The study of habitat use and selection in birds has a long tradition (Grinnell 1917, Kendeigh 1945, Svärdson 1949, Hildén 1965; Block and Brennan 1993). Early habitat-selection theory was characterized by correlative models of habitat characteristics and species abundance (MacArthur and Pianka 1966, Verner et al. 1986, Rosenzweig 1991), which subsequently evolved into models that involved density dependence: the “ideal-free distribution” and “ideal-despotic distribution” models (Fretwell and Lucas 1970, Fretwell 1972). More recently, habitat-selection studies have shown that many factors, such as landscape structure, can influence exactly how”ideal” and “free” animals are while moving through a landscape and selecting habitats (Karr and Freemark 1983, Pulliam and Danielson 1991, Petit and Petit 1996).
Habitat-selection studies have recently assumed a new urgency, partially as a result of the importance of incorporating both habitat and demographic information into conservation planning (Caughley 1994). Nevertheless, ornithologists tend to be inconsistent in their conceptual framework and terminology with regard to (1) what constitutes habitat use versus selection, (2) the behavioral and evolutionary context of their findings, and (3) the order or scale of their study, from microhabitat to geographic range (Johnson 1980, Orians and Wittenberger 1991). The purpose of this review is to address those concerns through a survey of recent literature and highlight areas where improvements or advances can be made in avian habitat ecology.
Three Areas of Concern.—Definitions.—The semantic and empirical distinctions between the terms habitat use and habitat selection are often unclear (Hall et al. 1997). Habitatrefers to a distinctive set of physical environmental factors that a species uses for its survival and reproduction (Block and Brennan 1993). Habitat use refers to the way in which an individual or species uses habitats to meet its life history needs (Block and Brennan 1993). The study of habitat-use patterns describes the actual distribution of individuals across habitat types (Hutto 1985). Habitat selection refers to a hierarchical process of behavioral responses that may result in the disproportionate use of habitats to influence survival and fitness of individuals (Hutto 1985, Block and Brennan 1993). Habitat selection carries a connotation of understanding complex behavioral and environmental processes that habitat use does not; habitat-use patterns are the end result of habitat-selection processes. Nest-site selection is a subset of habitat selection focusing solely on nest sites.