Abstract
Carrion and Jungle Crows Corvus corone and C. macrorhynchos are major agricultural pests in Japan, and information about their population dynamics, including breeding success, is necessary for their population and damage control. We investigated breeding success and factors affecting the number of fledglings of these two species in a rural area in and around Tsukuba City, Ibaraki Prefecture, about 50 km north of Tokyo. The proportion of successful pairs was 76% in Carrion Crow, and 87% in Jungle Crow, while the number of fledglings per successful pair was 2.37 in Carrion Crow and 2.62 in Jungle Crow. For both species, the number of fledglings per successful pair decreased as the breeding season progressed. We used generalized linear models to analyze factors affecting the number of fledglings. In Carrion Crow, longer distance to nearest Jungle Crow's nest, higher proportion of foraging area within 150 m of the nest and shorter distance to nearest conspecific nest were contributing factors to increase the number of fledglings. In contrast, no effective models were constructed from our Jungle Crow data set. As Jungle Crows start breeding later, and as the fledgling number seemed unaffected by the distance to the nearest Carrion Crow's nest, Jungle Crows may construct their nests irrespective of the position of Carrion Crow nests. This might be one of the reasons for the shorter distance between heterospecific nests (361 m) than conspecific nests (410 m in Carrion Crow and 451 m in Jungle Crow).
