Experimental Analysis of Nest Predation: Effects of Habitat and Nest Distribution

Depredation of artificial avian ground nests was studied in 1994 and 1995 on cool-season and warm-season grasslands in western New York State. The study examined the effects of habitat type and distance from forested edge on nest success in adjacent fields. Two experiments were conducted. The first examined the effects of nest distribution on nest success. Experimental predation rates were highest at the field-forest boundary, although there was no correlation between predation rate and distance from edge. Overall predation rates for cool-season grasslands differed significantly between years, with predation rates being higher during the 1995 field season. The second experiment examined the effects of dense nesting cover on nest success. Predation rates for nests in dense nesting cover varied among distance classes in 1995 but not in 1994; predation rates were also higher in 1995 than in 1994. Experimental rates of nest predation were similar in pasture/cool-season grasslands and warm-season grasslands in both years, suggesting that dense cover did not improve productivity of ground-nesting birds. Indirect evidence suggested that the primary predators along the forest-field boundaries were mammals, with birds and small mammals most frequently depredating nests away from the edge. This study suggests that dense nesting cover does not increase nesting success for small passerines on our study site