Western toad (Bufo boreas) COSEWIC assessment and status report: chapter 4

Distribution

Bufo boreas occurs from the Rocky Mountains to the Pacific Coast, from sea level to 3660 m (Jones 2000). It is one of the few amphibians that occupy alpine areas. Its eastern range includes western Alberta, western Montana, Colorado, parts of Utah and most of western Nevada. West of the Rocky Mountains, the species occurs from southeast Alaska to Baja California, Mexico (Fig. 2). Within this region, It is absent only from the most arid areas, such as the Columbia Basin in Washington and the Willamette Valley in Oregon (Leonard et al. 1993).

Figure 2. North American distribution of Bufo boreas, indicating the range of the two subspecies, the Boreal toad (B. b. boreas) and the Californiatoad (B. b. halophilus). Reproduced with permission from the North American Center for Amphibian Malformations (original produced by Jeff Jundt and Ralph Tramontano).

Figure 2.  North American distribution of Bufo boreas, indicating the range of the two subspecies, the Boreal toad (B. b. boreas) and the Californiatoad (B. b. halophilus).

Populations appear to be faring well in Canada (Fig. 3). It is found as far north as Yukon as there is a record from Lake Lindeman in the Chilkoot Trail National Historic Site (Mennell 1997) and 13 records from the Liard River Basin, including five separate populations at Meister River, Watson Lake, Toobally Lake, Coal River, and Beaver River (Slough 1999). North-coast records for British Columbia include Sloko Inlet at the south end of Atlin Lake, and Fantail River south of Tagish Lake. The majority of northern records come from valleys that receive early high accumulations of snowfall annually (Cook 1977; Mennell 1997), assuring safe winter hibernation. These permafrost-free valleys may link northern toad populations. It was previously thought that they were isolated by an over-wintering dependence on hotsprings (Cook 1977).

Figure 3. Distribution of Bufo boreas within Canada. Map plotted by Arnold Moy.

Figure 3.  Distribution of Bufo boreas withinCanada. Map plotted by Arnold Moy.

Bufo boreas is the only amphibian evidently native to the Queen Charlotte Islands of British Columbia (Green and Campbell 1984). It is absent from the northeast corner of the province, in the Taiga Plains Ecoprovince and in the north-central portion of the Northern Boreal Mountains Ecoprovince, but common historically (Hollister 1912, Williams 1933, Wade 1960, Green 1975) and currently (Poll et al. 1984, Kinsey and Law 1998, Hengeveld 2000) throughout the Interior. Tadpoles and metamorphosed individuals are seen frequently throughout the midcoast (P. Friele, pers. com.). Metamorphs have been relatively abundant as far south as Strathcona Park (K. Ovaska, pers. com.) on Vancouver Island, and the Elaho watershed and Garibaldi Mountains north of Squamish (Dupuis, pers. obs.). The species may have declined, however, on southern and central Vancouver Island, and in the Lower Mainland of British Columbia, where recent records are scarce (e.g., Haycock and Knopp 1998, Dupuis 1998, Davis 2000, Beasley et al. 2000, Materi and Blood 2000). Bufo boreas is common in Alberta, from the Lac la Biche area in the central east (Eaton et al. 1999) to the BC border. Only two sightings of toads have been reported north of Slave Lake (Russell and Bauer 1993), which may be a reflection of the inaccessibility of northern regions rather than of toad densities.

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