Official estimates are that just 3,000 – 4,000 adult Houston toads are left in the world.
The Houston toad (Bufo houstonensis) is an endangered species of amphibian that is endemic to Texas in the United States. This toad was discovered in the late 1940s and named in 1953.
The Houston toad is 2 to 3.5 inches long. Its general coloration varies from light brown to gray or purplish gray, sometimes with green patches. The pale undersides often have small, dark spots. Males have a dark throat, which appears bluish when distended.
The Houston toad today lives exclusively in pine and oak woodlands and savanna with forbs and bunchgrasses present in open areas. Vegetation of its preferred habitat includes loblolly pine (Pinus taeda), post oak (Quercus stellata), bluejack oak (Quercus incana), yaupon holly (Ilex vomitoria), curly threeawn (Aristida desmantha), and little bluestem (Schizachyrium scoparium). They are generally found in areas with loose, sandy soils greater than 40 in (100 cm) in depth. Slow-moving or still bodies of water that last at least 30 days are needed for breeding and tadpole development. The toad's original range covered 12 counties in Texas; currently, it is often reported to occur in nine counties. However, choruses have only been actually reported in three counties since 2000, representing a seventy-five percent overall reduction in twenty years.
Though the largest and most immediate threat is habitat loss, the reduced toad populations are also vulnerable to automobiles, predators, pesticides and drought.
Habitat loss and alteration are the most serious threats facing the Houston Toad. Alteration of ephemeral and permanent natural wetlands for urban and agricultural uses eliminates breeding sites. Draining a wetland, or converting an ephemeral wetland to a permanent pond, can eventually cause the Houston toad to decline or be eliminated entirely. Conversion to permanent water not only makes them more vulnerable to predation by snakes, fish, and other predators; but also increases competition and hybridization with closely related species.
Periodic drought is also a threat, particularly long-term drought such as that experienced during the 1950's. Drought may result in the loss or reduction of breeding sites as well as enhanced mortality of toadlets and adults.
Extensive clearing of native vegetation near breeding ponds and on the uplands adjacent to these ponds reduces the quality of breeding, foraging, and resting habitat, and increases the chances of predation and hybridization. Conversion of native grassland and woodland savannah to sod-forming introduced grasses, such as bermudagrass and bahiagrass, eliminates habitat because grass growth is generally too dense for the toad to move freely. Dense sod also inhibits burrowing.
High traffic roads are a barrier to Houston Toad movement, and toads are sometimes killed on roads. Other linear features such as pipelines and transmission lines can create barriers between foraging, hibernating, and breeding sites, especially if native vegetation has been removed.
The Houston toad lives primarily on land.
The toads burrow into the sand for protection from cold weather in the winter (hibernation) and hot, dry conditions in the summer (aestivation). Plants that are often present in Houston toad habitat include loblolly pine, post oak, bluejack or sandjack oak, yaupon, and little bluestem.
For breeding, including egg and tadpole development, Houston toads also require still or slow-flowing bodies of water that persist for at least 30 days. These water sources may include ephemeral (temporary) rain pools, flooded fields, blocked drainages of upper creek reaches, wet areas associated with seeps or springs, or more permanent ponds containing shallow water. The toads do best in ponds without predatory fish.
The Houston toad is a year-round resident where found, although its presence can most easily be detected during the breeding season, when males may be heard calling. Males usually call in or near shallow water or from small mounds of soil or grass surrounded by water. Males occasionally call from wooded habitat located within about a 100-yard radius of breeding ponds. The call is a high clear trill that lasts an average of 14 seconds. The call is much like that of the American toad (Bufo americanus), but ususally slightly higher in pitch. The American toad occurs in Texas, but north of the range of the Houston toad.
Houston toads may call from December through June. Most breeding activity takes place in February and March, and is stimulated by warm evenings and high humidity. Toads emerge from hibernation to breed only if moisture and temperature conditions are favorable. Males call females to the breeding pond with a high, clear trill. Females, responding to calling males, move toward the water to mate. The female lays her eggs as long strings in the water, where they are fertilized by the male as they are laid. The eggs hatch within seven days and tadpoles metamorphose (turn into toadlets) between 15 and 100 days, depending on the water temperature.
Young toadlets are about one-half inch long when they complete metamorphosis. They then leave the pond and spend their time feeding and growing in preparation for the next breeding season. Males generally breed when they are a year old, but females may not breed until they are two years old. Houston toads, especially first-year toadlets and juveniles, are active year round under suitable temperature and moisture conditions. Their diet consists mainly of insects and other invertebrates. They live 2 to 3 years.