Abstract
From February 1979 to February 1991 at Obihiro, eastern Hokkaido, 69 Turdus naumanni (TN) and 14 T. obscurus (TO) were captured and ringed with a numbered metal ring. TN were captured in spring and autumn migratory seasons, and during the winter. TO were captured only in the autumn migratory season. Numbers of birds captured per net-days differed from year to year. Birds were recaptured only within the season they were ringed. The average body weight of TN was 75.7g in October and 77.4g in February, decreasing slightly to 73.2g in March. Prior to the spring migration, body weight increased significantly to an avarage of 94.6g in May. The average body weight of TO was 65.9g September and 65.2g in October.
