Factors Affecting Interspecies Variation in Home-range Size of Raptors

Considerable work has been devoted to examining factors that affect interspecies variation in home-range size. Home ranges for most vertebrates increase with body mass and decrease with increased habitat productivity (e.g. McNab 1963, Schoener 1968, Harestad and Bunnell 1979, Lindstedt et al. 1986). Large species have high energetic requirements and presumably must occupy large home ranges to obtain sufficient food, but even small species occupy relatively large home ranges when the availability of food is low. Interspecific variation in home-range size also has been attributed to differences in age and sex (Harestad and Bunnell 1979, Schoener and Schoener 1982), dominance status (Schoener and Schoener 1982), and trophic status (McNab 1963, Schoener 1968). For example, McNab (1963) showed that mammalian “hunters” have larger home ranges than similar-sized “croppers” and suggested that this difference was due to less biomass of food per unit area being available at higher trophic levels. Raptors provide valuable insights into the factors that affect an animal's home-range size because they use many different hunting tactics and take many different kinds of prey (Snyder and Wiley 1976, Marti et al. 1993, Korpimäki and Marti 1995). Newton (1979:63) has shown that home-range size of raptors increases with body mass, and Schoener (1968) has shown that predatory birds have larger home ranges than similar-sized nonpredatory birds. Here, I extend Newton's and Schoener's analyses by asking the question: Does the way in which a raptor exploits its prey base influence the size of its home range?