抄録
A total of 3, 000 to 3, 500 Carrion Crows Corvus corone and Jungle Crow C. macrorhycos was captured by "multi-traps" from 1987 to 1990 in Ikeda, eastern Hokkaido. Of trapped crows from July through December 1987, 564 Carrion Crows and 387 Jungle Crows were classified into two age classes, juveniles and adults, on the basis of the presence of bursa of Fabricius, tongue patterns and skull ossification. The percentage of juveniles (Carrion crow 82.4%, Jungle crow 97.2%) was always much higher than that of adults (Carrion crow 17.6%, Jungle crow 2.8%) and the total number of birds captured dependant largely on the number of juveniles in both species. The number of Crows captured decreased to less than 100 bird in May and June, and then increased to the peak of more than 600 birds in November and December. The probable reasons of the seasonal changes are the dispersion of young birds in July and food shortage from October or November.
