Breeding Biology of Corvus corone and C. macrorhynchos in central Hokkaido

Abstract

Nest distribution, nesting sites, breeding periods, sexual organs and nutritive conditions of two species of crows, Corvus corone (CC) and C. macrorhynchos (CM), were studied during 1989 and 1990 in Obihiro and its surrounding areas in three types of habitats: residential areas with no wooded areas (RI); residential areas with woods (R2), and agricultural land (AL). Thirty seven CC nests and 8 CM nests were examined during the study. CC nested mainly in shelterbelts in AL and on road side trees in R 1 and R2. CM nested mainly in woods in AL and R2. Nest densities of both species were high in R2 and low in AL.•Distances between neighbouring nests were shorter in Rl and R2 than in AL. Though the breeding period, from nest-building to fledging, was about 100 days both in CC and CM, CC started to breed 18 to 24 days earlier than CM. The testes and ovaries of CC began to enlarge earlier than those of CM. Nutritive conditions did not vary during the year for either species, and no relationship between onset of breeding and body weight or nutritive condition was found. The discrepancy in onset of breeding between CC and CM is probably due to their different reactions to the same daylight condition.