A study on the influences by introduced birds on native birds.

引进鸟类的归化一直是世界各地本土物种生物多样性保护中的一个严重问题。在日本，虽然有不少外来鸟类建立了归化种群，但对这一问题的生态学研究很少。在这项研究中，我阐明了最成功的引种之一的红嘴林莺的生态及其对同域本地鸟类，特别是日本灌木林莺繁殖的影响。只有这两个物种是在矮小的竹子灌木丛中繁殖的。虽然大多数灌木莺的巢位于茂密的竹丛栖息地，但Leiothrix筑巢在密度范围更大的灌木丛中。栖息地选择的通用性是其数量迅速增加的原因之一，其繁殖期比其他共生物种长得多。这两个物种的繁殖成功率都很低，一个主要原因是松鸦和蛇的捕食。Leiothrix主要在低层森林中的高大树木的树叶和树枝上觅食，与灌木林莺主要在灌木丛中觅食。落叶阔叶林地上矮化竹丛、低层取食、繁殖期长等生态位空缺，使落叶阔叶林和有偿树种的取食空间垂直范围重叠较大，但存在水平分离现象，并呈上升趋势。梅花鹿已经将Leiothrix和灌木林莺的栖息地分割开来。随着栖息地破碎化的进展，有必要对这两个物种的种群动态进行监测。

Naturalisation of introduced birds has been a serious problem in the conservation of biodiversity of native species throughout the World, In Japan, although not a few species of exotic bird species have established naturalised populations, there have been few ecological studies on this problem. In this study, I clarified the ecology of the Red-billed Leiothrix, one of the most successful introduced species, and its influence on the breeding of sympatric native bird species, particularly the Japanese Bush Warbler.The Leiothrix was the most dominant species among the forest living bird community and outnumbered the Bush Warbler. Only these two species bred in the bush of dwarf bamboo. While most nests of the Bush Warbler were located in the habitats of dense bamboo bush, the Leiothrix nested in bushes of much wider range of density. The generalistic habit of habitat selection is one of the reasons for the Leiothrix to have been increasing the number rapidly.The breeding season of the Leiothrix was much longer than those of other sympatric species. The breeding success was very low in both species, a main cause being the predation by the Jay and snakes.The Leiothrix foraged mainly on leaves and twigs of tall trees in the lower layers of forests, segregating from the Bush Warbler foraging mainly in the bush. The overlap of vertical range of foraging space between the Leiothrix and paid species was large, but there was the horizontal segregation between them.The Leiothrix has been increasing because they occupied a vacant niche, i.e. bush of dwarf bamboo in the floor of the deciduous broadleaved forests, foraging in the lower layers of the forests and long breeding season. The habitats of the Leiothrix and Bush Warbler has been fragmented by the Sika deer. It is necessary to monitor the population dynamics of these two species with the progress of the habitat fragmentation.