The number of individuals, or the abundance, of a species\ud in an area is a fundamental ecological parameter and a\ud critical consideration when making management and conservation decisions (Andrewartha and Birch 1954; Krebs\ud 1978; Gaston 1994; Caughley and Gunn 1996). However,\ud unless the scale is very fine or localized (e.g., in a measurable habitat or a forest stand), abundance is not readily determined. At coarse or regional scales for many species, information on commonness and rarity is, at best, limited to a map of their presence or absence from recording units in a specified time frame. Various species data at large scales are increasingly documented in this presence/absence format