Pallid bat (Antrozous pallidus) COSEWIC assessment and status report: chapter 3

Introduction

The pallid bat (Antrozous pallidus, Chiroptera: Vespertilionidae) is found throughout arid and semi-arid regions of western North America from Mexico to the Okanagan Valley in south-central British Columbia. This distinctive species is a large bat by North American standards, and Canada’s largest, at 12.0 - 24.3 g with a 310 - 370 mm wingspan (Nagorsen and Brigham 1993). It is characterized by large ear and eyes, and short pale fur which fades from yellowish brown dorsally to a cream colour ventrally. In contrast to most North American bats, A. pallidus typically gleans arthropods from surfaces and often travels to a night roost before feeding, where unpalatable parts can be removed. This species feeds on a range of arthropods, including scorpions (Edwards 1974), beetles and moths (Hermanson and O’Shea 1983) but may consume non-arthropods and has even been reported taking a 7-10 gram pocketmouse (Perognathus flavus) (Bell 1982).

Balcombe (1988) suggested a COSEWIC designation of vulnerableFootnote1 for A. pallidus based on its sporadic occurence in Canada, which he attributed primarily to the fact that the Okanagan Valley represents the northern range boundary for this species, but also to possible anthropogenic limitations. Balcombe (1988) suggested agriculture and logging, particularly, could put an Okanagan population of A. pallidus at direct risk due to habitat disturbance, and indirect risk due to bio-accumulation of the pesticides widely used in fruit farming, the most common type of agriculture in the region. Logging, however, may have little impact on pallid bats because it occurs at relatively high elevations, above the 300-490 m within which this species has been observed in B.C. (Nagorsen and Brigham 1993, Brigham, personal communication).

Prior to 1988 A. pallidus had been recorded from the southern Okanagan Valley only six times (e.g. Racey 1933, Anderson 1946, Fenton 1980) and a lack of success locating it in 1986 (Fenton et al. 1987) led Balcombe (1988) to suggest the possibility that previous accounts may have involved stray representatives of a population resident south of the Canada-U.S. border. Compounding uncertainty regarding a Canadian population of the species was the fact that even in the southwestern United States, where A. pallidus is abundant, population sizes were poorly estimated as of 1988.

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