AmphibiaWeb - Anaxyrus boreas
Anaxyrus boreas
Western Toad, Boreal Toad (B. b. boreas), California Toad (B. b. halophilus)
family: Bufonidae

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Conservation Status (definitions)
IUCN (Red List) Status Least Concern (LC)
NatureServe Status Use NatureServe Explorer to see status.
National Status None
Regional Status Declines and or possible extinctions have been reported for populations in the Sierra Nevada, Colorado, New Mexico, Oregon, Utah, and Wyoming (Stebbins and Cohen 1995).
Access Conservation Needs Assessment Report.



View distribution map in BerkeleyMapper.
View Bd and Bsal data (1067 records).

Distinguishing characters include a white or cream dorsal stripe and lack of cranial crest. This species has two known subspecies, Anaxyrus boreas boreas and A. b. halophilus. A. b. boreas is dusky gray or greenish above with warts set in dark blotches, often mixed with a bit of rusty color. Males are usually less blotched with smoother skin and are smaller than females (Stebbins 1985).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Canada, Mexico, United States

U.S. state distribution from AmphibiaWeb's database: Alaska, California, Colorado, Idaho, Montana, New Mexico, Nevada, Oregon, Utah, Washington, Wyoming

Canadian province distribution from AmphibiaWeb's database: Alberta, British Columbia, Yukon


View distribution map in BerkeleyMapper.
View Bd and Bsal data (1067 records).
Populations of A. b. halophilus are found in California, w. Nevada, and n. Baja California. Populations of A. b. boreas are found in southern Alaska, British Columbia, Alberta, Washington, Oregon, Idaho, Montana, Wyoming, Colorado, northern California, Nevada, New Mexico, and Utah. This toad frequents a wide variety of habitats such as, desert streams, grasslands, woodlands, and mountain meadows, and can be found in or near a variety of water bodies (Stebbins 1985).

Life History, Abundance, Activity, and Special Behaviors
This species is an explosive breeder. Females deposit thousands of eggs in long strings, usually in shallow ponds. These toads are nocturnal at low elevations and diurnal at higher elevations. During the winter, A. boreas buries itself in loose soil or uses the burrow of a small mammal (Stebbins 1985). This species tends to walk rather than hop. Both males and females lack an advertisement call (Duellman and Trueb 1986) although they are known to have a release call (Brown and Littlejohn 1971).

Trends and Threats
UV-B radiation has been shown to cause reduced hatching success in Oregon (Blaustein et al. 1994), but not in Colorado, although more investigation is needed (Corn 1998). Synergistic effects between UV-B and an alga, Saprolegnia ferax , have also been shown to cause reduced hatching success in Oregon (Kiesecker and Blaustein 1995). Vertucci and Corn (1993) found that acid precipitation may not be a major cause of the decline of A. b. boreas in Colorado, but more investigation of this problem is needed (Stebbins and Cohen 1995). A. boreas tends to lay its eggs in communal masses, and such communal egg masses have been shown to be highly susceptible to infection with S. ferax (Kiesecker and Blaustein 1997).

In the southern Rocky Mountains, translocation was tried for A. b. boreas. The translocation projects failed; A. b. boreas has been declining in that area for unknown reasons, for some time (Trenham 2001).

Possible reasons for amphibian decline

Habitat modification from deforestation, or logging related activities
Prolonged drought
Habitat fragmentation
Weakened immune capacity
Climate change, increased UVB or increased sensitivity to it, etc.

It has been known to occasionally hybridize with the red-spotted toad (Anaxyrus punctatus) and the Canadian toad (Anaxyrus hemiophrys) (Stebbins 1985).

See other subspecies accounts at B. b. boreas and B. b. halophilus .


Blaustein, A. R., Hoffman, P. D., Hokit, D. G., Kiesecker, J. M., Walls, S. C., and Hays, J. B. (1994). "UV repair and resistance to solar UV-B in amphibian eggs: A link to population declines?" Proceedings of the National Academy of Sciences of the United States of America, 91(5), 1791-1795.

Brown, L. E. and Littlejohn, M. J. (1971). ''Male release call in the Bufo americanus group.'' Evolution in the Genus Bufo. W. F. Blair, eds., University of Texas Press, Austin, 310-323.

Corn, P. S. (1998). "Effects of ultraviolet radiation on boreal toads in Colorado." Ecological Applications, 8, 18-26.

Duellman, W. E., and Trueb, L. (1986). Biology of Amphibians. McGraw-Hill, New York.

Kiesecker, J. M., and Blaustein, A. R. (1995). "Synergism between UV-B radiation and a pathogen magnifies amphibian embryo mortality in nature." Proceedings of the National Academy of Sciences of the United States of America, 92(24), 11049-11052.

Kiesecker, J. M., and Blaustein, A. R. (1997). "Influences of egg laying behavior on pathogenic infection of amphibian eggs." Conservation Biology, 11(1), 214-220.

Stebbins, R. C. (1985). A Field Guide to Western Reptiles and Amphibians. Houghton Mifflin, Boston.

Stebbins, R. C., and Cohen, N. W. (1995). A Natural History of Amphibians. Princeton University Press, Princeton, New Jersey.

Trenham, P. C., and Marsh, D. M. (2001). ''Amphibian translocation programs: reply to Seigel and Dodd.'' Conservation Biology, 16(2), 555-556.

Vertucci, F. A., and Corn, P. S. (1996). "Evaluation of episodic acidification and amphibian declines in the Rocky Mountains." Ecological Applications, 6(2), 449-457.

Originally submitted by: Erica Garcia (first posted 1999-04-07)
Edited by: Vance Vredenburg, Joyce Gross, Kellie Whitaker (2021-01-22)

Species Account Citation: AmphibiaWeb 2021 Anaxyrus boreas: Western Toad <> University of California, Berkeley, CA, USA. Accessed Jan 26, 2022.

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Citation: AmphibiaWeb. 2022. <> University of California, Berkeley, CA, USA. Accessed 26 Jan 2022.

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