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Anaxyrus houstonensisHouston Toad

By Nathan Fostey

Geographic Range

The Houston toad is limited to an extremely small range in southeastern Texas. Since its discovery in 1953 it has never been found north of Burleson County, south of Fort Bend County, east of Liberty County, or west of Bastrop County.

Habitat

Tadpoles are found in non-flowing pools that last for at least 60 days. Adults are restricted to sandy soils and prefer wooded areas interspersed with open grass. They are also found in coastal prairies. Within these habitats they are never far from water, and during the breeding season are located almost exclusively near ponds and rain pools.

Physical Description

The upper part of Houston toads is usually light brown in color, though it may sometimes be reddish. It possesses a variable number of dark brown or black spots. The underbelly is cream colored and usually very mottled. There is always at least one brown spot on the pectoral region. Females are 52-80 mm long (snout to vent). Males are smaller, being 45-70 mm long. Tadpoles are 13.7-22 mm long. Tadpole bodies and the upper 75% of their tails are heavily pigmented.

Development

Reproduction

Breeding occurs between the end of January and the end of June, but peaks in late February. Early breeding often begins when the prior 24-hour period's temperature has not fallen below 14 degrees C. Mating occurs at night near shallow pools of water or ponds. Males begin their mating calls twenty minutes before sunset while still in their burrows. After ten minutes they begin moving toward a breeding pond, arriving between sunset and midnight. Once there, they seek elevated places from which to call. This call consists of a long high pitched trill. The first females begin arriving several hours after sunset. Once a female has selected a mate, the male remains clasped to the female for at least six hours. Between 500 and 6000 eggs are laid and fertilized in the water during the early morning hours. Afterwards males issue a release call consisting of a short barely audible release vibration, and an even shorter release chirp. Eggs hatch in seven days and metamorphosis begins in 60-65 days. Males reach sexual maturity in 1 year, and females at 1-2 years. Males typically breed for 2 seasons; females, for at least as long.

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)

Behavior

Houston toads are primarily diurnal throughout most of the year. During the breeding season they are active during most hours of the day and night, with activity concentrated in the evening. During days before breeding nights the toads take solitary shelter in small mammal burrows. These burrows may be 1-40 m from a water source. Tadpoles are nocturnal, spending the day at the bottom of their pool or pond. At night they feed at the surface. The chief predators of adults are hogback snakes, herons, egrets, raccoons, skunks, and coyotes. Fire ants have been known to attack and consume young terrestrial toads. Mating calls occur when air temperature is 4.5 to 24.0 degrees C, and water temperature is 14.5 to 23.0 degrees C.

Food Habits

Tadpoles feed primarily on pollen (usually from nearby pines), the jelly envelopes of other recently hatched Houston toads, and algae on floating leaves. Adults feed primarily on ground beetles, although they have been known to eat smaller toads and ants. They utilize two methods to capture prey: sit-and-wait and active search. For the sit-and-wait method, A. houstonensis first digs a small depression in the soil with its powerful hind legs. The toad then rests in the depression and scans the surrounding area for movement. When prey is detected B. Houstonensis leaps forwards and takes the prey into its mouth. Depressions are abandoned many times per day and new ones dug nearby.

Economic Importance for Humans: Positive

Besides the aesthetics of the Houston toad's bell-like calls (perhaps appreciated only by enthusiasts), it has little economic value to humans. Although Houston toads do limit insect populations, other more abundant sympatric toad species also fulfill this role.

Conservation Status

Throughout the 1950s the Houston toad's populations declined sharply. Regional drought was the largest contributor to this, followed by loss of suitable habitat due to land development. Soil erosion, cattle grazing, and pesticide run-off have all limited the number of suitable breeding ponds. Conservation efforts have attempted to counter habitat loss. Most notably have been two land purchases in the 1970s. In 1971 the University of Texas Environmental Science Department purchased 1400 acres of forested land adjacent to Bastrop State Park to use as a study area. In 1979 the Texas Parks and Wildlife Department purchased another 717 acres. In 1974 the Houston toad was listed as an Endangered Species, and a recovery plan was created. Its goal is the removal of A. houstonensis from the endangered species list through habitat expansion and enhancement.

Contributors

Nathan Fostey (author), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

References

BROWN, LAUREN E., AND ROBERT A. THOMAS. 1982. Misconceptions about the endangered Houston toad (Bufo houstonensis). Herpetological Review 13(2): 37.

HILLIS, D. M., A. M. HILLIS, AND R. F. MARTIN. 1984. Reproductive ecology and hybridization of the endangered Houston toad (Bufo houstonensis). Journal of Herpetology 18(1): 56-72.

JACOBSON, N. L. Breeding dynamics of the Houston toad. 1989. Southwestern Naturalist 34(3): 374-380.

MAYS, S. R. AND P. S. FREED. 1985. Bufo houstonensis (Houston toad) coloration. Herpetological Review 16(4): 108-109.

THOMAS, L. A. AND J. ALLEN. 1997. Bufo houstonensis (Houston toad) behavior. Herpetological Review 28(1): 40-41.

U.S. FISH AND WILDLIFE SERVICE. 1984. Houston toad recovery plan. U.S. Fish and Wildlife Service, Albuquerque, New Mexico 73pp.+iii

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