Anaxyrus nelsoni - (Stejneger, 1893)
Amargosa Toad
Synonym(s): Bufo nelsoni Stejneger, 1893
Taxonomic Status: Accepted
Related ITIS Name(s): Anaxyrus nelsoni (Stejneger, 1893) (TSN 773526)
Unique Identifier: ELEMENT_GLOBAL.2.103677
Element Code: AAABB01190
Informal Taxonomy: Animals, Vertebrates - Amphibians - Frogs and Toads
Image 12107

© Glenn H. Clemmer

 
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
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Concept Reference: Frost, D. R. 2002. Amphibian Species of the World: an online reference. V2.21 (15 July 2002). Electronic database available at http://research.amnh.org/herpetology/amphibia/index.html.
Concept Reference Code: N02FRO01NAUS
Name Used in Concept Reference: Bufo nelsoni
Taxonomic Comments: Bufo nelsoni formerly was included in B. boreas. Biochemical data support full species status (Feder 1977).

Phylogenetic analyses of mtDNA data from throughout the range of the Bufo (Anaxyrus) boreas species group (including boreas, canorus, exsul, and nelsoni) by Goebel et al. (2009) identified three major haplotype clades. The Northwest clade (NW) includes both subspecies of boreas (boreas and halophilus) and divergent minor clades in the middle Rocky Mountains, coastal, and central regions of the west and Pacific Northwest. The Southwest (SW) clade includes exsul, nelsoni, and minor clades in southern California. Bufo (Anaxyrus) canorus, previously identified as paraphyletic, has populations in both the NW and SW major clades. The Eastern major clade (E) includes three divergent lineages from southern Utah, the southern Rocky Mountains, and north of the Great Basin at the border of Utah and Nevada. Goebel et al. (2009) tentatively suggested that some or many of the clades might warrant recognition as distinct species. However, the authors refrained from delineating new species circumscriptions, noting that additional research might suggest different taxonomic outcomes (e.g., recognizing the traditionally defined Bufo canorus as two distinct species or, conversely, combining it with other minor groups and thus broadening its scope).
Conservation Status
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NatureServe Status

Global Status: G2
Global Status Last Reviewed: 12Nov2003
Global Status Last Changed: 12Jan1999
Rounded Global Status: G2 - Imperiled
Reasons: Range is very small (about 20 sites in one county in Nevada); more common than previously known; conservation actions have been initiated to improve degraded habitat.
Nation: United States
National Status: N2 (12Jan1999)

U.S. & Canada State/Province Status
United States Nevada (S2)

Other Statuses

IUCN Red List Category: EN - Endangered

NatureServe Global Conservation Status Factors

Range Extent: <100 square km (less than about 40 square miles)
Range Extent Comments: Riparian habitats associated with the Amargosa River, tributary springs of the Amargosa River in Oasis Valley, and isolated spring systems near Beatty, Nye County, Nevada (USFWS, Federal Register, 1 March 1996), at an elevation of approximately 3,300-3,500 feet (1,000-1,070 m).

Area of Occupancy: 1-25 4-km2 grid cells
Area of Occupancy Comments: Occurs along a 16-km stretch of the Amargosa River and interconnected spring systems (Burroughs 1999).

Number of Occurrences: Unknown
Number of Occurrences Comments: Occurred in about 20 or more sites as of the mid-1990s.

Population Size: 250 - 2500 individuals
Population Size Comments: Total adult population size is uncertain but likely is at least several hundred. Thousands were reported in 1958; estimates of the size of the metamorphosed population at 10 sites in 1993 and 1994 ranged from 30 to 130, but some probably occupied sites have not been surveyed in recent years (USFWS, Federal Register, 1 March 1996).

Overall Threat Impact: Medium
Overall Threat Impact Comments: Factors that may be adversely affecting the toad and its habitat include effects of variable rainfall on small populations, livestock and feral burro grazing and trampling, off-road vehicle use, grading for flood control, activities related to commercial development, non-native predators (catfish, crayfish, bullfrog [Jones et al. 2003]), water pollution, and water diversion (Froglog, December 1994). Trampling of tadpoles by cattle may be negatively affecting the LaFleur population, which also may be threatened by road widening (Route 95). Expansion of non-native saltcedar may degrade habitat (Burroughs 1999).

Short-term Trend: Decline of 10-30%
Short-term Trend Comments: Over the past few decades, reportedly has declined greatly from former range and abundance (Altig and Dodd 1987), but recent surveys found that distribution and abundance were greater than previously known. Surveys at 20 sites since 1990 yielded the following results: apparently extirpated from one spring, decreased abundance at four springs, fluctuating but relatively constant populations at 15 sites (USFWS, Federal Register, 1 March 1996; see also unpublished 1993 and 1994 reports by Hoff, prepared for the USFWS, Reno, Nevada).

Long-term Trend: Decline of 30-50%

Intrinsic Vulnerability: Moderately vulnerable

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

Other NatureServe Conservation Status Information

Inventory Needs: Ongoing population monitoring is needed.

