Species-Specific Adaptability in Seasonal Resource Use by Non-Breeding Crows: Contrasting Responses to Natural and Anthropogenic Environments

Abstract

Crows are birds that have a close association with people. Their frequent exploitation of anthropogenic resources often causes human–wildlife conflict. In Japan, the Carrion Crow (Corvus corone) and the Large-billed Crow (C. macrorhynchos) occur sympatrically and are often treated as a single management unit. However, their behavior and habitat differ by species and breeding status, and explicit comparative evaluations of resource use between sympatric crow species are required for effective wildlife management. We conducted direct field observations of non-breeding individuals of two crow species using GPS transmitter data and recorded foraging sites and food items throughout a year, six bimonthly periods. We then quantified seasonal interspecific differences using a Morisita index-based dissimilarity measure and evaluated the significance with permutation-based randomization. Our study has revealed the detailed year-round habitat use and food resources of the two crow species. From spring through autumn, the foraging site and resource use of the two crow species differed significantly; Carrion Crows primarily used agricultural environments, and Large-billed Crows exploited non-agricultural anthropogenic environments such as livestock facilities. In winter, snow cover constrained food access, and both species relied on anthropogenic resources, including unharvested persimmons in the garden and discarded apples in agricultural fields. No use of household garbage was recorded, suggesting that the pattern of reliance on anthropogenic resources in non-breeding individuals differs from that of breeding individuals. Because non-breeding crows represent a highly mobile segment of crow populations, management efforts that focus on specific resources at critical times are likely to be more effective.