Rarity in North American Passerine Birds

Abstract

Rare species are typically identified by their small geographic range, very low local abundance, or a combination of these two attributes (Rabinowitz 1981; Rabinowitz et al. 1986). However, range size and local abundance are generally not independent of each other, at least when homogeneous taxonomic assemblages are examined across large areas (Bock & Ricklefs 1983; Brown 1984; Arita et al. 1990; Ford 1990; Gaston & Lawton 1990; Lawton 1993; but see Rabinowitz et al. 1986). Direct comparisons between these two parameters are complicated by the fact that range size by definition is a single parameter that pertains to the species as a whole, while local abundance can be measured at many sites throughout the range and, as is well known, often assumes a wide range of values (Hengeveld & Haeck 1982; Rapoport 1982; Brown 1984; Lawton 1993; Mehlman, unpublished data). Therefore, rarity must be examined in the context of the entire spatial distribution of abundance within the range, and it is this distribution that should be examined for correlations