Fringed bat COSEWIC assessment and status report: chapter 7
Population Sizes and Trends
There are no population estimates for the Canadian population and no data exist to assess population trends. Because the ultrasonic echolocation calls of most Canadian Myotis species can not be reliably discriminated to species with most bat detectors, inventories of the Fringed Bat are restricted to captures in mist nets or harp traps. In comparison to the 6 other Myotis species found within its range in Canada, the Fringed Bat is rarely captured in surveys with mist nets and harp traps. Of 420 bats captured at 22 sites in the southern Okanagan Valley by Fenton et al. (1979), only 6 were Fringed Bats. Of 528 bats captured by Collard et al. (1990) in the southern Okanagan and Similkameen valleys, 38 were Fringed Bats with 34 of these captures from a single night roost. In a survey of 64 sites throughout the grasslands of the British Columbia interior, Holroyd et al. captured 484 bats--only 6 were Fringed Bats. To what extent the few captures can be attributed to rarity or simply this species’ ability to avoid capture is unknown.
Although maternity colonies of this bat in buildings can be large with more than a 1,000 individuals, the two maternity colonies found in Canada were small. Maslin (1938) estimated the colony in the attic of a house near Vernon at 30 to 40 animals including young; Sarell and Haney (2000) estimated the colony in the attic of a house at Trout Creek to be about 50 animals including young. There are no data on population trends for these two colonies. According to Sarell (pers. comm.), the colony at Trout Creek has not been censused since it was first discovered in the summer of 2000.
Although the population status of the Fringed Bat in Washington State is unknown, this species has been detected in Okanogan County near the British Columbia border (Sarell and McGuiness 1993; Johnson and Cassidy 1997). Trans-border movements are likely.
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