Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Amphibia Anura Bufonidae

Scientific Name: Anaxyrus boreas
Species Authority: (Baird & Girard, 1852)
Common Name(s):
English Western Toad, Boreal Toad
Bufo boreas Baird and Girard, 1852
Taxonomic Source(s): Frost, D.R. 2014. Amphibian Species of the World: an Online Reference. Version 6 (27 January 2014). New York, USA. Available at: (Accessed: 27 January 2014).

Assessment Information [top]

Red List Category & Criteria: Near Threatened ver 3.1
Year Published: 2004
Date Assessed: 2004-04-30
Needs updating
Assessor(s): Geoffrey Hammerson, Georgina Santos-Barrera, Erin Muths
Reviewer(s): Global Amphibian Assessment Coordinating Team (Simon Stuart, Janice Chanson, Neil Cox and Bruce Young)
Listed as Near Threatened because this species is probably in significant decline (but probably at a rate of less than 30% over ten years) because of disease (including chytridiomycosis), thus making the species close to qualifying for Vulnerable.
Previously published Red List assessments:
1996 Endangered (EN)

Geographic Range [top]

Range Description: This species occurs along the Pacific Coast of North America from southern Alaska (Wiedmer and Hodge 1996) to Baja California, and ranges eastward to the Rocky Mountains in west-central Alberta, Montana, Wyoming, Utah (Ross et al. 1995), Colorado (Hammerson 1999), and (formerly) northern New Mexico (Degenhardt, Painter and Price 1996). It is absent from most of the desert south-west (Stebbins 1985b). Its altitudinal range extends from sea level to at least 3,640m asl.
Countries occurrence:
Canada; Mexico; United States
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: The total adult population size of the species is unknown but is likely to exceed 100,000. It is still common in much of its range. The Rocky Mountain populations in Colorado and Wyoming have undergone a drastic decline since the 1970s (Corn, Stolzenburg and Bury 1989; Hammerson 1989, 1992, 1999; Carey 1993; Muths et al. 2003). It has also declined greatly in the Yosemite area of the Sierra Nevada, California (Drost and Fellers 1996). It is apparently undergoing localized declines in Yellowstone National Park (Peterson, Koch and Corn 1992), Montana (Reichel and Flath 1995), and elsewhere (Olson 1989).
Current Population Trend: Decreasing
Additional data:
Population severely fragmented: No

Habitat and Ecology [top]

Habitat and Ecology: This species is found in a wide variety of habitats including desert springs and streams, meadows and woodlands and mountain wetlands. It is also known from around ponds, lakes, reservoirs, and slow-moving rivers and streams. It digs its own burrow in loose soil or uses those of small mammals, or shelters under logs or rocks. The eggs and larvae develop in shallow areas of ponds, lakes, or reservoirs, or in pools of slow-moving streams.
Systems: Terrestrial; Freshwater

Threats [top]

Major Threat(s): The extent of threat across the species' range is not known with certainty. The decline in the Southern Rocky Mountains is not due to acidification of breeding habitats (Corn and Vertucci 1992). Carey (1993) hypothesized that some environmental factor or synergistic effects of more than one factor might stress the toads, causing suppression of the immune system or indirectly causing immunosuppression by causing elevated secretion of adrenal cortical hormones; immunosuppression, coupled with the apparent effect of cold body temperatures on the ability of the immune system to fight disease, might lead to infection by Aeromonas hydrophila bacteria (which causes "red-leg") or other infectious agents and subsequently to death of individuals and the extirpation of populations. Die-offs in the southern Rockies have been associated with chytrid fungus infections (Muths et al. 2003). Eggs are highly susceptible to the pathogenic fungus Saprolegnia ferax, which might be introduced during fish stocking (Kiesecker and Blaustein 1997). Another possibility is that declines are related to the sensitivity of eggs to increased levels of ultraviolet radiation (Blaustein et al. 1994), but see Corn and Muths (2002) for an alternative viewpoint. In the Cascade Range of Oregon, persistent predation of adults by ravens during the toad breeding season appears to have contributed significantly to some population declines (Olson 1992). Possibly significant predation by birds has also been observed in Colorado and Idaho. The decline might be related, at least in part, to habitat destruction and degradation, water retention projects, predation by, and competition with, native and non-native species, fishery management activities, or other factors, but these factors have not been adequately assessed.

Conservation Actions [top]

Conservation Actions: This species occurs in many national parks, wildlife refuges, and wilderness areas in the US where habitat destruction is not a major threat. In Mexico, it is found within Parque Nacional Sierra de San Pedro Martir. It is listed as an endangered species in the state of Colorado and is warranted but precluded from US federal endangered species status.

Citation: Geoffrey Hammerson, Georgina Santos-Barrera, Erin Muths. 2004. Anaxyrus boreas. The IUCN Red List of Threatened Species 2004: e.T3179A9654897. . Downloaded on 09 October 2015.
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