The Houston toad (Bufo houstonensis) was the first amphibian granted protection under the U.S. Endangered Species Act. Critical habitat was designated in Bastrop and Burleson counties in 1978, in areas supporting the largest populations known at that time. Primary threats to this species’ survival are habitat modification and fragmentation, vehicular traffic, predation, and prolonged drought. To that list we may soon need to add chytridiomycosis, a fungal disease that is decimating Central American amphibian populations and has now been reported in wild populations of the Barton Creek salamander (Eurycea sosorum) in the Colorado River watershed.
Nearly 30 years ago, at the same time that the State of Texas acquired critical Houston toad habitat in Bastrop County adjacent to Buescher and Bastrop state parks, the Houston Zoo initiated a captive breeding program to help supplement remaining populations or establish new ones in protected areas. However, in spite of introducing 62 adults, 6,985 newly metamorphosed toads, and 401,384 eggs at 10 sites within the Attwater Prairie Chicken National Wildlife Refuge over a five-year period (1982-1986), it was not possible to establish a viable population at that site.
Historically, the Houston toad ranged across the state’s central coastal region, but disappeared from Harris and Fort Bend counties in the 1960s following an extended drought and Houston’s urban expansion. Although this species has been found in nine additional counties (Austin, Bastrop, Burleson, Colorado, Lavaca, Lee, Leon, Milam, and Robertson) as recently as the 1990s, several of these populations have not been detected since their discovery. In 2006, the species was heard calling only in Bastrop and Leon counties; in Leon only a single male was located. Bastrop County is the species’ final stronghold, but studies also suggest its population is in decline.
In the spring of 2007, the Houston Zoo received partial egg strands from the Bastrop County population collected by Texas State University. Houston Toads were brought into captivity for four reasons. The first is as a safe guard or “assurance population” against a catastrophic event that might cause the Houston Toad to go extinct in the wild. If this happens, Toads in captivity will serve as a source for individuals for reintroductions. The second reason is that in the 1984 USFWS Recovery Plan, a conservation stragegy recommended was the reintroduction of toads into appropriate habitat. It is hoped the captive toads will serve as a source for individuals who might be reintroduced into historical localities. The third reason is for head starting. Head starting is a process where high-mortality life stages (such as larval and juvenile in amphibians) are protected and released after they had reached a certain size or life stage. This technique has proved helpful in the recovery of other endangered species. The fourth and final reason is research. Toads can be very difficult to find in the wild, even during the breeding season. With toads in captivity we can study various aspects of their natural history and biology, such as activity temperatures, burrowing abilities, and substrate preferences that are very difficult to study in the wild. The eggs hatched and about 1,500 toads completed metamorphosis. We performed three releases in 2007 (May, July, and September) and another in April 2008. About 1,200 toads were released in total and we look forward to seeing the results of this work in the coming years. The remaining toads were kept at the zoo to start the formation of our assurance colony.
