Nest predators can adversely affect the viability of songbird populations and their impact is exacerbated in fragmented habitats. Despite substantial research on this predator-prey interaction, however, almost all of the focus has been on the birds rather than their nest predators, thereby limiting our understanding of the factors that bring predators and nests into contact. We used radio telemetry to document the activity of two snake species (ratsnakes: Elaphe obsoleta; racers: Coluber constrictor) known to prey on nests in Midwestern bird communities and simultaneously monitored 300 songbird nests to test the hypothesis that predation risks should increase for nests when snakes were more active and in edge habitat preferred by both snake species.
Results/Conclusions
Predation risk increased when ratsnakes were more active, for all nests combined and for two of the six bird species for which we had sufficient nests to allow separate analyses. This result is consistent with ratsnakes being more important nest predators than racers. We found no evidence, however, that nests closer to forest edges were at greater risk. These results are generally consistent with the one previous study that investigated ratsnakes and nest predation simultaneously. The seemingly paradoxical failure to find higher predation risk in the snakes’ preferred habitat (i.e., edge) might be explained by the snakes using edges at least in part for non-foraging activities. We propose that higher nest predation in fragmented habitats (at least that attributable to snakes) results indirectly from edges promoting larger snake populations, rather than from edge directly increasing the risk of nest predation by snakes. If so, the notion of edges per se functioning as ecological “traps” merits further study.
