Anaxyrus baxteri - (Porter, 1968)
Wyoming Toad
Synonym(s): Bufo baxteri Porter, 1964 ;Bufo hemiophrys baxteri
Taxonomic Status: Accepted
Related ITIS Name(s): Anaxyrus baxteri (Porter, 1968) (TSN 773512)
Unique Identifier: ELEMENT_GLOBAL.2.101600
Element Code: AAABB01220
Informal Taxonomy: Animals, Vertebrates - Amphibians - Frogs and Toads
Kingdom Phylum Class Order Family Genus
Animalia Craniata Amphibia Anura Bufonidae Anaxyrus
Genus Size: D - Medium to large genus (21+ species)
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Concept Reference
Concept Reference: Smith, H. M., D. Chiszar, J. T. Collins, and F. van Breukelen. 1998. The taxonomic status of the Wyoming toad, Bufo baxteri Porter. Contemporary Herpetology 1998(1):http//
Concept Reference Code: A98SMI01NAUS
Name Used in Concept Reference: Bufo baxteri
Taxonomic Comments: Smith et al. (1998) examined morphological variation in Bufo hemiophrys and concluded that the population in Wyoming (Bufo hemiophrys baxteri) warrants recognition as a distinct species (Bufo baxteri).
Conservation Status

NatureServe Status

Global Status: G1
Global Status Last Reviewed: 30Jun2004
Global Status Last Changed: 11Oct2001
Rounded Global Status: G1 - Critically Imperiled
Reasons: Very small range and declining population in a portion of the Laramie Basin, Wyoming; threats include chytrid fungal infection and prolonged drought; population has been maintained by releases of captive-reared toadlets.
Nation: United States
National Status: N1 (05Nov1996)

U.S. & Canada State/Province Status
United States Wyoming (S1)

Other Statuses

U.S. Endangered Species Act (USESA): LE: Listed endangered (04May1973)
U.S. Fish & Wildlife Service Lead Region: R6 - Rocky Mountain
IUCN Red List Category: EW - Extinct in the wild

NatureServe Global Conservation Status Factors

Range Extent: <100 square km (less than about 40 square miles)
Range Extent Comments: Laramie Basin, Wyoming. Historically known from areas within about 50 km of Laramie. Extant only at Mortenson Lake National Wildlife Refuge (USFWS 2002). A population at a former reintroduction site (Lake George on the Hutton Lake National Wildlife Refuge) has been lost due to drought (USFWS 2002).

Historical range extent was approximately 2,330 sq km (USFWS data).

Number of Occurrences: 1 - 5
Number of Occurrences Comments: As of 2002, there was one known extant occurrence (USFWS 2002).

Population Size: 1 - 50 individuals
Population Size Comments: In June 2002, a survey at Mortenson Lake NWR yielded 124 yearlings and 4 adults (USFWS 2002). Limited natural reproduction and recruitment of a few metamorphosed juveniles ocurred in 2002 (USFWS 2002). Rush Lake and Lake George were too dry for productive survey work in 2002.

Number of Occurrences with Good Viability/Integrity: None (zero)
Viability/Integrity Comments: The extant occurrence likely would be extirpated without recent annual releases of captive-reared toadlets.

Overall Threat Impact: Very high - high
Overall Threat Impact Comments: Mortenson Lake, site of the only known extant population, is infected with the amphibian chytrid fungus (Batrachochytrium dendrobatidis) (USFWS 2002). 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 may also limit the abundance of Wyoming toads in the Laramie Basin. The cause of the original decline remains unknown but may be associated with the invasion of B. dendrobatidis into the area (USFWS 2002). Mortenson Lake recently has become more saline (and less suitable for toads) as a result of drought-related increases in evaporation (USFWS 2002). Salt-cedar was found (and removed) at Hutton Lake NWR in 2002. This plant has the potential to reduce habitat suitability (USFWS 2002).

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, likely mustelids, killed several radio-tagged individuals in 1998 (Parker et al. 2000).

