The structure of a local population and dispersal pattern in the Styan's grasshopper warbler,Locustella pleskei |
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Authors: | Hisashi Nagata |
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Institution: | (1) Department of Biology, Kyushu University 33, 812 Fukuoka, Japan;(2) Present address: Laboratory of Wildlife Conservation, National Institute for Environmental Studies, 16-2 Onogawa, 305 Tsukuba, Ibaraki, Japan |
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Abstract: | The breeding sites of Styan's grasshopper warblers are restricted to small islands and distributed discretely. The study on
the marked population was conducted on two islets, Okitsu-jima and Ohtsukue-jima, located near Fukuoka, Japan, from 1981 to
1989. About 20 and 70 birds bred on the two islets, respectively, and the mean density of breeding pairs was 25.5 ha−1. The dispersal pattern and population, structure were examined. Adult birds returned to the same breeding site. Males always
reoccupied the same territory as in previous years but females not. Males were more philopatric and only female yearlings
dispersed over long distances and moved between the breeding sites in Hakata Bay. The returning rate was 0.57 for adults,
and 0.21 for juveniles. The age distribution of birds at Ohtsukue-jima was almost stable, while that at Okitsu-jima was unstable
because it was a marginal habitat for the birds. Estimating from the dispersal pattern and age structure of this warbler the
population near Fukuoka consists of only four islets and is almost stable. |
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Keywords: | age distribution breeding dispersal isolated population Locustella pleskei philopatry |
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