Anaxyrus boreas


Taxonomy [top]

Kingdom Phylum Class Order Family

Scientific Name: Anaxyrus boreas
Species Authority: (Baird & Girard, 1852)
Common Name(s):
English Boreal Toad, Western Toad
Bufo boreas Baird and Girard, 1852

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.
1996 Endangered

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.
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).
Population Trend: Decreasing

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.

Bibliography [top]

1997. Amphibians in Decline: Canadian Studies of a Global Problem. Society for the Study of Amphibians and Reptiles, Herpetological Conservation No. 1.

Behler, J.L. and King, F.W. 1979. The Audubon Society Field Guide to North American Reptiles and Amphibians. New York.

Blackburn, L., Nanjappa, P. and Lannoo, M.J. 2001. An Atlas of the Distribution of U.S. Amphibians. Ball State University, Muncie, IN, USA.

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 Academy of Natural Sciences of Philadelphia: 1791-1795.

Campbell, J.B. and Degenhardt, W.G. 1971. Bufo boreas boreas in New Mexico. Herpetologica: 157-160.

Carey, C. 1993. Hypothesis concerning the causes of the disappearance of boreal toads from the mountains of Colorado. Conservation Biology: 355-362.

Corn, P.S. and Muths, E. 2002. Variable breeding phenology affects the exposure of amphibian embryos to ultraviolet radiation. Ecology: 2958-2963.

Corn, P.S. and Vertucci, F.A. 1992. Descriptive risk assessment of the effects of acidic deposition on Rocky Mountain amphibians. Journal of Herpetology: 361-369.

Corn, P.S., Stolzenburg, W. and Bury, R.B. 1989. Acid precipitation studies in Colorado and Wyoming: interim report of surveys of montane amphibians and water chemistry. U.S. Fish and Wildlife Service Biological Report: 56 pp.

Drost, C.A. and Fellers, G.M. 1996. Collapse of a regional frog fauna in the Yosemite area of the California Sierra Nevada, USA. Conservation Biology: 414-425.

Frost, D.R. 1985. Amphibian Species of the World: A Taxonomic and Geographic Reference. Allen Press and the Association of Systematic Collections, Lawrence, Kansas.

Hailman, J.P. 1984. Bimodal nocturnal activity of the western toad (Bufo boreas) in relation to ambient temperature. Copeia: 283-290.

Hammerson, G.A. 1982. Amphibians and Reptiles in Colorado. Colorado Division of Wildlife, Denver, Denver.

Hammerson, G.A. 1989. A field survey of amphibians in the Rocky Mountains of Colorado, August 1989. Report to the Colorado Division of Wildlife and the Colorado Natural Areas Program.

Hammerson, G.A. 1992. Field surveys of amphibians in the mountains of Colorado, 1991. Report to the Colorado Division of Wildlife and Colorado Field Office of The Nature Conservancy.

Hammerson, G.A. 1999. Amphibians and reptiles in Colorado. Second edition. University Press of Colorado, Boulder.

Herreid, II, C.F. 1963. Range extension of Bufo boreas. Herpetologica: 218-219.

Hodge, R.P. 1976. Amphibians and Reptiles in Alaska, the Yukon and Northwest Territories. Alaska Northwest Publishing Company, Anchorage, Alaska.

IUCN. 2004. 2004 IUCN Red List of Threatened Species. Downloaded on 23 November 2004.

Johnson, P.T.J., Lunde, K.B., Haight, R.W., Bowerman, J. and Blaustein, A.R. 2001. Ribeiroia ondatrae (Trematoda: Digenea) infection induces severe limb malformations in western toads (Bufo boreas). Canadian Journal of Zoology: 370-379.

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

Kiesecker, J.M., Blaustein, A.R. and Miller, C.L. 2001. Transfer of a pathogen from fish to amphibians. Conservation Biology: 1064-1070.

Livo, L.J. and Yeakley, D. 1997. Comparison of current with historical elevational range in the boreal toad, Bufo boreas. Herpetological Review: 143-144.

Muths, E. and Nanjappa, P. 2005. Western Toad. Bufo boreas Baird and Girard, 1852. In: Lannoo, M.J. (ed.), Status and Conservation of U.S. Amphibians. Volume 2: Species Accounts, pp. 64-83. University of California Press, Berkeley, California.

Muths, E., Corn, P.S., Pessier, A.P. and Green, D.E. 2003. Evidence for disease related amphibian decline in Colorado. Biological Conservation: 357-365.

NNHP. 1999. Nevada Natural Heritage Program Database. Carson City, Nevada.

Nussbaum, R.A., Brodie, Jr., E.D. and Storm, R.M. 1983. Amphibians and Reptiles of the Pacific Northwest. University Press of Idaho, Moscow, ID, USA.

Oliver, G.A. 1997. Inventory of sensitive species and ecosystems in Utah. Utah Division of Wildlife Resources, Salt Lake City, Utah.

Olson, D.H. 1989. Predation on breeding western toads (Bufo boreas). Copeia: 391-397.

Olson, D.H. 1992. Ecological susceptibility of high elevation Oregon anuran amphibians to population fluctuations. Abstract, 6th Annual Meeting of the Society for Conservation Biology: p. 102.

Peterson, C.R., Koch, E.D. and Corn, P.S. 1992. Monitoring amphibian populations in Yellowstone and Grand Teton National Parks. Unpublished Report to Univ. Wyo. Natl. Park Serv. Res. Center.

Reichel, J.D. and Flath, D. 1995. Identification of Montana's amphibians and reptiles. Montana Outdoors: 15-34.

Ross, D.A., Esque, T.C., Fridell, R.A. and Hovingh, P. 1995. Historical distribution, current status, and a range extension of Bufo boreas in Utah. Herpetological Review: 187-189.

Samallow, P.B. 1980. Selective mortality and reproduction in a natural population of Bufo boreas. Evolution: 18-39.

Smits, A.W. 1984. Activity patterns and thermal biology of the toad Bufo boreas halophilus. Copeia: 689-696.

Stebbins, R.C. 1985. A Field Guide to Western Reptiles and Amphibians. Second Edition. Houghton Mifflin Company, Boston, Massachusetts.

Welsh, H.H., Jr., Hodgson, G.R. and Lind, A.J. 2005. Ecogeography of the herpetofauna of a northern Californian watershed: linking species patterns to landscape processes. Ecography: 521-536.

Wiedmer, M. and Hodge, R.P. 1996. Geographic distribution: Bufo boreas. Herpetological Review: 148.

Citation: Geoffrey Hammerson, Georgina Santos-Barrera, Erin Muths 2004. Anaxyrus boreas. The IUCN Red List of Threatened Species. Version 2015.2. <>. Downloaded on 27 August 2015.
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