Short-term Trend: Decline of 10-30%
Short-term Trend Comments: At Mortenson Lake, there has been no natural reproduction by wild toads since 1991; population is maintained through release of captive-reared young (Parker et al. 2000). Limited reproduction occurred in the field in 2002 (USFWS 2002). Despite releases of captive-reared individuals, the population at Mortenson Lake NWR appears to be declining (USFWS 2002).

Long-term Trend: Decline of >90%
Long-term Trend Comments: Large decline. Common in the 1950s; large decline in the 1960s and 1970s; thought to be extinct in the wild in the mid-1980s; found at Mortenson Lake in 1987; captive propagation began in the mid-1990s using toads from Mortenson Lake (USFWS 2002).

Intrinsic Vulnerability: Moderately vulnerable

Environmental Specificity: Moderate. Generalist or community with some key requirements scarce.

Other NatureServe Conservation Status Information

Protection Needs: Encourage pesticide spraying that it is compatible with toad recovery.

Global Range: (<100 square km (less than about 40 square miles)) Laramie Basin, Wyoming. Historically known from areas within about 50 km of Laramie. Extant only at Mortenson Lake National Wildlife Refuge (USFWS 2002). A population at a former reintroduction site (Lake George on the Hutton Lake National Wildlife Refuge) has been lost due to drought (USFWS 2002).

Historical range extent was approximately 2,330 sq km (USFWS data).

U.S. States and Canadian Provinces
Color legend for Distribution Map
Endemism: endemic to a single state or province

U.S. & Canada State/Province Distribution
United States WY

Range Map
Note: Range depicted for New World only. The scale of the maps may cause narrow coastal ranges or ranges on small islands not to appear. Not all vagrant or small disjunct occurrences are depicted. For migratory birds, some individuals occur outside of the passage migrant range depicted. For information on how to obtain shapefiles of species ranges see our Species Mapping pages at

Range Map Compilers: IUCN, Conservation International, NatureServe, and collaborators, 2004

U.S. Distribution by County Help
State County Name (FIPS Code)
WY Albany (56001)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
10 Upper Laramie (10180010)+
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
Basic Description: A two-inch toad.
Reproduction Comments: Lays eggs generally from mid-May to mid-June. Larvae metamorphose by early August. Females in the wild likely first breed when 2-3 years old. Breeding aggregations generally are small.
Non-Migrant: N
Locally Migrant: N
Long Distance Migrant: N
Mobility and Migration Comments: Movements appear to be limited but have not been well studied.
Lacustrine Habitat(s): Shallow water
Palustrine Habitat(s): HERBACEOUS WETLAND, Riparian, TEMPORARY POOL
Terrestrial Habitat(s): Grassland/herbaceous
Special Habitat Factors: Benthic, Burrowing in or using soil
Habitat Comments: Historically associated with floodplain ponds along the Big and Little Laramie Rivers; use of lakes may have been limited due to saline conditions; irrigation may have flushed out the lakes and made them more suitable for toads (George Baxter). Currently occurs in the vicinity of lakes and adjacent meadows. Uses rodent burrows for shelter. Eggs and larvae develop in shallow water.
Adult Food Habits: Invertivore
Immature Food Habits: Herbivore
Food Comments: Metamorphosed toads eat a various small terrestrial arthropods. Larvae eat organic debris, algae, and plant tissue.
Phenology Comments: Inactive during cold season.
Colonial Breeder: Y
Economic Attributes Not yet assessed
Management Summary
Management Requirements: Current management focuses on captive breeding and release of larvae and toadlets at Mortenson Lake National Wildlife Refuge (USFWS 2002). Several thousand toadlets were released at Mortenson Lake each year in the early 2000s (USFWS 2002). Efforts are being made to establish additional suitable release sites (USFWS 2002).

A fall grazing regime is utilized to thin dense vegetation around the shoreline of Mortenson Lake to create open areas for the toad. Grazing on Hutton Lake NWR was halted in 2002 due to the more severe drought conditions experienced at that refuge.

