Globally Threatened Amphibian Species Part 1

Globally Threatened Amphibian Species 185
CR Bufo holdridgei Taylor, 1952
Critically Endangered A2ace; B1ab(v)
Order, Family: Anura, Bufonidae
Country Distribution: Costa Rica
Current Population Trend: Decreasing
© Wayne Van Devender
Geographic Range This species occurs on the Volcán Barva, Cordillera Central, Costa Rica, at 200-2,200m asl
(Savage 2002).
Population It was formerly common in appropriate habitat and during the breeding season at the onset of the rainy
season (2,765 males were seen visiting two pools in an eight-day period; Nowak and Robinson 1975). It has not been
seen since 1986 despite repeated searching throughout its range, and it is possible that it is now extinct.
Habitat and Ecology It lives in lower montane rainforest. It is a fossorial species, and may be found under surface
debris within the forest during periods of heavy rain, but otherwise concentrates on mossy stream banks during dry
periods. It is an explosive breeder that lays its eggs in forest floor pools, as well as in man-made drainage ditches
(Savage 2002).
Major Threats Although not proven, the main cause of the population decline is likely to be chytridiomycosis perhaps
in synergy with the effects of climate change.
Conservation Measures The entire known range of this species is protected in Parque Nacional Braulio Carrillo,
20km north-east of the capital of San José. Surveys are urgently required to determine whether or not the species
survives and, in view of the threat of chytridiomycosis, surviving individuals might need to form the basis for the
establishment of an ex-situ population.
Bibliography: Novak, R.M. and Robinson, D.C. (1975), Savage, J.M. (2002)
Data Providers: Federico Bolaños, Gerardo Chaves
EN Bufo houstonensis Sanders, 1953
Endangered C2a(ii)
Order, Family: Anura, Bufonidae
Country Distribution: United States of America
Current Population Trend: Decreasing
© Danté Fenolio/www.anotheca.com
Geographic Range 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.
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.
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.
Major Threats 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
HOUSTON TOAD
habitat and favours the proliferation of other toad species, certain agricultural practices can be benefi cial 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 benefi cial to the Houston toad. Other threats that often appear in conjunction with the factors
outlined above include prolonged drought and the presence of fi re 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 Measures The Houston toad was the fi rst 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: Bartlett, R.D. and Bartlett, P.P. (1999), Blackburn, L., Nanjappa, P. and Lannoo, M.J. (2001), Brown, L.E. (1971), Brown,
L.E. (1973), Brown, L.E. et al. (1984), Bury, R.B., Dodd, Jr., C.K. and Fellers, G.M. (1980), Campbell, L. (1995), Conant, R. and Collins, J.T.
(1991), Dixon, J.R. (2000), Dodd, Jr, C.K. and Seigel, R.A. (1991), Frost, D.R. (1985), Gaston, M.A., Forstner, M.R.J. and Dixon, J.R. (2001),
Hillis, D.M., Hillis, A.M. and Martin, R.F. (1984), Jacobson, N.L. (1989), Kennedy, J.P. (1961), Matthews, J.R. and Moseley, C.J. (eds)
(1990), Quinn, H.R. and Mengden, G. (1984), Seal, U.S. (1994), U.S. Fish and Wildlife Service, U.S. Fish and Wildlife Service (1980b),
U.S. Fish and Wildlife Service (1990a)
Data Providers: Geoffrey Hammerson, Donald Shepard
EN Bufo ibarrai Stuart, 1954
Endangered B1ab(iii)
Order, Family: Anura, Bufonidae
Country Distribution: Guatemala, Honduras
Current Population Trend: Decreasing
© Twan Leenders
Geographic Range This species occurs at moderate and intermediate elevations of central and southern Guatemala
and the Sierra de las Minas, eastern Guatemala, from 1,360-1,980m asl. Its range has also recently been extended
into contiguous regions of Honduras in the western ranges of the Southern Cordillera Region in the departments of
Intibuca, Lemipira and Ocotepeque, up to 2,020m asl (Mendelson et al. 2005). However, McCranie and Wilson (2002)
refer all Honduran material to Bufo coccifer.
Population This species persists in small numbers in appropriate habitat. Nearly continuous field work throughout
the range of this species in Guatemala between 1989 and 1998 produced less than 10 observations.
Habitat and Ecology It occurs in pine-oak or premontane or lower montane moist forest, and breeds in ponds,
marshes and wet meadows. Males have been observed calling from the banks of ponds.
Major Threats Its range is severely fragmented due to habitat loss, primarily due to agricultural activities. Formerly
robust populations in Guatemala are now extirpated following severe alteration of montane wetlands and cloud
forests, and may well have succumbed to the effects of chytrid, which has been documented in other anuran species
in the same area (Mendelson et al. 2004).
Conservation Measures A portion of the range previously occurred in the Reserva de la Biósfera Sierra de las Minas
in Guatemala, but it has now been extirpated from this region. Protection of the remaining habitat of this species is
urgently required. Given the threat of chytrid, this species requires close population monitoring.
Bibliography: Campbell, J.A. (2001), McCranie, J.R. and Wilson, L.D. (2002b), Mendelson III, J.R. (2001), Mendelson III, J.R. et al.
(2004), Mendelson III, J.R. et al. (2005)
Data Providers: Manuel Acevedo, Bruce Young