Pallid bat (Antrozous pallidus) COSEWIC assessment and status report: chapter 4

Distribution

No evidence has been presented after 1988 to suggest that A. pallidus range in Canada or the United States has changed since that time, although field study in the Okanagan Valley by Collard and Grindal, Chapman and McGuiness, and Barclay and his students after 1988 provides convincing evidence that a resident population exists in south-central B.C. No evidence is available to suggest that these animals are isolated from pallid bat populations in Washington State to the south and the remainder of the species’ North American range, which is presented in Figure 1.

Figure 1. North American distribution of the pallid bat (Antrozous pallidus) (from Grindal et al. 1991).

North American distribution of the pallid bat (Antrozous pallidus) (from Grindal et al. 1991)

Locations of recorded occurrences of A. pallidus are provided in Figure 2. A. pallidus captures or recovered specimens have been confirmed only 28 times since the species was first reported in the southern Okanagan Valley in 1931. The size of the distributional area in Canada is difficult to estimate because some areas have received more survey attention than others, but is likely between 150 and 500 km².

Figure 2. Locations of recorded occurences of Antrozous pallidus in Canada.  Each white dot represents a single captured female bat and each grey dot a single captured male. The heavy, solid black line represents the boundary of the Inkaneep Indian Reserve. Dots are placed as closely as possible to capture sites but are not precisely placed because of limited space. Re-captures are included as individual dots (modified from Chapman et al. 1994).

 Locations of recorded occurences of Antrozous pallidus in Canada

The majority of pallid bat captures have occurred between Vaseux Lake and Osoyoos, especially on the Inkaneep Indian Reserve which may be due to the fact that, traditionally, the Reserve has been subject to less development than the Okanagan region as a whole (Chapman et al. 1994), though no direct evidence exists to support this hypothesis. Based on compilations of visual observation, directive calls (which are audible to human observers and serve as social contact calls between individuals (Brown 1976)), and captures (6 reproductively active males and 1 non-reproductive male) in 1991, Chapman et al. (1994) estimated that a minimum of 12 animals were resident on the Inkaneep Reserve. Interestingly, their surveys of the neighbouring Similkameen River valley for spotted bats (Euderma maculatum) yielded no captures, sightings, or directive call counts for A. pallidus, although this work is likely insufficient to verify, conclusively, the absence of pallid bats from the Similkameen Valley (Brigham, personal communication).  The absence of high quality foraging and breeding area in the Similkameen, as determined by a recent B.C. environment habitat evaluation model (Robertson 1998; Figure 3; and see below), however, may be a contributing factor.

Figure 3. Habitat suitability map for Antrozous pallidus in the south Okanagan. (Robertson 1998).

 Habitat suitability map for Antrozous pallidus in the south Okanagan

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