Anaxyrus canorus


Taxonomy [top]

Kingdom Phylum Class Order Family

Scientific Name: Anaxyrus canorus
Species Authority: (Camp, 1916)
Common Name(s):
English Yosemite Park Toad, Yosemite Toad
Bufo canorus Camp, 1916
Taxonomic Notes: Molecular data suggest that Anaxyrus exsul is possibly conspecific with this species.

Assessment Information [top]

Red List Category & Criteria: Endangered A2ae ver 3.1
Year Published: 2004
Date Assessed: 2004-04-30
Assessor(s): Geoffrey Hammerson, Rob Grasso, Carlos Davidson
Reviewer(s): Global Amphibian Assessment Coordinating Team (Simon Stuart, Janice Chanson, Neil Cox and Bruce Young)
Listed as Endangered because of a serious population decline, estimated to be more than 50% over the last ten years, inferred from observed reduction in the number of mature individuals, possibly due to disease.
1996 Endangered

Geographic Range [top]

Range Description:This species is endemic to the state of California, USA. It is found only in the high sierra from the Blue Lakes region north of Ebbets Pass (Alpine County) south to Spanish Mountain area (Fresno County), and is found at elevations of 1,460-3,630m asl.
United States
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population: The total adult population size is unknown but is likely to be at least a few thousand. Declines, some in seemingly pristine environments, occurred in the eastern Sierra Nevada between the early 1970s and early 1990s (Kagarise Sherman and Morton 1993). Although still distributed over most of its original range, and many populations have active breeding and recruitment (Shaffer et al. 2000), the species has declined or disappeared from more than 50% of the sites from which it has been recorded (Jennings and Hayes 1994; Drost and Fellers 1996). USFWS (2000) reviewed additional evidence of declines in distribution and abundance.
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: It inhabits wet mountain meadows and borders of forests, and obtains shelter in rodent burrows as well as in dense vegetation. This species breeds in shallow edges of snowmelt pools and ponds or along edges of lakes and slow-moving streams. Some breeding sites dry up before larvae metamorphose. Females may breed every other year or once every three years. It persists in meadow habitats degraded by cattle as well as in lakes stocked with non-native trout.
Systems: Terrestrial; Freshwater

Threats [top]

Major Threat(s): Leading hypotheses for the declines are disease (chytridiomycosis), airborne contaminants, and livestock grazing. An examination of preserved specimens from a 1970 die-off found multiple pathogens, but no single pathogen was present in more than 25% of the specimens, suggesting that the animals suffered from suppressed immune systems (Green and Kagarise Sherman 2001). Davidson, Shaffer and Jennings (2002) found a weak pattern between declines at sites and amount of agricultural land upwind (suggesting that windborne agrochemicals may have contributed to declines). Livestock grazing may have detrimental impacts on Yosemite Toads through trampling, alteration of meadow habitat, and possible lowered water quality (D. Martin pers. comm.). Other factors that may have contributed to declines are the 1980s California drought, and predation by introduced trout. Ultraviolet radiation is not suspected to be a major contributor to declines based on fieldwork by Sadinski (pers. comm.).

Conservation Actions [top]

Conservation Actions: Most of the habitat of this species is confined within protected areas including: Yosemite National Park, Kings Canyon National Park, wilderness areas of Eldorado, Inyo, Stanislaus, and Sierra National Forest, with the highest number of populations recorded in Sierra National Forest followed by Stanislaus National Forest. Off-highway vehicle use, pack stock and cattle grazing still occur in National Forests, as well as protected wilderness areas; only pack stock use continues in Yosemite National Park and Kings Canyon National Park. Because declines have occurred in pristine areas in parks, no occurrences can be regarded as adequately protected. This species has been federally petitioned for listing under the Endangered Species Act in March 2000 by the Pacific Rivers Council and Centre for Biological Diversity. In December 2002 the US Fish and Wildlife Service published a decision in the Federal Register that placed the toad on the "warranted-but-precluded" list due to higher priority listings. Further taxonomic work is required to determine the status of this species relative to B. exsul.

Bibliography [top]

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.

Bradford, D.F., Swanson, C. and Gordon, M.S. 1992. Effects of low pH and aluminum on two declining species of amphibians in the Sierra Nevada, California. Journal of Herpetology: 369-377.

Camp, C.L. 1916. Description of Bufo canorus, A New Toad from the Yosemite National Park. University of California Publications in Zoology: 59-62.

Cunningham, J.D. 1963. Additional observations on the ecology of the Yosemite toad, Bufo canorus. Herpetologica: 56-61.

Davidson, C., Shaffer, H.B. and Jennings, M.R. 2002. Spatial tests of the pesticide drift, habitat destruction, UB-B, and climate-change hypotheses for California amphibian declines. Conservation Biology: 1588-1601.

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.

Green, D.E. and Kagarise Sherman, C. 2001. Diagnostic histological findings in Yosemite toads (Bufo canorus) from a die-off in the 1970s. Journal of Herpetology: 92-103.

Grinnel, J. and Storer, T.I. 1924. Animal Life in the Yosemite. Univ. of California, Berkeley, California.

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

Jennings, M.R. and Hayes, M.P. 1994. Amphibian and reptile species of special concern in California. Final Report submitted to the California Department of Fish and Game, Inland Fisheries Division. Contract No. 8023.

Kagarise Sherman, C. and Morton, M.L. 1993. Population declines of Yosemite toads in the eastern Sierra Nevada of California. Journal of Herpetology: 186-198.

Karlstrom, E.L. 1962. The toad genus Bufo in the Sierra Nevada of California. University of California Publications in Zoology: 1-104.

Karlstrom, E.L. 1973. Bufo canorus. Catalogue of American Amphibians and Reptiles: 1-2.

Karlstrom, E.L. and Livezy, R.L. 1955. The eggs and larvae of the Yosemite toad Bufo canorus Camp. Herpetologica: 221-227.

Martin, D.L. 1991. Population Status of the Yosemite Toad, Bufo canorus, A Progress Report. Yosemite Association, California.

Mullally, D.P. 1953. Observations on the ecology of the toad Bufo canorus. Copeia: 182-183.

Shaffer, H.B., Fellers, G.M., Magee, A. and Voss, S.R. 2000. The genetics of amphibian declines: population substructure and molecular differentiation in the yosemite toad, Bufo canorus (Anura, Bufonidae) based on single-strand conformation polymorphism analysis (SSCP) and mitochondrial DNA sequence data. Molecuar Ecology: 245-257.

Sherman, C.K. 1980. A comparison of the natural history and mating system of two anurans: yosemite toads (Bufo canorus) and black toads (Bufo exsul). Ph.D. Dissertation, University of Michigan, Ann Arbor, Michigan.

Stebbins, R.C. 1972. California Amphibians and Reptiles. University of California Press, Berkeley, California.

Stebbins, R.C. 1985. A Field Guide to the Reptiles and Amphibians of Eastern North America. Houghton Mifflin Company, Boston, Massachusetts.

Stebbins, R.C. 2003. A Field Guide to Western Reptiles and Amphibians, Third Edition. Houghton Mifflin Company, Boston, Massachusetts.

U.S. Fish and Wildlife Service. 2000. 90-day finding on a petition to list the Yosemite toad as endangered. Federal Register: 60607-6060.

Citation: Geoffrey Hammerson, Rob Grasso, Carlos Davidson 2004. Anaxyrus canorus. In: The IUCN Red List of Threatened Species. Version 2014.3. <>. Downloaded on 27 March 2015.
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