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Anaxyrus houstonensis

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA AMPHIBIA ANURA BUFONIDAE

Scientific Name: Anaxyrus houstonensis
Species Authority: (Sanders, 1953)
Common Name(s):
English Houston Toad
Synonym(s):
Bufo houstonensis Sanders, 1953

Assessment Information [top]

Red List Category & Criteria: Endangered C2a(ii) ver 3.1
Year Published: 2004
Date Assessed: 2004-04-30
Assessor(s): Geoffrey Hammerson, Donald Shepard
Reviewer(s): Global Amphibian Assessment Coordinating Team (Simon Stuart, Janice Chanson, Neil Cox and Bruce Young)
Justification:
Listed as Endangered because its population size is estimated to number fewer than 2,500 mature individuals, with more than 95% of the individuals in a single sub-population, and it is experiencing a continuing decline.
History:
1996 Endangered
1994 Endangered (Groombridge 1994)
1990 Endangered (IUCN 1990)
1988 Endangered (IUCN Conservation Monitoring Centre 1988)
1986 Endangered (IUCN Conservation Monitoring Centre 1986)

Geographic Range [top]

Range Description: Historically, this species ranged across the central coastal region of Texas. Houston toads disappeared from the Houston area (Harris, Fort Bend and Liberty counties) during the 1960s following an extended drought and the rapid urban expansion of the city of Houston. Although this species has been found in nine additional counties (Austin, Bastrop, Burleson, Colorado, Lavaca, Lee, Leon, Milam, Robertson) as recently as the 1990s, several of these populations have not been seen since they were first discovered. Of the few remaining populations, the largest is in Bastrop County.
Countries:
Native:
United States
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: At least 2000 adults occur in Bastrop County; unknown numbers probably persist in seven other counties (http://www.tpwd.state.tx.us/nature/endang/htoad.htm; Seal 1994). Recent trend analyses suggest that Houston toads are declining in Bastrop State Park, which lies near the centre of its critical habitat in Bastrop County.
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: Houston toads are restricted to areas with sandy, friable soil such as loblolly pine forest, mixed deciduous forest, post oak savannah, and coastal prairie. Breeding may occur from late January to late June, but usually earlier than May, in rain pools, flooded fields, roadside ditches, and natural or man-made ponds. Optimal habitats are non-flowing, fishless pools that persist for at least 60 days (long enough for larvae to metamorphose). Houston toads are nocturnal, spending daylight hours in burrows, buried in sand, or under leaf-litter, pine duff, or surface objects.
Systems: Terrestrial

Threats [top]

Major Threat(s): Habitat conversion poses the most serious threat to the Houston toad. Several populations were eliminated with the expansion of Houston, and the largest remaining population in Bastrop County is also under intense and immediate threat from urbanization and recreational over-development. Many Houston toads are killed each year by automobiles. Roadway mortality will increase as human populations continue to increase within the species’ habitat and as the habitat continues to be dissected by more roads. Road construction further isolates populations and disrupts or prevents the movement of individual toads between populations. This movement of toads is necessary to maintain gene flow, and thus genetic diversity, and to supplement small or declining local populations. It is possible to build roads with underpasses or other structures that allow toads and other wildlife to pass safely beneath the roads. While converting woodlands to pastures or ploughed fields destroys Houston toad habitat and favours the proliferation of other toad species, certain agricultural practices can be beneficial to Houston toads. These include maintaining low to moderate numbers of livestock to avoid overgrazing, protecting pond habitat from livestock and predatory fish, planting native bunchgrasses instead of sod-forming grasses such as Bermuda grass (which are difficult for the toads to move through), and conserving large blocks of woodlands. Certain forestry practices may benefit the Houston toad, while others, such as clear cutting, are harmful. Thinning and burning have been shown to benefit some species of amphibians and reptiles by opening up the forest canopy and allowing more sunlight to reach the forest floor. This practice encourages the growth of vegetation and, in turn, increases insect numbers. This may be beneficial to the Houston toad. Other threats that often appear in conjunction with the factors outlined above include prolonged drought and the presence of fire ants, an unwelcome species from Brazil. Fire ants have been observed preying on toadlets as they leave their breeding pond. Fire ants thrive in open, sunny areas where the soil has been disturbed and woody vegetation uprooted, as in agricultural fields and urban areas. Protecting large forested areas is one of the most effective deterrents to fire ants. Where fire ant control with pesticides is necessary, mounds should be treated individually, rather than broadcasting the chemicals, to avoid impacting other invertebrates that the Houston toad eats (see http://ifw2es.fws.gov/HoustonToad).

