Back From the Brink

Is Captive Breeding Creating Viable Populations…Or Zoo Specimens?

Captive breeding of an endangered species can make the difference between its success or failure. The black-footed ferret, the cheetah, the Wyoming toad and the peregrine falcon have all spent generations in captivity, where they eat, drink, sleep and mate at the direction of biologists. All four have teetered on the edge of extinction but, at least partly as a payoff for “doing time” in captivity, they’ve dodged the bullet for now.

According to Dr. E. Tom Thorne of the Wyoming Game and Fish Department Research Unit in Laramie, Wyoming, captive breeding of the black-footed ferret was “biologically mandatory” if they were to recover from disease and the decimation of their habitat and food supply. Thorne is the veterinarian in charge of the ferret captive breeding program developed to help the animal flourish again in the wild.

The black-footed ferret is the only wild example of the genus in North America. It was thought to be extinct until 1981, when a sheepdog surprised wildlife biologists by killing one on a ranch in northwestern Wyoming. Then the chase was on to locate, collar and study the species. The sole surviving colony was discovered in a nearby prairie dog town (whose inhabitants make up close to 90 percent of the ferrets’ diet).

The loss of prairie dog towns, caused in great part by farmers and ranchers who consider them a threat to cattle operations, harmed the prairie ecosystem and severely reduced the ferret population. Also, prairie dogs—which carry sylvatic plague and canine distemper—transmitted it to the ferrets, and caused large losses. In 1984, there were 129 ferrets in the Wyoming colony. In 1985, a sylvatic plague outbreak caused the number to drop to 58. After efforts to control the plague failed, the population was moved to a Wyoming Game and Fish research unit.

Since then, efforts to breed and release captive-bred ferrets into the wild have been going well. Careful mating has retained 80 percent of wild genetic diversity, and the population expanded to seven zoos nationwide, so that a calamity at one location would not wipe out the species. By 1992, a total of 349 ferrets were being held in locations across the country, and nearly 100 were released into the wild in Wyoming, Montana and South Dakota.

Scientists believe that ferrets have a bright future because every year they have been released into the wild, they have bred. But because of Wyoming Game and Fish budget woes, the program will soon be turned over to the U.S. Fish and Wildlife Service. Thorne is concerned that the federal agency will have difficulty running the large-scale operation without state partnerships. He is also concerned that federal funding for non-game animals is in short supply, and that the ferret will not get proper attention.

Wyoming is also the home of the Wyoming toad, which was known to exist only in one small area. To protect it, captive breeding began, and the Environmental Protection Agency (EPA) issued restrictions on the use of 42 pesticides and chemicals in a 100-square-mile radius. Meanwhile, farmers worried that mosquitoes would bring misery to themselves and disease to their livestock formed a task force to protect scheduled malathion spraying. Ultimately, ranchers, environmentalists, biologists and politicians joined together in an effort to find common ground. In a compromise, the EPA lifted its ban on pesticide use, and the residents and ranchers agreed to use a reduced-strength mosquito spray. Meanwhile, the toads are doing well in captive breeding.

Some breeding experiments involve international travel. New Mexico’s Rio Grande Zoo had a new addition in November: a female cheetah cub named Esperanza. Here’s the catch: The cub’s parents live on different continents, and have never met.

“The cub is the first surviving offspring of an endangered species to be conceived using intercontinentally transported cryo-preserved sperm,” says Dr. Michael Hutchins, director of Conservation and Science for the American Zoo and Aquarium Association (AZA), based in Washington, D.C. Sabie, the cub’s mother, was artificially inseminated with sperm collected from a wild male cheetah in Namibia. Frozen using liquid nitrogen, the sperm was then transported to the Rio Grande Zoo, where artificial insemination (AI) took place.

The cub was not only the first endangered animal to survive this special technique; she was also the result of a 10-year collaboration among scientists from 35 countries to develop survival plans for over 100 animals using AI technology. Cheetahs, known for their speed and agility, have not traditionally bred well in captivity. Because of their somewhat closed population in American zoos (324 scattered among 49 institutions) genetic diversity has remained a hindrance to recovery.

“The cheetah won’t breed naturally in lots of cases, so AI has to step in,” says Jennifer Buff, a bio-technician with the New Opportunities in Animal Health Science (NOAHS) reproductive group. “In dealing with captive populations, one has to realize that cheetahs suffer an incredible mortality rate in the wild, from predation, disease and hunting.”

The AI concept is also being tried on several other threatened and endangered species, including the domestic ferret, tiger, puma, clouded and snow leopard and ocelot.

Captive breeding has been a tremendous success in the case of the Peregrine falcon. With 39 known pairs in the west and none in the east, 1975 was not a good year for the raptor. But when the cause of the bird’s decline was discovered to be a chemical in DDT, the pesticide was banned. The ban, along with captive breeding by the Peregrine Fund, has brought the bird back to viable numbers. They have recently been “downlisted” from endangered to protected, says Nancy Frueutel, the Peregrine Fund’s education director. The release of captive-raised birds has brought the species back to an encouraging 828 pairs in the west, 62 pairs in the midwest and Central Canada, and 104 pairs in the east.

The Washington-based conservation group Defenders of Wildlife (DOW) is concerned that animals bred in captivity may be released in areas as harmful to them as the environment they came from. Heather Weiner, a DOW legislative counsel, says that unless an animal bred in captivity can be returned to a safe environment, these programs create “zoo specimens” that won’t survive genetic downgrades.

Captive breeding is not the ideal solution, obviously, but to increasingly beleaguered conservationists, it’s looking like the only solution.