Breeding of the Eastern Marsh Harrier (Circus spilonotus spilonotus Kaup 1847) was confirmed in the area along the Ishikari River in the Ishikari District, Hokkaido, Japan. Among the eight nests discovered during the 1988 breeding season, eggs were observed in three nests, and chick (s) were confirmed in three other nests. The remaining two nests had no eggs or chicks. One might have been examined before eggs were laid, and the other might have been abandoned. In addition, two other sites were considered to be probable breeding sites, though the nests could not be found. Breeding processes were not pursued because the confirmation of breeding was the main purpose of this investigation. It was noteworthy that two nests had been built of bamboo grasses on the ground amongst dwarf bamboo. The other six nests were built of reeds in reed marshes as is generally known.
