Old Nests as Cues for Nest-Site Selection by Birds: An Experimental Test in Small Even-Aged Forest Plots

Abstract

Nest-site selection in birds is a function of various factors, e.g., philopatry, microclimate, degree of concealment from predators, and density and characteristics of vegetation (Welty and Baptista 1988, Gill 1990). Recently, Erckmann et al. (1990) tested experimentally whether old nests were used by Red-winged Blackbirds (Agelaius phoeniceus) as cues to assess the quality of habitat for placement of nest-sites (old-nest hypothesis). They concluded that old nests were of little or no importance as cues in nest-site selection, based on their findings that nest densities did not necessarily increase in plots containing old nests compared to plots without old nests. Moreover, Erckmann et al. (1990) recommended that the old-nest hypothesis be examined in other avian species. Management of small (1 ha), even-aged plots for Ruffed Grouse (Bonasa umbellus) habitat via forest clear-cutting creates suitable habitat for an assemblage of breeding-bird species that are adapted to nesting in brushy vegetation or along edges (Yahner 1987, 1991). Several of these species, such as Gray Catbirds (Dumetella carolinensis) and Field Sparrows (Spizella pusilla), arrive on breeding grounds prior to complete leaf-out of vegetation. Furthermore, above-ground nests established during the previous breeding season in evenaged plots can remain intact on nesting substrate into the subsequent breeding season (R. H. Yahner, pers. observ.). Thus, old bird nests may serve as indirect cues of habitat suitability to these birds when establishing nest-sites (after Cody 1985). If this were the case, then I would predict that birds arriving in spring would preferentially select even-aged plots with higher densities of old nests than those with lower densities. In this study, I tested whether numbers of nests established by birds of all species combined in even-aged plots were affected by removing or increasing the numbers of old nests from the previous breeding season. My study was conducted on a 240-ha portion of the Barrens Grouse Habitat Management Area (HMA), State Game Lands 176, Centre County, Pennsylvania (Yahner 1991). The study area was located within the treated sector of the Barrens Grouse HMA, which was managed by the Pennsylvania Game Commission since 1976 using an even-aged system of forest clear-cutting to create habitat for Ruffed Grouse (Yahner 1991). The study area contained 60 contiguous, 4-ha blocks; each block was subdivided into four 1-ha (100x 100-m) plots arranged in a clockwise pattern (termed plots AD). Plot A (western plot) was clear-cut in winter 19761977, plot B (northern plot) in winter 1980-1981, and plot C (eastern plot) in winters 1985-1986 or 19861987; plot D (southern plot) consisted of 60-year-old forest stands. This resulted in a checkerboard pattern of four age classes in each block (Yahner 1991). Received 27 July 1992. Accepted 29 October 1992. SHORT COMMUNICATIONS 239