Breeding and Foraging Ecology of Ospreys at the Yoshino River

Abstract

. We studied the ecology of Ospreys Pandion haliaetus from 1998 to 2000, along a 30 km east to west stretch of Tokushima Plain, from a 3 km section of seacoast to 27 km up the Yoshino River. Ospreys, including wintering birds, were resident throughout the year and numbered 10 to 20 birds. In the breeding season of 2000, six pairs nested and at least eight chicks fledged successfully. Five of the six nests were dispersed loosely-colonially with-in a few kilometers of each other. The prey were fish, both marine and freshwater species. The main hunting sites were just below the Daiju Dam throughout the year, and the seacoast area in the non-breeding season: the former 2 km area supplied 43 ％ of total food to the Osprey population during the breeding season. Hunting sites of loosely-colonial pairs overlapped markedly and were concentrated just below the Daiju Dam. Large numbers of fishes seemed to be aggregating there, making this location an attractive hunting site for Ospreys.