DEPREDATION RATES AND PREDATORS AT ARTIFICIAL BIRD NESTS IN AN UNFRAGMENTED NORTHERN HARDWOODS FOREST

Spatial and temporal patterns of predation on birds' nests must be und erstood to determine their effects on bird populations. We used artifi cial bird nests containing Japanese quail (Coturnix japonica) eggs to examine effects of forest strata (ground, shrub, subcanopy), time of s eason (early vs. midsummer), and habitat (deciduous vs. mixed conifero us-deciduous) on nest depredation rates in an unfragmented and relativ ely undisturbed temperate forest in the White Mountains, New Hampshire . We found that depredation rates differed significantly and most stro ngly among forest strata (P < 0.002), with nests on the ground having the lowest rate of depredation (31-46%) and those in the shrub layer h aving the highest (73-88%). Seasonal and habitat variation were also e vident, but no consistent trends were found between early and midsumme r or between habitats. Depredation rates at artificial nests in shrub and subcanopy strata were 2-3 times higher than depredation of real bi rds' nests in those same strata in the same years. Using cameras at a separate set of artificial nests on each plot, we identified 7 predato r species, of which the red squirrel (Tamiasciurus hudsonicus) was the most frequent in 1990 and the fisher (Martes pennanti) in 1991. Stati stical and photographic evidence suggested that fisher in 1991 located and depredated artificial nests systematically possibly by following human scent. These results identify the importance of nest strata, sea son, and composition of the predator community for the nesting success of forest songbirds in large tracts of undisturbed forest, and emphas ize several important potential biases in studies using artificial nes ts.