Abstract
The range of the Brown-eared Bulbul Hypsipetes amaurotis is mostly restricted to Japan and adjacent areas of East Asia. Although bulbuls are very common, no attempt has previously been made to estimate the numbers or density of bulbuls in Japan. We investigated the distribution of bulbul song-posts in southern Ibaraki Prefecture (648 km2) and with that information estimated their population density. We set 32 survey grids (1 km×1 km) in the study area and confirmed a total of 540 bulbul song-posts during the 2007 breeding season. We then estimated the breeding density of bulbuls with the Poisson regression using a variety of environmental factors. Factors positively influencing breeding density were: the area ratios of ‘forest’, ‘dry-cropland or grassland’ and ‘urban area’. Considering that bulbuls are monogamous and only males sing, we estimated there to be a total of 24,634 breeding bulbuls in the study area and a mean of 38 breeding individuals within 1 km2. We then classified the study area into five categories with the cluster analysis based on the proportion of land use within each 1 km grid. The clusters with the highest breeding densities of bulbuls were: (1) forest, (2) urban and (3) dry-cropland or grassland. Because small woodlands are also found in urban areas and dry-croplands or grasslands occur in the study area, our results indicate that the presence of woodlands is important in habitat selection by bulbuls in the breeding season.
