasite in Hokkaido, Cuculus saturatus, had a weak positive relation with the abundance of its host species, but was not significantly related to the distance from the forest edge. Therefore, the major negative edge effects in Japan may be due to nest predation by corvids. The impact of negative edge effects, as well as the effect of forest structure, on forest-interior birds in Japan should be the focus of future research.