Spotted bat (Euderma maculatum) COSEWIC assessment and status report: chapter 4

Distribution

Global range

The Spotted Bat ranges from central Mexico and the western United States (Arizona, New Mexico, Nevada, Texas, California, Oregon, Utah, Colorado, Wyoming, Montana, Idaho, Washington) to southern British Columbia (Figure 2). Throughout its range, this bat has a patchy distribution (Fenton et al. 1987; Pierson and Rainey 1998).

Canadian range

In Canada, this bat is restricted to southern British Columbia where it is generally found below 900 m in valleys of the dry interior grasslands (Nagorsen and Brigham 1993). Because the Spotted Bat can be detected and identified by its audible echolocation calls, it is one of the few Canadian bat species that can be inventoried without relying on captures (Fenton et al. 1987). Although the Spotted Bat has probably inhabited Canada since the early Holocene, its echolocation calls were only first detected in 1979; identification was verified from a museum specimen (RBCM 10799) collected in 1980 (Woodward et al. 1981). Subsequent surveys (Collard et al. 1990; Roberts and Roberts 1992, 1993; Holroyd et al. 1994; Sarell and Haney 2000) and incidental observations from naturalists demonstrate that Spotted Bats inhabit the Okanagan, Similkameen, Thompson, Fraser and Chilcotin River valleys (Figure 3). Northernmost occurrences are at Macalister north of Williams Lake in the Fraser River and Bull Canyon in the Chilcotin River.

Figure 2. Global range of the Spotted Bat (Euderma maculatum).

Figure 2.  Global range of the Spotted Bat (Euderma maculatum)

The 80 distributional records (roosting and foraging records) of the Spotted Bat in Canada represent about 40 element occurrences[1]. Although the distributional records (Figure 3) are clustered into three regions (Cariboo-Fraser, Thompson, southern Okanagan-Similkameen) suggesting the existence of three subpopulations, this disjunct pattern is probably an artifact of sampling.  Little inventory work has been done in the north Okanagan valley or the Fraser River valley between Lillooet and Churn Creek.

Figure 3. Canadian range of the Spotted Bat (Euderma maculatum).

Figure 3.  Canadian range of the Spotted Bat (Euderma maculatum)

The various inventories done in Canada have not systematically recorded the presence-absence of this bat at sites. For example, in the comprehensive survey done by Sarell and Haney (2000) in the southern Okanagan and Similkameen, only sites with high habitat potential were surveyed (Sarell pers. comm.) and no attempt was made to document sites where the Spotted Bat was not detected. Nevertheless, given the irregular distribution of suitable cliffs and rock outcrops, locally the Spotted Bat appears to be discontinuous in its distribution.

Historical distributional changes cannot be assessed because the Spotted Bat's Canadian range has only been delimited over the past few decades. The area of occupancy is unknown; the extent of occurrence in Canada is about 10,590 km². This represents less than 5% of the species' global range.

[1] An element occurrence for small bats is defined by the Heritage Ranking System as sites occupied historically or at present that are separated by 10 km or more.

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