Abstract
In Kyushu, southwestern Japan, the introduced population of the Red- billed Leiothrix Leiothrix lutea has increased rapidly and its range expanded consid- erably since early 1980s. In order to clarify the influences of Red-billed Leiothrix on native bird species, we examined the similarities and differences in foraging patterns among species occurring in a deciduous broadleaved forest on the Ebino Plateau, dur- ing the breeding seasons from 1997 to 2000. Leiothrix foraged in a lower vegetational layer with bamboo, intermediate in height between the foraging levels of the Japanese Bush Warbler Cettia diphone and various Parus species. Foraging height, extent of foraging on deciduous trees and foraging technique were major factors best distinguishing Leiothrix from native species. Seg- regation of foraging niche was distinct and no apparent niche shift, due to invasion of the new species, was detected. Aerial insects tended to be more abundant just above bamboo, mainly about one meter above the canopy, than above bare ground. Thus, jumping, a specific technique used by Leiothrix, is effective for capturing aerial in- sects or agile invertebrates resting on leaves and twigs. Aerial insects were found to be abundant in the foraging space preferred by Leiothrix. Gleaning and hanging, tech- niques mainly used by native species, are suitable for capturing prey of low mobility such as Lepidoptera larvae. Probably due to morphological constraints, Parus spp. and Japanese Bush Warblers seldom foraged by jumping, indicating that they exploit quite different food resources from those utilized by Leiothrix despite their foraging spaces overlapping to some extent. In the deciduous broadleaved forests of Kyushu, an avian guild of foraging aerial in- sects in intermediate and lower layers of the forests is poor. Such a community may be subject to the successful invasion of the Red-billed Leiothrix into native forests.
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