Biological Research Needs: Develop captive/wild infectious disease management protocols; gather disease information and begin research to reduce the rate of mortality in the captive population; increase the long-term survival rate of captive yearlings from 50% to 80%; improve captive larval rearing success from 25% to 95%; assemble existing and collect new, accurate demographic and ecological data from the Wyoming toad in the wild; increase the number of viable (captive) eggs by increasing the egg hatch rate from 27% to 95%; develop the funding sources necessary to hire a full-time, permanent Recovery Coordinator; using existing data, determine the appropriate ecological criteria for identifying new releasesites for the establishment of wild populations, and develop a detailed process for choosing new sites; determine mortality-causing disease factors at proposed release sites; conduct molecular genetic analyses (DNA fingerprinting and mtDNA) to determine the overall degree of relatedness among those individuals thought to constitute the captive population's founder base, to assess the potential for the identification of new genes within the "B Line" of captive Wyoming toads; establish the taxonomic relationship between Bufo baxteri and B. hemiophrys (this is from the Wyoming Toad (Bufo baxteri) Population and Habitat Viability Assessment (PHVA), which summarizes the results of a workshop held in Laramie, Wyoming, in February 2001).
Population/Occurrence Delineation
Group Name: Bufonid Toads

Use Class: Not applicable
Subtype(s): Breeding Site
Minimum Criteria for an Occurrence: Occurrences are based on evidence of historical presence, or current and likely recurring presence, at a given location. Such evidence minimally includes collection or reliable observation and documentation of one or more individuals (including larvae or eggs) in or near appropriate habitat where the species is presumed to be established and breeding.
Separation Barriers: Busy major highway such that toads rarely if ever cross successfully; roads with nonpermeable barriers to toad movement; urbanized areas dominated by buildings and pavement.
Separation Distance for Unsuitable Habitat: 1 km
Separation Distance for Suitable Habitat: 5 km
Separation Justification: Opportunistic observations of various toad species in lowland habitats indicate regular movements of up to at least several hundred meters from the closest known breeding site (G. Hammerson, pers. obs.). Sweet (1993) recorded movements of up to 1 km in Bufo californicus. In defining critical habitat for B. californicus, USFWS (2000) included breeding streams and upland areas within a 25-m elevational range of each essential stream reach and no more than 1.5 km away from the stream. In northwestern Utah, Thompson (2004) recorded movements of Bufo boreas of up to 5 km across upland habitat between two springs during the summer-fall season. Another toad moved 1.3 km between May of one year and May of the next year; the following June it was back at the original breeding location (Thompson 2004). Most studies of toad movements have not employed radiotelemetry and were not designed to detect long-range movements or dispersal.

The separation distance for unsuitable habitat reflects the nominal minimum value of 1 km. The separation distance for suitable habitat reflects the good vagility of toads, their ability to utilize ephemeral or newly created breeding sites, and the consequent likely low probability that two occupied locations separated by less than several kilometers of suitable habitat would represent truly independent populations over the long term.

Inferred Minimum Extent of Habitat Use (when actual extent is unknown): .5 km
Date: 27Apr2005
Author: Hammerson, G.
Population/Occurrence Viability
U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
NatureServe Conservation Status Factors Edition Date: 04Apr2011
NatureServe Conservation Status Factors Author: Hammerson, G.
Element Ecology & Life History Edition Date: 02Apr2003
Element Ecology & Life History Author(s): Hammerson, G.

Zoological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

  • Andersen, M.D. 2011. Maxent-based species distribution models. Prepared by Wyoming Natural Diversity Database for use in the pilot WISDOM application operational from inception to yet-to-be-determined date of update of tool.

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  • Anonymous. 2005. Statewide programmatic biological assessment for the Wyoming toad (Bufo baxteri). Final report submitted to BLM Wyoming State Office, 5353 Yellowstone Road, Cheyenne, Wyoming 82003-1828.


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  • Garber, C.S. and P.A. White. 1991. A report on the locations of formerly occupied sites of the federally Endangered Wyoming toad (BUFO HEMIOPHRYS BAXTERI) and a summary of areas searched in historical habitat. Unpublished report prepared by the Wyoming Natural Diversity Database for the U.S. Fish and Wildlife Service, Region 6, Wyoming State Office, 2617 Lincoln Way, Cheyenne, WY.

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