Eastern Buzzard Buteo japonicus toyoshimai Breeding on the Ogasawara Islands Depend on Non-Native Rats as a Food Source

Abstract

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.