During the periods from February to July in 1983-1986, the breeding ecology of the Blackeared Kite Milvus migrans lineatus was studied in the vicinity of the Wakimisaki fishing-port, situated at the edge of the Nagasaki Peninsula, Nagasaki Prefecture, Kyushu. The results obtained are summarized as follows:
1) In 1985 and 1986, the number of pairs inhabiting the study area (ca. 0.4 km²) was found to be 33 each year. Such aggregation of pairs seemed to be due to abundant food available at the fishing-port and plentiful trees suitable for nesting on the nearby hill.
2) The breeding success was determined based on 32 nests examined in 1983-1986. Of the 32 nests, 28 contained at least one egg, and the mean clutch size was 2.2. At least one nestling fledged at 24 nests. The mean number of fledglings was 1.0 per nest, and this breeding productivity seemed sufficient to maintain a stable population.
3) The behaviour of the parents was observed during the period from incubation to postfledging. The female parent spent almost all the time within the territory until the early postfledging phase. Although she resumed to hunt within or near the territory during and after the middle nestling phase, the prey animals were chiefly foraged by the male parent, suggesting that in such an area provided with abundant food, the male parent was able to supply enough food for his family by himself.
4) From the above it is concluded that in an area with a plenty of food and nesting trees, the kite can nest aggregatively and produce sufficient young to maintain a stable population, and that the female parent remains within the territory during the time from the incubation period to the early post-fledging phase because of the sufficient supply of food by the male parent.