Factors Associated With Variation in Home-Range Size of Appalachian Ruffed Grouse (Bonasa Umbellus)

Abstract

Abstract From 1996 to 2001, researchers at 10 Appalachian study sites collected radiotracking data sufficient to delineate 1,054 seasonal home ranges of Ruffed Grouse (Bonasa umbellus; hereafter “grouse”). Using information-theoretic model selection and paired comparison of home ranges from individual grouse, we evaluated individual, local, and landscape factors hypothesized to affect grouse home-range size. Females and juvenile males occupied home ranges that averaged >2× larger than those of adult males, and home ranges of females averaged 2.6× larger during successful breeding seasons than during years of reproductive failure. Clearcuts and forest roads are considered high-quality covers, and both were more prevalent in smaller home ranges. Several factors operating at a regional and landscape scale were also important. Previous studies have reported that southern grouse use relatively large home ranges, and we observed a continuous decline in home-range size with increasing latitude across the 710-km range spanned by our study sites. Home-range size of males, particularly juvenile males, was positively related to an index of population density. Given the species' “dispersed lekking” mating system, we interpret this as evidence of competition for preferred display sites. As has been reported for other game birds, all sex and age classes of grouse used smaller home ranges following closure of sites to hunting. Grouse inhabiting oak-hickory forests used larger home ranges than conspecifics in mixed mesophytic forests, and other factors interacted with forest type. In oak-hickory forests, female home-range size was inversely related to use of mesic bottomlands, which support important forage plants, and home ranges of adult grouse increased 2.5× following poor hard-mast crops. By contrast, home ranges of grouse inhabiting mixed mesophytic forests were unrelated to use of bottomlands, and the influence of hard mast was reduced. This is in line with the view that in Appalachian oak-hickory forests, grouse are under strong nutritional constraint. However, this constraint is reduced in mixed mesophytic forests, likely because of the presence of high-quality alternative foods (e.g., cherry [Prunus spp.] and birch [Betula spp.]). Facteurs associés à une variation de la taille du domaine vital de Bonasa umbellus dans les Appalaches