Conservation Actions [top]

Conservation Actions: The Houston toad was the first amphibian granted protection under the U.S. Endangered Species Act. A critical habitat was designated in 1978 in Bastrop and Burleson counties, in areas supporting the largest populations known at that time. However, the population within critical habitat in Burleson County has not been seen since 1983. In the 1970s, the state of Texas acquired land within designated critical habitat in Bastrop County adjacent to Buescher and Bastrop state parks to aid in conservation. Additionally, an effort was started in 1978 by the Houston Zoo to identify remaining Houston toad populations and supplement them or establish new populations in protected areas using wild-caught adults, naturally deposited eggs, or captive-reared juveniles and adults. However, new populations were not established in spite of introducing over 500,000 individuals (adults, juveniles, larvae) into sites at the Attwater Prairie Chicken National Wildlife Refuge. Research is urgently needed to determine the status of Houston toad populations outside Bastrop County and promote conservation efforts in these areas. Research is also critical to determine which management practices are most conducive to the Houston toad and the ecosystem on which it depends. The Houston Toad Recovery Plan was published by the U.S. Fish and Wildlife Service (USFWS) in 1984. The Texas Parks and Wildlife Department and the USFWS have jointly prepared a brochure for private landowners who wish to implement their agricultural practices in ways that are compatible with the needs of the Houston toad and the Texas Forest Service has formed a committee to develop management practices that protect the Houston toad and its habitat. Additionally, the USFWS is working with community leaders, private landowners, and conservation organizations to develop and implement a regional Habitat Conservation Plan for Bastrop County, which would provide for the issuance of endangered species permits that allow development to proceed while ensuring permanent habitat protection. The USFWS also has established a fund with the National Fish and Wildlife Foundation to assist in local habitat protection efforts for the Houston toad.

Bibliography [top]

Bartlett, R.D. and Bartlett, P.P. 1999. A Field Guide to Florida Reptiles and Amphibians. Gulf Publishing Company, Houston, TX, USA.

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

Brown, L.E. 1971. Natural hybridization and trend toward extinction in some relict Texas toad populations. Southwestern Naturalist: 185-199.

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

Brown, L.E., McClure, W.L., Potter, Jr, F.E., Scott, Jr, N.J. and Thomas, R.A. 1984. Recovery plan for the Houston toad (Bufo houstonensis). U.S. Fish and Wildlife Service, Albuquerque, New Mexico.

Bury, R.B., Dodd, Jr., C.K. and Fellers, G.M. 1980. Conservation of the Amphibia of the United States: a review. Resource Publication: 1-34.

Campbell, L. 1995. Endangered and Threatened Animals of Texas: Their Life History and Management. Texas Parks and Wildlife Department, Endangered Resources Branch, Austin, Texas.

Conant, R. and Collins, J.T. 1991. A Field Guide to Reptiles and Amphibians: Eastern and Central North America. Third Edition. Houghton Mifflin Company, Boston, Massachusetts.

Dixon, J.R. 2000. Amphibians and Reptiles of Texas. Second edition. Texas A & M University Press, College Station, College Station, Texas.

Dodd, Jr, C.K. and Seigel, R.A. 1991. Relocation, repatriation, and translocation of amphibians and reptiles: are they conservation strategies that work? Herpetologica: 336–350.

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

Gaston, M.A., Forstner, M.R.J. and Dixon, J.R. 2001. Geographic distribution: Bufo houstonensis. Herpetological Review: 269.

Hillis, D.M., Hillis, A.M. and Martin, R.F. 1984. Reproductive ecology and hybridization of the endangered Houston toad (Bufo houstonensis). Journal of Herpetology: 56-72.

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

Jacobson, N.L. 1989. Breeding dynamics of the Houston toad. Southwestern Naturalist: 374-380.

Kennedy, J.P. 1961. Spawning season and experimental hybridization of the Houston toad, Bufo houstonensis. Herpetologica: 239-245.

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.

Quinn, H.R. and Mengden, G. 1984. Reproduction and growth of Bufo houstonensis (Bufonidae). Southwestern Naturalist: 189-195.

Seal, U.S. 1994. Houston toad (Bufo houstonensis) population and habitat viability assessment. IUCN/SSC Conservation Breeding Specialist Group, Apple Valley, Minnesota.

U.S. Fish and Wildlife Service. 1980. Selected vertebrate endangered species of the seacoast of the United States - the Houston toad. FWS/OBS-80/01.38.

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

U.S. Fish and Wildlife Service. In jeopardy-- America's endangered species. Houston toad. (no date).


Citation: Geoffrey Hammerson, Donald Shepard 2004. Anaxyrus houstonensis. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 16 September 2014.
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