Abstract
I recorded the seasonal fluctuations of abundance for Eastern Marsh Harriers Circus spilonotus and Hen Harriers C. cyaneus wintering at two sites in Okayama Prefecture from 2011 to 2014. Individuals were identified by external plumage and morphological characteristics. The peak period for arrival of Eastern Marsh Harriers was between October and December each year. The peak of their roosting abundance was between October and February, when the arrival of newcomers augmented the number of regularly observed individuals. The peak of roosting abundance in Hen Harriers, on the other hand, was reached between December and January. This period for peak numbers of roosting Hen Harriers was different from that of other wintering sites in Japan. The peak of roosting abundance for Hen Harriers is assumed to be influenced by the location of the roost site relative to the migration route.
