Predation of artificial nests in hardwood fragments enclosed by pine and agricultural habitats

Nesting success of songbirds often is poor in edge-dominated habitats. Because the spatial juxtaposition of forest fragments relative to other habitats may influence nest success, we tested the hypothesis that the depredation rate for bird nests in small hardwood forests mould decrease if the degree of edge contrast with adjoining habitats was reduced. Over 4 trials, we placed 672 artificial nests (336 each at shrub and ground levels divided equally between edge and interior locations) in small (range = 0.5-5.0 ha) hardwood forest stands enclosed by either agricultural fields (n = 7) or mature pine forest (n = 7). Nest predation was greater (P = 0.001) in field-enclosed stands (35%) than in pine-enclosed stands (20%) because of greater (P = 0.03) predation of shrub nests. No differences (P > 0.05) in predation rates were detected between stand types for ground nests or between strata (i.e., ground nests vs, shrub nests) within field-enclosed stands. Predation rates did not differ (P > 0.05) between edge and interior nests between or within stand types. Nest predation by avian species was not suspected in pine-enclosed stands (0%), but 18% of the nests depredated in agriculture-enclosed stands was attributed to birds. The low edge contrast associated with pine-enclosed stands appeared to attract fewer nest predators, especially those that preyed on shrub nests. However, the value of lower predation rates for shrub nests in pine-enclosed stands may be offset by the presence of fewer shrub-nesting sites relative to similar-sized field-enclosed stands, because understory development was impoverished, probably as a result of reduced sunlight penetration.