Effects of Nest Location on Depredation of Artificial Arboreal Nests

Abstract

Depredation on artificial arboreal nests was studied in 1-ha aspen (Populus spp.) plots on a ruffed grouse (Bonasa umbellus) management area in central Pennsylvania from May to August 1985. Predation was evaluated with respect to 2 factors associated with nest placement: height of nest aboveground and plot age. American crows (Corvus brachyrhynchos) were the major nest predator. Fewer low nests (0.5 m aboveground) were disturbed than high nests (1.5 m), and more nests were disturbed in both 8-year-old and mature plots than in 4-year-old plots. Low nests in 4-year-old plots were least susceptible to depredation. Dense shrub growth in 4-year-old plots presumably reduced the foraging efficiency of predators, thereby lowering the probability of disturbing low nests. Young clearcuts provide well-concealed nest sites for avifauna that construct nests near ground level in shrubby vegetation. J. WILDL. MANAGE. 51(1):178-181 Predation is a major factor reducing nesting success in birds (Ricklefs 1969). Avian predators may have a greater impact than large mammalian predators on nests located high in small trees and shrubs than nests positioned close to ground level (Joern and Jackson 1983, Shalaway 1985). The relationship between nest height and susceptibility to disturbance by predators may vary with habitat type. For instance, Caccamise (1977) found that in tidal marshes, the percentage of successful nests decreased as nest height increased, whereas Best and Stauffer (1980) noted that fledging success was greater in higher nests (1-2 m aboveground) compared to that of lower nests (<1 m) in riparian habitats. In general, avian nests, particularly those located near ground level, may be less conspicuous to predators when located in areas with complex vegetative structure (Bowman and Harris 1980, Redmond et al. 1982, Yahner and Wright 1985). An even-aged system of forest clearcutting provides suitable habitat for a variety of songbird species that construct nests near (<2 m) ground level (Yahner 1986b). The objective of this study was to compare depredation on artificial arboreal nests placed at 2 heights above ground level in small aspen plots of 3 age classes (time since clearcutting) and, hence, different vegetative structure. We thank E. A. Cypher and R. L. Schooley for field assistance and L. B. Best, D. P. Scott, and R. D. Shipman for comments on the manuscript. This study was supported by the Pa. Agric. Exp. Stn. and the Max McGraw Wildl. Found. This is J. Ser. Pap. 7417 of the Pa. Agric. Exp. Stn., The Pennsylvania State Univ., University Park.