Effects of Bird Feeder Density on the Behavior and Ecology of a Feeder-Dependent Songbird: Patterns and Implications for Disease Transmission

Anthropogenic resource provisioning of wildlife has increasingly been hypothesized to alter pathogen spread. Although bird feeding is the most widespread form of intentional wildlife provisioning, we know relatively little about how the degree of anthropogenic feeding at a site impacts wild birds in ways relevant to disease transmission. We manipulated the density of bird feeders (low versus high) available at otherwise similar sites and tracked the local abundance, body condition (scaled-mass index), feeding behavior, and movement across the landscape in wild house finches (Haemorhous mexicanus), a feeder-dependent species subject to outbreaks of a contagious pathogen commonly spread at feeders. The local abundance of house finches was significantly higher at sites with high feeder density but, surprisingly, finches at high-density feeder sites had poorer body condition than those at low-density sites. Behaviorally, birds at high-density feeder sites had longer average feeding bouts and spent more time per day on feeders than birds at low-density feeder sites. Further, birds first recorded at low-density feeder sites were more likely to move to a neighboring high-density feeder site than vice versa. Overall, because local abundance and time spent on feeders have been linked with the risk of disease outbreaks in this species, effects of bird feeder density on both traits may, in turn, influence disease dynamics in house finches. Our results suggest that heterogeneity in the density of bird feeders can have diverse effects on wild birds, with potential consequences for disease transmission. Master of Science Feeding wildlife has increasingly been thought to change the spread of disease. Although bird feeding is the most widespread form of intentional wildlife feeding, we know relatively little about how much human feeding impacts wild birds in ways that affect disease transmission. We changed the density of bird feeders (low versus high) available at otherwise similar areas and tracked the local abundance, body condition, feeding behavior, and movement across the landscape in wild house finches (Haemorhous mexicanus), a feeder-dependent species subject to outbreaks of a infectious disease commonly spread at feeders. The local abundance of house finches was significantly higher at sites with high feeder density but, surprisingly, finches at high-density feeder sites had poorer body condition than those at low-density sites. Behaviorally, birds at high-density feeder sites had longer average bouts on feeders and spent more time per day on feeders than birds at low-density feeder sites. Further, birds first recorded at low-density feeder sites were more likely to move to a neighboring high-density feeder site than vice versa. Overall, because local abundance and time spent on feeders have been linked with the risk of disease outbreaks in this species, effects of bird feeder density on both traits may, in turn, increase disease spread in house finches. Our results suggest that variation in the density of bird feeders can have diverse effects on wild birds, with potential consequences for disease transmission.