Anaxyrus baxteri


Taxonomy [top]

Kingdom Phylum Class Order Family

Scientific Name: Anaxyrus baxteri
Species Authority: (Porter, 1964)
Common Name(s):
English Baxter's Toad, Wyoming Toad
Bufo baxteri Porter, 1964
Bufo hemiophrys Cope, 1886

Assessment Information [top]

Red List Category & Criteria: Extinct in the Wild ver 3.1
Year Published: 2004
Date Assessed: 2004-04-30
Needs updating
Assessor(s): Geoffrey Hammerson
Reviewer(s): Global Amphibian Assessment Coordinating Team (Simon Stuart, Janice Chanson, Neil Cox and Bruce Young)
List as Extinct in the Wild because no self-sustaining population exists in the wild, but the species survives in captivity.

Geographic Range [top]

Range Description:This species is restricted to the Laramie Basin, Wyoming, USA. The historical range extent was approximately 2,330kmĀ² (USFWS data). As of 2002, it was extant only at Mortenson Lake National Wildlife Refuge, which encompasses four impoundments: Mortenson, Garber, Gibbs, and Soda lakes; the refuge is closed to the public (USFWS 2002e). The extant occurrence probably would be extirpated without recent annual releases of captive-reared toadlets. Populations at former re-introduction sites (Lake George on the Hutton Lake National Wildlife Refuge, and Rush Lake) have been lost due to drought (USFWS 2002e).
Regionally extinct:
United States
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population: This species was common in the 1950s, but underwent a large decline in the 1960s and 1970s; it was thought to be extinct in the wild in the mid-1980s, but was found again at Mortenson Lake in 1987 and captive propagation began in the mid-1990s using toads from Mortenson Lake (USFWS 2002e). At Mortenson Lake, there has been no natural reproduction by wild toads since 1991; the population is maintained through release of captive-reared young (Parker, Anderson and Lindzey 2000). In June 2002, a survey at Mortenson Lake NWR yielded 124 yearlings and 4 adults (USFWS 2002e). Limited natural reproduction and recruitment of a few metamorphosed juveniles occurred in 2002 (USFWS 2002e). Despite releases of captive-reared individuals, the population at Mortenson Lake NWR appears to be declining (USFWS 2002e).
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: Historically, it is associated with floodplain ponds along the Big and Little Laramie Rivers; use of lakes might have been limited due to saline conditions; irrigation might have flushed out the lakes and made them more suitable for toads (G. Baxter pers. comm.). Currently, it occurs in the vicinity of lakes and adjacent meadows. It uses rodent burrows for shelter. Eggs and larvae develop in shallow water.
Systems: Terrestrial; Freshwater

Threats [top]

Major Threat(s): Mortenson Lake, site of the only known extant population, is infected with the amphibian chytrid fungus (USFWS 2002e). This fungus has been implicated in declines and extinctions of amphibian species worldwide. Retrospective analysis shows that the fungus has been present at Mortenson Lake since at least 1989. In addition, chytridiomycosis is the most commonly seen disease in the captive population. Predation, pesticide use, irrigation practices, and lack of genetic diversity might also limit the abundance of Wyoming Toads in the Laramie Basin. The cause of the original decline remains unknown but might be associated with the invasion of chytrid into the area (USFWS 2002e). Mortenson Lake recently has become more saline (and less suitable for toads) as a result of drought-related increases in evaporation (USFWS 2002e). Salt-cedar was found (and removed) at Hutton Lake NWR in 2002. This plant has the potential to reduce habitat suitability (USFWS 2002e). For the past several years, beginning in late summer, adults with bacterial and fungal infections have been found moribund or dead (Taylor et al. 1999). Predators, probably mustelids, killed several radio-tagged individuals in 1998 (Parker, Anderson and Lindzey 2000).

Conservation Actions [top]

Conservation Actions: It occurs in Mortenson Lake National Wildlife Refuge, where a recovery programme, using captive-bred animals and re-introductions, is being implemented. TNC recently acquired a 1,800-acre tract at Mortensen Lake and has arranged a conservation easement with an adjacent landowner. Lake George also is a toad refuge. The success of the recovery programme probably depends on finding some way to combat chytridiomycosis in the wild.

Bibliography [top]

Baxter, G.T. and Stone, M.D. 1980. Amphibians and Reptiles of Wyoming. Wyoming Game and Fish Department.

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

Collins, J.T. 1991. Viewpoint: a new taxonomic arrangement for some North American amphibians and reptiles. SSAR Herpetological Review: 42-43.

Dickerson, K. 1999. Pesticides and the Wyoming toad. Endangered Species Bulletin: 20-21.

Dowling, H.G. 1993. Viewpoint: a reply to Collins (1991, 1992). Herpetological Review: 11-13.

Green, D.M. 1983. Allozyme variation through a clinal hybrid zone between the toads Bufo americanus and B. hemiophrys in southeastern Manitoba. Herpetologica: 28-40.

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

Lewis, D.L., Baxter, G.T., Johnson, K.M. and Stone, M.D. 1985. Possible extinction of the Wyoming toad, Bufo hemiphrys baxteriI. Journal of Herpetology: 166-168.

Matthews, J.R. and Moseley, C.J. (eds). 1990. The Official World Wildlife Fund Guide to Endangered Species of North America. Volume 2. Birds, Reptiles, Amphibians, Fishes, Mussels, Crustaceans, Snails, Insects, and Srachnids. Beacham Publications, Inc., Washington, D.C.

Parker, J., Anderson, S.H. and Lindzey, F.J. 2000. Natural history notes. Bufo baxteri. Herpetological Review: 167-168.

Smith, H.M., Chiszar, D., Collins, J.T. and van Breukelen, F. 1998. The taxonomic status of the Wyoming toad, Bufo baxteri Porter. Contemporary Herpetology.

Spencer, B. 1999. The Wyoming toad SSP. Endangered Species Bulletin: 18-19.

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

Taylor, S.K., Williams, E.S., Thorne, E.T., Mills, K.W., Withers, D.I. and Pier, A.C. 1999. Causes of mortality of the Wyoming toad. Journal of Wildlife Diseases: 49-57.

U.S. Fish and Wildlife Service. 1990. Endangered and threatened species recovery program: report to Congress.

U.S. Fish and Wildlife Service. 2002. Wyoming Field Office Annual Wyoming Toad Report FY 02..

Citation: Geoffrey Hammerson 2004. Anaxyrus baxteri. In: The IUCN Red List of Threatened Species. Version 2015.2. <>. Downloaded on 29 August 2015.
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