Relative status of two species of migrant sparrowhawks on Java and Bali, Indonesia

Every autumn thousands of sparrowhawks, mainly the Chinese Sparrowhawk (Accipiter soloensis) and the Japanese Sparrowhawk (A. gularis), migrate from East Asia to western Indonesia. However, the relative abundance of these two species in Indonesia differs between studies, with some reporting Japanese Sparrowhawk being up to ten times more common than Chinese Sparrowhawk, while other studies report the reverse. We assessed the status of these two migrant sparrowhawks on the islands of Java and Bali by comparing four datasets: data from four watch-sites (1992-2004, 108 days, 7698 birds), general surveys (1980-2004, 354 days, 578 birds), museum collections (< 1820-1957, eight collections, 274 birds), and the literature (1902-2004). In the first three datasets, Chinese Sparrowhawk was 2-10 times more numerous than Japanese Sparrowhawk, and data from the literature tended to support this. There were small but significant differences between the two islands, with Japanese Sparrowhawk being slightly more common on Bali than on Java. Systematic study of all available data on the relative abundance of the two species shows there is no evidence that changes in species composition have occurred.