Pallid bat (Antrozous pallidus) COSEWIC assessment and status report: chapter 8

Biology

In addition to roosting ecology, one important aspect of A. pallidus biology has been well investigated since the original COSEWIC status report for this species was prepared in 1988. Particularly relevant to northern populations of the species is the work done, once again by Lewis (1993) in Oregon, addressing the effects of climatic variation on aspects of reproduction. Prior to this research it was unknown whether a ground foraging bat faced the same energetic trade-offs as aerial insectivores with respect to the use of heterothermy (i.e. torpor) during pregnancy and lactation. By comparing pallid bats captured in a relatively cool spring and those captured during a normal spring, Lewis (1993) found that during a cooler year females exhibited a delay of nearly a month in parturition dates, less synchrony of parturition, lower body mass when lactating and a higher percentage of non-reproductivity. This has important implications for the stability of a Canadian population of A. pallidus, where bats very likely face regular exposure to cold temperatures near the limits of their tolerance.

Relatively low temperatures and inter-season climatic variation may account for the low and sporadic capture rate of reproductively active, and female pallid bats in the Okanagan. Because bats, generally, are very long lived mammals, however, inter-year variation in reproductive success does not necessarily preclude a stable breeding population. A female bat who fails to reproduce in a cool year may still have a relatively high probability of surviving to reproduce successfully in a warmer year.

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