Nest predation in an anthropogenic landscape

Abstract

Wood Thrushes (Hylocichla mustelina) are experiencing widespread population declines. Knowing the relative contribution of predator species to overall rates of nest predation of Wood Thrushes, and understanding how the thrushes are affected by temporal and landscape factors, may be important elements in choosing and devising effective management strategies. We used miniature video cameras to identify nest predators of Wood Thrushes in a highly fragmented landscape in Ontario. Eleven species of birds and mammals were recorded as nest predators. Birds accounted for almost twice as many predation events as mammals, and three species – Brown-headed Cowbird (Molothrus ater), Cooper's Hawk (Accipiter cooperii), and raccoon (Procyon lotor) – accounted for the majority. Species such as American Crow (Corvus brachyrynchos), Blue Jay (Cyanocitta cristata), eastern gray squirrel (Sciurus carolinensis), and Common Grackle (Quiscalus quiscula) that are often speculated to be important nest predators in agricultural and suburban landscapes contributed little or nothing to overall predation rates. We tested hypotheses concerning effects of nest stage, time of nesting season, forest size, forest cover, urban housing pressure, and prior predation events at a nest on the probability of nest predation. Our models showed only two of these factors to be significant: prior predation at a nest increased the chance of a subsequent predation event and increasing the measure of urban pressure reduced the chance of a predation event. The many alternate and easy food sources associated with humans might divert the attention of potential predators from nesting birds in urban forests.