Since human settlement of the Ogasawara Islands in the early 19th century, several bird species have become extinct owing to the impact of the introduction of non-native species, and other factors. In particular, on the island of Hahajima, seabird breeding colonies have been devastated. This study aimed to determine the relationship between the endemic subspecies of Eastern Buzzard Buteo japonicus toyoshimai and various non-native rats on Hahajima, Ogasawara Islands, Japan. Over a period of 5-10 years video-recordings were made of food being delivered to buzzard nests at three study sites on Hahajima. Rats Rattus spp. were the most abundant prey delivered to the nestlings, accounting for 71-91% of prey items and 83-96% of prey weight; next in abundance was the introduced Green Anole Anolis carolinensis, 6-21% in number. However, since anoles are much smaller than rats, even at the study site where a high proportion of anoles were delivered, the buzzard pair there did not consume fewer rats than at the other sites. Only a small number of birds (1-6%) were delivered to the nests. At one site, where breeding occurred seven times during the study period, there was a significant positive correlation between the number of rats delivered to the nest during the nestling period and precipitation in the October before breeding and in January of the year of breeding.
Abstract. We investigated the reproductive success of Mountain Hawk-Eagles Nisaetus nipalensis between 1990 and 2008 in Yamagata Prefecture, northern Japan. The existence of a correlation between fluctuations in Japanese Beech Fagus crenata seed production and nesting success was verified using observations of breeding attempts. A generalized linear mixed model (GLMM) was used to examine the relationship between nesting outcome and environmental factors (forest type, complexity of forest edges, nesting outcome in the previous year, and snowfall). To verify whether environmental factors affecting nesting outcome are influenced by variation in beech seed production levels, we analyzed the relationship between nesting outcome and environmental factors in the following three cases: (1) when beech seed production levels were high, (2) when beech seed production levels were low, and (3) when the beech seed production levels were not classified. Our results indicate that nesting success was significantly higher following a year when the level of beech seed production was high. However, the factor that was most strongly related to nesting outcome was nesting outcome in the previous year. In our study area, predominated by natural forest, when the beech seed production level in the previous year was low, GLMM analysis indicated that natural forest areas had a negative effect on nesting outcome, and artificial forest areas had a positive effect. The factors that affected nesting outcome differed depending on seed production levels in the previous year, and this suggested that the habitat used for hunting and/or the main prey species changed according to beech seed production levels.
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