Effects of Forest Fragmentation on Depredation of Artificial Nests

Abstract

Depredation on artificial ground and arboreal (1.5 m above ground) nests was studied in mature (uncut) forest stands on a ruffed grouse (Bonasa umbellus) management area in central Pennsylvania from May to August 1986. Predation was evaluated in mature stands with zero, 25, and 50% zones of the surrounding forest fragmented by clearcutting. Nest depredation was highest in the 50% zone and least in the zero percent zone; more arboreal nests than ground nests were disturbed. American crows (Corvus brachyrhynchos) were major predators on nests in the 50% zone, and crows and blue jays (Cyanocitta cristata) caused most nest disturbances in the 25% zone. Our results suggest that fragmentation of surrounding mature forest stands may negatively impact avian nesting success, especially when the principal nest predators are corvids. Predation in fragmented forests may have a greater effect on nesting success of birds nesting above ground than on those nesting at ground level. J. WILDL. MANAGE. 52(1):158-161 Forest fragmentation, or the cutting of remaining natural forest into progressively smaller patches (Harris 1980), negatively impacts abundance and distribution of insectivorous passerines in the eastern United States (Whitcomb et al. 1981). Because forest fragmentation results in greater edge (Ranney et al. 1981) and predators select edges for foraging (Gates and Gysel 1978, Chasko and Gates 1982), predation on avian nests could increase with extensive forest fragmentation (Noss 1983). However, with the exception of a study dealing with predation on artificial nests in woodlots of various sizes (Wilcove 1985), the influence of forest fragmentation on nest predation is not well documented. Clearcutting forest to improve ruffed grouse habitat at the Barrens Grouse Habitat Management Study Area (BGMA) in central Pennsylvania provides suitable nesting habitat for a variety of avian species that nest ?2 m from the ground (Yahner 1986b, Yahner and Cypher 1987). The BGMA contains a sector with no forest fragmentation (zero clearcutting) and sectors with 2 intensities of forest fragmentation (25 and 50% clearcutting) that provided an opportunity to examine the relationship between nest depredation and forest fragmentation. Our objective was to compare depredation on artificial ground and arboreal nests placed in mature forest stands surrounded by uncut forest and 2 intensities of forest fragmentation at the BGMA. We thank R. A. Voytko and R. W. Bond for field assistance. Funding for this study was provided by the Max McGraw Wildlife Foundation and the Pennsylvania Agricultural Experiment Station. W. A. Creed, R. G. Eckstein, and M. J. Lacki reviewed the manuscript. This is Journal Series Paper 7565 of the Agricultural Experiment Station, The Pennsylvania State University, University Park.