Pallid bat (Antrozous pallidus) COSEWIC assessment and status report: chapter 10

Evaluation and Status Recommendation

Antrozous pallidus is afforded legal protection in British Columbia under the Wildlife Act and is currently red-listed by the British Columbia Conservation Data Centre with an S1 provincial ranking, as a species considered "critically imperiled" in the province. It is also classified as a priority 1 species by the South Okanagan Conservation Strategy, as a species native to British Columbia found "only in the South Okanagan" (Chapman et al. 1994). Pallid bats are not considered rare in the Western United States, however, and since 1989, the species has been removed from the Washington State Department of Fish and Wildlife Species of Concern list and enjoys a global ranking of G5 (i.e. "secure"). There is no evidence to suggest that the Canadian population of pallid bats is isolated from the species’ range as a whole and, in 1989, pallid bats were reported just 50 km south of the U.S. border (Grindal et al. 1991). Clearly A. pallidus is not at risk in the majority of its range.

Despite the secure status of this species elsewhere, the pallid bat is facing a number of threats in its limited Canadian range. It now seems virtually certain that a population of A. pallidus is resident in the Okanagan Valley. Capture records date back almost 70 years and recent data refute Balcombe’s (1988) suggestion that the species may be extinct in Canada. Furthermore, there now exists good evidence supporting the existence of resident females and a breeding population in the region. Sexual segregation may put this species at additional risk because it means a wider range of conservation issues need to be addressed in order to protect the habitat requirements of both males and females, though clearly protection of female requirements should be the priority.

A number of factors place pallid bats in Canada at risk. First, all three of the habitat categories required to sustain A. pallidus (i.e. foraging, day roosting and night roosting) are at considerable risk in the Okanagan because of extremely rapid population growth. In the absence of adequate protection in parks and reserves, population growth has already led to considerable habitat destruction because of urban, recreational and agricultural expansion, especially in the low elevations to which pallid bats are confined (Durance 1992, Bailey 1995). Day roosting habitat suitable for maternity colonies, likely the most important of the three habitat types for sustaining a population, faces particular risk because it is generally rare (Robertson 1998; Figure 4), because cliff and rock face roosts, although relatively secure, can be destroyed or disturbed by development and recreation, and because pallid bats have a strong preference for roosting areas in close proximity to foraging sites and vice versa (Robertson 1998). This means that loss of foraging habitat near potential roosts will jeopordize both roosting and foraging opportunities.

Second, and related to habitat loss, Robertson (1998) points out in the guidelines of her habitat evaluation model that 2 of the 28 records for this species were the result of cat kills and a further two bats were found dead or dying from unexplained causes in residential areas. As residential development continues to expand into open sagebrush habitat at lower elevations in the valley, not only will foraging and roosting habitat be disturbed or destroyed, but pallid bats could face increased mortality as a direct result of properties inherent to the residential community. Examples include increased predation by domestic cats (to which pallid bats will be especially sensitive because of their terrestrial foraging strategy), bioaccumulation of domestic garden pesticides, and road kills.

Third, although the effects of intensive pesticide use, common for fruit farming, have not been addressed adequately for this species, it is quite possible that due to increased torpor use, and therefore fat reserve use, in a relatively cool section of their range, pallid bats in Canadan face increased mortality as a result of pesticide bioaccumulation. This hypothesis should be a priority for future research in the Okanagan.

Fourth, and finally, fringe populations are of particular interest to both ecologists and conservationists because it is in marginal habitat that selection pressures can be most pronounced and where diversification and speciation can occur. In addition, conservation efforts must increasingly focus on preserving populations already forced into sub-optimal habitat by human development. Studying the ecology of species living at the limits of their tolerance, then, is important to developing effective conservation strategies (Chapman et al. 1994).

The pallid bat meets COSEWIC criteria for an endangered designation because of its small population size and multiple threats to its habitat. However, because of the reasonably high likelihood of immigration from more stable pallid bat populations in the United States, the most appropriate status would be that of a threatened species in Canada.

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