Protection Needs: Exclude off-road vehicles; protect riparian zones from excessive grazing; restore habitat; prohibit excessive collecting of specimens. See USFWS (Federal Register, 1 March 1996) and Burroughs (1999) for brief descriptions of recent conservation activities (habitat protection/restoration).

Distribution
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Global Range: (<100 square km (less than about 40 square miles)) Riparian habitats associated with the Amargosa River, tributary springs of the Amargosa River in Oasis Valley, and isolated spring systems near Beatty, Nye County, Nevada (USFWS, Federal Register, 1 March 1996), at an elevation of approximately 3,300-3,500 feet (1,000-1,070 m).

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 NV

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 www.natureserve.org/conservation-tools/data-maps-tools.

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


U.S. Distribution by County Help
State County Name (FIPS Code)
NV Nye (32023)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
18 Upper Amargosa (18090202)+
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Basic Description: A 2-3-inch toad with a narrow head and short limbs.
Reproduction Comments: Breeds mid-March to early April (Stebbins 1985). Metamorphosing individuals observed in late April (Altig and Dodd 1987).
Non-Migrant: Y
Locally Migrant: N
Long Distance Migrant: N
Riverine Habitat(s): Pool, SPRING/SPRING BROOK
Palustrine Habitat(s): HERBACEOUS WETLAND, Riparian
Special Habitat Factors: Benthic, Burrowing in or using soil, Fallen log/debris
Habitat Comments: Usually found near water at desert springs and outflow. Vegetation bordering water consists of cottonwood trees, cattails, and sedges. May congregate at street lights to feed on attracted insects (Burroughs 1999). Eggs and larvae develop in spring waters (open areas with little vegetation at LaFleur).
Adult Food Habits: Invertivore
Adult Phenology: Crepuscular, Diurnal, Hibernates/aestivates, Nocturnal
Immature Phenology: Crepuscular, Diurnal, Hibernates/aestivates, Nocturnal
Phenology Comments: Diurnal in spring, becoming nocturnal in summer (Stebbins 1985).
Colonial Breeder: Y
Length: 8 centimeters
Economic Attributes Not yet assessed
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Management Summary
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Management Requirements: Breeding areas could be protected from cattle trampling by erecting a fence (LaFleur site, Altig and Dodd 1987). Pesticide use should be restricted in breeding areas. Pumping of ground water and channelization should be restricted (Bury et al. 1980).
Population/Occurrence Delineation
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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
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Edition Date: 12Nov2003
NatureServe Conservation Status Factors Author: Hammerson, G.
Element Ecology & Life History Edition Date: 28Mar1995
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).

References
Help
  • Altig, R., and C. K. Dodd, Jr. 1987. The status of the Amargosa toad (BUFO NELSONI) in the Amargosa River drainage of Nevada. Southwestern Naturalist. 32:276-278.

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

  • Burroughs, M. 1999. Making room for the Amargosa toad. Endangered Species Bulletin 24:10-11.

  • Bury, R. B., C. K. Dodd, Jr., and G. M. Fellers. 1980. Conservation of the Amphibia of the United States: a review. U.S. Fish and Wildlife Service, Washington, D.C., Resource Publication 134. 34 pp.

  • Feder, J. H. 1977. Genetic variation and biochemical systematics in western Bufo. Unpub. M.A. thesis, Univ. California, Berkeley.

  • Feder, J.H. 1977. Genetic variation and biochemical systematics in western Bufo. Unpub. M.A. thesis, Univ. California, Berkeley.

  • Frost, D. R. 2002. Amphibian Species of the World: an online reference. V2.21 (15 July 2002). Electronic database available at http://research.amnh.org/herpetology/amphibia/index.html.

  • Frost, D. R. 2010. Amphibian Species of the World: an Online Reference. Version 5.4 (8 April 2010). Electronic Database accessible at http://research.amnh.org/herpetology/amphibia/index.php. American Museum of Natural History, New York, USA.

  • Goebel, A. M., T. A. Ranker, P. S. Corn, and R. G. Olmstead. 2009. Mitochondrial DNA evolution in the Anaxyrus boreas species group. Molecular Phylogenetics and Evolution 50:209-225.

  • Jones, D., E. T. Simandle, C. R. Tracy, and B. Hobbs. 2003. Bufo nelsoni (Amargosa toad). Predation. Herpetological Review 34:229.

  • NatureServe. Central Databases. Arlington, Virginia. U.S.A. Online. Available: http://www.natureserve.org/explorer/

  • Stebbins, R. C. 1951. Amphibians of western North America. University of California Press, Berkeley. 539 pp.

  • Stebbins, R. C. 1985a. A field guide to western reptiles and amphibians. Second edition. Houghton Mifflin Company, Boston, Massachusetts. xiv + 336 pp.

  • Stebbins, R. C. 2003. A field guide to western reptiles and amphibians. Third edition. Houghton Mifflin Company, Boston.

  • U.S. Fish and Wildlife Service (USFWS). 1989. Endangered and threatened wildlife and plants: animal notice of review. Federal Register 54:554-579.

  • U.S. Fish and Wildlife Service (USFWS). 1989a. Endangered and threatened wildlife and plants; animal notice of review. Federal Register, Department of the Interior 54(4): 554-579.

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