Amphibian Conservation: Wyoming Toads Prepare for Breeding

A pair of small gold eyes peers out from under a mass of sphagnum moss. In a day or two, this warty creature will complete its climb out from the depths of the sandy soil where he has spent the last 30 days sleeping and “chilling” at a cool 38 degrees. Along with seven other individuals of this species, he will awaken due to an increase in temperature and light. By the time the temperature reaches 74 degrees, he will have completely removed himself from the soil and be sitting atop it, hopefully alongside his companion, a slightly larger female. In the week that follows, events these two small cold-blooded creatures will go through could lead to producing thousands of their species in a matter of hours due to their “explosive” nature.

The Wyoming toad (Anaxyrus baxteri) is one of North America’s most endangered species and one of the amphibians we work with as part of a Species Survival Plan (SSP) at the Detroit Zoo’s National Amphibian Conservation Center.  This toad’s wild populations began declining in the 1970s, and by the 1980s was listed as an Endangered Species by the International Union for the Conservation of Nature (IUCN). Possible causes for the population decline are use of aerial pesticides to eliminate mosquitoes, habitat manipulation, and disease in the form of the amphibian chytrid fungus. Realizing a decline was occurring, the last remaining toads were collected and by 1994, all remaining wild-born Wyoming toads were believed to be entirely in captivity. The IUCN now describes the Wyoming toad as extinct in the wild, meaning any toad currently found in the wild has come from captive breeding, in which the Detroit Zoological Society (DZS) has been actively involved.

The Wyoming toad SSP is managed by the Association of Zoos and Aquariums (AZA). The DZS has been a member of this conservation program since 1995 and since 2001 has sent a total of 6,505 tadpoles and toadlets to the wild. All Wyoming toads are the responsibility of the U.S. Fish and Wildlife Service (USFWS), so members of the AZA work closely with them to follow all USFWS permit guidelines for keeping them in captivity. The goal of any captive breeding program is to produce healthy offspring for release into the wild with the goal of rebuilding them into a self-sustaining population. Each toad in captivity is identified and tracked, which helps to pair toads that will produce the most genetically diverse and healthy offspring. Breeding pairs of toads are chosen almost a year in advance so toads have plenty of time to move from one zoo to another to create the breeding pairs.

Although not as well known as Jabari and Kivuli, the giraffe couple at the Detroit Zoo, Wyoming toads Butler and Beverly are a very important couple of toads. They are part of a “bio-secure” population and will never be seen by the public, which ensures they will not accidentally release diseases, known or unknown, into the wild via their offspring. They are held with four other pairs of Wyoming toads in a special room away from all other amphibians, so they will remain free of diseases that could otherwise be found in species not native to the western region of North America.

At the AZA’s recommendation, Butler arrived at the Detroit Zoo last October to be paired with Beverly, who arrived in 2012. Both are now 3 years old, which is about middle aged for a Wyoming toad. In early April, they were placed together into a thermostat-controlled “hibernaculum”, which is used to cool the toads, simulating the hibernation period a wild Wyoming toad would go through during the winter. The toads are kept cooled for about a month to help prepare them for breeding; eggs or sperms may develop and mature as a result of this cooling. The toads are given plenty of sandy soil to bury down into and sleep in just as they would have in the wild, and the Zoo’s animal care staff checks in on them weekly to make sure they are doing well.

At the end of May, the temperature in the hibernaculum will be increased to 70 degrees Fahrenheit and the toads will begin to awaken. Once they have climbed out from the soil, we will place them back into regular husbandry for a few days where they will continue to warm up and eat. Recordings of male toads calling are played during this time to condition toads further for breeding. Within a few days of emerging from hibernation, Butler and Beverly will be placed into a breeding chamber with 2-3 inches of water. The pair will hopefully go into “amplexus” within a few hours, which happens when the male positions himself on top of the female using his front legs and squeezes her, encouraging her to lay eggs. He fertilizes the eggs as she lays them, usually in the dark, overnight. Butler and Beverly should lay thousands of eggs, which is typical of toad species. Described as “explosive breeders”, the more eggs they can lay the better the chance offspring have of surviving the elements, diseases and predators. Since this is a captive breeding, we can help the thousands of eggs that Butler and Beverly produce survive into strong, healthy tadpoles.

Approximately two to three weeks after eggs have hatched into thousands of hungry tadpoles, arrangements are made with the USFWS to ship the tadpoles to Wyoming, where they will be released into protected wetlands. These tadpoles will add to those previously produced in captivity sent yearly by the zoos that participate in this program and the USFWS.

The wetlands are monitored during the spring and summer as part of yearly field surveys done to track the health and population of the toads. This year we hope that Butler, Beverly and the three other pairs of Wyoming toads at the Detroit Zoo are able to contribute thousands of healthy tadpoles to the wild population.

– Rebecca Johnson is the associate curator of amphibians for the Detroit Zoological Society.

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