Supplementing non-target taxa: bird feeding alters the local distribution of mammals

Although the effects of bird feeding on avian species have been extensively examined, few studies evaluate the indirect effects of bird feeding on non-target taxa. Bird seed could provide direct nourishment to several mammalian species (e.g., Lagomorpha, Rodentia, and Cetartiodactyla), potentially altering their distribution and behavior with possible unintended consequences for some avian populations, particularly those not directly benefiting from the resource. To examine how bird feeders may influence the presence and behavior of mammals, we used camera traps to quantify differences in the distribution and richness of mammal species frequenting sites with bird feeders and control sites (lacking feeders) in Ithaca, New York, USA. We recorded 15,684 images capturing 12 mammal species with gray squirrel (Sciurus carolinensis) and raccoon (Procyon lotor) detected significantly more often at feeder sites than at control sites. Detections of white-tailed deer (Odocoileus virginianus) marginally increased near feeders whereas detections of several carnivorous species were unrelated to the presence of bird feeders. We recorded larger gray squirrel and raccoon group sizes and greater mammal richness at feeder sites than at nearby control sites. We detected squirrels and raccoons less when snow covered the ground than on snow-free days. Ambient temperature was not a strong predictor of mammal detections. Camera trapping revealed strong, species-specific patterns in the timing of daily visitation to areas with feeders. Because many mammals depredate bird nests, the local increases in mammal richness and activity near bird feeders may create an ecological trap for avian species nesting in close proximity to supplemental feeding stations.