Keen's long-eared bat (Myotis keenii) COSEWIC assessment and status report: chapter 7

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Population Sizes and Trends

No estimates exist for the total Canadian population and nothing is known about their overall population trend. The paucity of records, however, indicates that this species is not commonly encountered, and may only occur in low densities. This is supported by the results of a 1991 survey specifically designed to determine the distribution and abundance of M. keenii in British Columbia (Firman et al., 1993). Despite mist netting and trapping bats for 76 nights at 53 locations, the authors only captured 38 long-eared bats at five different locations (Figure 4). All M. keenii (29 individuals) were captured at Gandl K’in Gwaayaay. Two of the remaining 9 were identified as M. evotis, while identification of the other 7 could not be determined to the species level.

The only other indication for population trends for this species comes from recent studies of the Gandl K’in Gwaayaay maternity colony. In the initial survey of this colony, Firman et al. (1993) estimated that about 140 bats were present in early August 1991, of which they estimated that one half were M. keenii. In subsequent studies, using emergence counts conducted in June and a ratio of the relative numbers of each species captured, Burles (2001) calculated that the ratio was more likely 1/3 M. keenii/2/3 M. lucifugus, and estimated that 39 - 41 adult female M. keenii and 71 - 86 M. lucifugus used the roosts during 1998, 1999 and 2000 (Table 3). Burles (2001) found that the total number of bats using the roosts increased during late July as a result of young beginning to fledge and non-reproductive bats frequenting the roosts. By early August 1999, for example, the total number counted had risen to at least 149, which is similar to the number estimated by Firman et al. (1993). These results suggest that the number of female M. keenii using the Gandl K’in Gwaayaay roosts remained quite stable during the period 1998 – 2000, and probably did not vary much between 1991 and 2000.

Emergence counts conducted during 2002 indicated that fewer bats were using the roosts at Gandl K’in Gwaayaay, and, based on the relative numbers of the two species seen emerging (Table 3), this decline appeared to be due to fewer M. keenii being present (Burles, unpublished data). As Burles (2001) pointed out, however, emergence counts at this particular colony can be quite variable because not all females use the maternity roosts every day, and not all females emerge to forage every evening. Multiple emergence counts are thus required in order to sample on an evening when most, if not all, bats are present and emerge. It remains to be seen then, whether the 2002 counts are an accurate reflection of the number of M. keenii using the maternity roosts.