Wyoming Toad

Bufo hemiophrys baxteri

Description

The Wyoming toad, the only toad in the Laramie Basin, is a small bufonid about 2 in (5 cm) long with crests on the head that form a humped ridge. Light brown with dark blotches, the body is covered with many warts.

The Canadian toad (Bufo hemiophrys hemiophrys ), a closely related species, occurs in Manitoba, Alberta, Saskatchewan, Minnesota, Montana, and the Dakotas. Some scientists argue that the Wyoming toad is a full species, rather than a subspecies. Further research is needed to determine this toad's precise taxonomic classification.

Behavior

The tadpole of the Wyoming toad feeds primarily on plant matter, but the full-grown toad preys on insects, larvae, and any small organism that moves. Because of poor eyesight, the toad tends to miss motionless prey. The female discharges eggs in strips of jelly in standing pools. The male clings to her back and fertilizes the eggs as they reach the water. Tadpoles hatch between three and 20 days later, depending on the water temperature, and begin to metamorphose. The toad develops hind limbs first, then front limbs; as the lungs develop, its tail gets shorter and gradually disappears.

Habitat

This species is found in wetlands adjacent to the Laramie River in the Laramie Basin. It is strongly aquatic, spending most of its time in and around water.

Distribution

The Wyoming toad was once common in the Laramie River basin in southeastern Wyoming and probably inhabited similar marshy habitats in other parts of the state. Fossils found throughout the region suggest that the species was abundant thousands of years ago. Researchers from the University of Wyoming have monitored breeding sites annually since 1945 and became alarmed when their 1978 and 1979 surveys found very few toads.

In 1980 the University of Wyoming and the U.S. Fish and Wildlife Service (FWS) conducted an extensive survey of the Laramie Basin. A single population of the toad was located on private land in Albany County, where a number of males were heard calling, but no females, tadpoles, or eggs were found. The 40-acre (16-hectare) site was thought to support about 25 individuals. A survey of this site in 1983 revealed only two toads, and in the following year, none.

In 1987, a new population was discovered on private land in Albany County, which considerably brightens the Wyoming toad's chances for survival. The new site—about 10 mi (16 km) west of Laramie—is home to about 200 toads, which scientists consider a fairly good breeding population.

Threats

The reasons for the toad's basin-wide disappearance are not understood, but the leopard frog (Rana pipiens ), once fairly common, has also disappeared from the Laramie Basin. Scientists believe that the decline of both toads may be linked with herbicide application. Herbicides have been used by the Wyoming Department of Agriculture for weed control in roadside ponds and along field edges typically used by the Wyoming toad. Regional aerial application of Baytex (Fenthion) with diesel fuel began in 1975 to kill mosquitoes. The combination of Baytex and diesel fuel is highly toxic to toads and frogs. Predation may also be a factor in the sudden decline of the Wyoming toad. The California gull has become more numerous in recent years. Local ranchers report that fields are sometimes "white with gulls" in early spring when toads are breeding. Other predators, such as raccoons, foxes, and skunks have all increased in number.

Conservation and Recovery

By 1994 the Wyoming Game and Fish Department had brought into captivity the last known wild Wyoming toad populations in an effort to prevent the species from becoming extinct. The Wyoming Game and Fish Department, along with the FWS, started the Wyoming Toad Recovery program. Three zoos—Cheyenne Mountain Zoological Park, Omaha's Henry Doorly Zoo, and Toledo Zoological Gardens—received tadpoles and toads.

The recovery efforts have not always gone smoothly. There are a number of husbandry issues, including climate simulation and diet, that have to be resolved in order to prevent the loss of the captive populations. The toads also are very susceptible to "red leg", a bacterial infection, which has been one of the leading causes of death. Experts from zoos have been advising the various government agencies in their efforts to improve the husbandry techniques and discover the underlying factors involved with the high incidence of red leg. This husbandry advice from zoo professionals has led to a dramatic decrease in the mortality rate, dropping from around 50% to less than 10%.

Zoos have also had a great impact on the captive breeding of the Wyoming toad. They studied the breeding season of the toads and discovered several factors that need to be present in order to greatly increase the chances of successful breeding. They have worked with the government officials to determine the effects of male and female hibernation on reproduction. Zoos have also shown others involved in the recovery program how to use synthetic hormones to induce the toads to lay eggs.

As a result of the improved breeding and husbandry techniques, the captive population greatly increased in 1995, allowing many animals to be released back into the wild. To increase their chances for survival, the tadpoles were placed in head start tanks at the release sites. These are wading pools, covered with screen, that house tadpoles and toadlets. Tadpoles and toadlets have separate tanks, allowing for the different needs. The tanks are checked regularly to remove toadlets from the tad-pole tank and to make sure that the toadlets are not able to escape through gaps between the screen and the pool wall. Measures have also been taken at the release sites to protect the tanks from grazing cattle and to biologically control the mosquito populations without pesticides. During the summer months, tadpoles and toadlets were released at three different lakes in the Laramie area: Lake George, Rush Lake, and Mortenson Lake. These sites will be monitored closely over the next few years to see if Wyoming toads are able to reestablish their place in the wild.

Contact

U.S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
P.O. Box 25486
Denver Federal Center
Denver, Colorado 80225
http://www.r6.fws.gov/

References

Baxter, G. T., and M. Stone. 1980. "Amphibians and Reptiles of Wyoming." Wyoming Game and Fish Department Bulletin, Laramie.

Porter, K. P. 1968. "Evolutionary Status of a Relict Population of Bufo hemiophrys Cope." Evolution 22: 583-594.

Swaringen, Karen. March 1996. American Zoological Association. "AZA Conservation Spotlight."