During the breeding seasons of 1991-96, nest-site selection by Varied Parus varius and Great tits P. major was studied in a secondary forest in southeastern Kanagawa Prefecture, Japan. Great Tits were found to prefer nest-boxes in areas with a relatively low degree of shrub layer cover, whereas Varied Tits selected nest-boxes in areas with a relatively high degree of shrub cover. Forest management which involves clear cutting the shrub layer is, therefore, inappropriate for the Varied Tit.

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Habitat selection by Ijima's Willow Warblers Phylloscopus ijimae was studied on Miyake-jima (Miyake Island) in the Izu Islands, in the western Pacific Ocean. In order to investigate the relationship between the density of warblers and landscape, we selected three study sites in different landscapes, and compared the density of warblers among them. Forest type did not influence warbler density. The lowest density of warblers was recorded at the site that was heavily fragmented by agricultural fields. Warbler habitat was analysed at a fine scale (50 m x 50 m quadrats), and a stepwise multiple regression analysis was employed to analyse the relationship between warbler density and the vegetation characters. Three factors, tall tree cover, forest edge length, and forest type were adopted as explanatory variables by the analysis. At the fine scale, well-developed continuous laurel forests have the greatest carrying capacity density of for Ijima's Willow Warblers. The results of this study show that Ijima's Willow Warblers are particularly associated with welldeveloped continuous forests, and that laurel forest provides more suitable habitat for them than does deciduous forest.

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The sex ratio of 137 fledglings, from 91 broods, of Blakiston's Fish Owls Ketupa blakistoni raised in Hokkaido, Japan, over the period 1985-99, was analyzed. The sex ratio of fledglings was significantly male-biased (81 males. and 56 females; P=0.04) although no significant difference was detected when it was compared to the expected value (50% males) for each brood size (one or two). Logistic regression analysis did not reveal any significant effects of the locations of breeding sites on the sex ratio of fledglings. Young male owls suffered higher mortality than females. It is suggested that the male-biased sex ratio at fledging is moderated toward parity during the post-fledging stage. Factors considered to attribute to the skewed sex ratio at fledging of Blakiston's Fish Owl were: sexual dimorphism, local resource competition (LRC) and demographic stochasticity resulting from the small population size. Sexual dimorphism suggested that the male-biased sex ratio of fledglings was qualitatively consistent with Fisher's theory. However, sexual dimorphism alone does not quantitatively explain the male-biased sex ratio in Blakiston's Fish Owls. Differential natal philopatry between the sexes suggests that LRC is occurring. The small population size of the Hokkaido population is considered to be the most alarming factor from a conservation point of view.

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An index of body condition was calculated as the residual from the regression of the cubed root of body mass against the first principle component score of a principle component analysis of six external measurements, which was represented as total body size. This index was called the residual body condition index, or RBCI. To evaluate the utility of the RBCI in studies of Leach's Storm-petrels (Oceanodroma leucorhoa), the RBCI was compared to measurements of total lipid mass. Total lipid content was extracted using ethyl-ether after birds had been killed under anesthesia. The RBCI explained 57.4 % of the variation of the cubed root of total lipid mass. We could thus reasonably estimate the body condition of the parents breeding under natural conditions by measuring their body mass and external measurements.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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