Ratsnake response to bottomland flooding: Implications for avian nest predation

Lower predation has been documented for birds' nests located over water and a recent study found lower predation on wood duck (Aix sponsa) nests in bottomland forest during flooding. In a three-year study we used radio telemetry to determine whether flooding affected use of bottomlands by ratsnakes (Elaphe obsoleta) and thus might explain reduced nest predation. Of the 22 ratsnakes we tracked, only five used bottomlands and three of them did so exclusively, suggesting a surprising degree of habitat specialization by individual snakes. Those individuals regularly moved into flooded forest and their frequency of movement and distance moved appeared unaffected by flooding. Although it seems unlikely that ratsnakes leave bottomlands during floods, they may prey more extensively on small mammals that are restricted to trees when the forest is flooded, thereby reducing predation pressure on nesting birds.