Captive breeding and reintroduction

In recent years ex situ conservation efforts have become increasingly important. Zoos, botanical gardens, wildlife parks, and conservation trusts now work in collaboration to maintain captive assurance colonies of threatened plants and animals. Studbooks on target species are kept by participating institutions, and breedings are scheduled in consultation with conservation geneticists.

The proximate mission of ex situ colonies is to maximize genetic diversity within a captive population of affordable size. Long-term, however, the fundamental conservation goals of captive breeding are release-in-habitat with the skills necessary for survival—and eventual reestablishment of viable wild populations within target species' historical ranges. Captive propagation definitely works, and more threatened species are now bred in zoos, etc., than ever before. On the other hand, reintroductions (as well as related programs such as translocation of wild animals) have enjoyed only mixed success.

The case of the giant panda (Ailuropoda melanoleuca) may be instructive. Today only about 1,000 of these magnificent animals survive in the mountain forests of central China. Years of environmental degradation, disease, and depredation have taken their toll on A. melanoleuca. Furthermore, within the animals' fragmented habitat, post-flowering bamboo die-offs have added malnutrition to the pandas' tale of woe. Presently, about 140 giant pandas are maintained in Chinese zoos and in other breeding facilities around the world. However, despite the infusion of massive amounts of money, captive breeding programs have met with only limited success. Of the 226 giant pandas born in captivity between 1963 and 1998, only 52% survived for as long as a month, and others died before they reached reproductive maturity. At present the captive population is scarcely self-sustaining, and it may not produce appreciable numbers for release within the foreseeable future.

By contrast, captive propagation and reintroduction have been more successful with the golden lion tamarin (Leontop-ithecus rosalia), a small primate endemic to the Atlantic coastal forests of eastern Brazil. Because of over-exploitation and (particularly) habitat destruction, this tamarin had become endangered by the late to mid twentieth century. Beginning in 1984, scientists from Brazil and the United States began rein-troducing zoo-born golden lion tamarins back into their habitat in the wild—primarily onto private lands that could be protected against the ravages of timber harvest. The combined efforts of governments, nongovernmental organizations (NGOs), local communities, zoological parks, and conservation scientists have more than doubled the size of the wild golden lion tamarin population.

A review of 116 reintroductions (89 involved mammals; all were carried out between 1980 and 2000) concluded that 26% succeeded and 27% failed. (The remaining 47% were classified as uncertain.) Many factors influence reintroduction success. These include habitat quality, the number of individuals released (there is no magic number, but 100 has become the rule of thumb), and the density of predators. Before any reintroduction is attempted, however, conservationists should identify and eliminate the cause of the target species' initial decline. If this can be done, then a reintroduction has a reasonable chance of success. Otherwise, a reintroduction may provide opportunities for feel-good press releases, but it is unlikely to result in establishment of a viable wild population.

Translocation involves moving wild animals from one place to another and therefore is, in a sense, an ex situ activity. Sometimes translocations are attempted without adequate preparation. For example, in French Guiana, howler monkeys

(Alouatta seniculus) were translocated because their habitat was to be flooded by the construction of a hydroelectric dam. These individuals were moved to an area where howler numbers had been reduced by hunters—and where hunting still occurred. In other words, the cause of the original population decline had not been addressed, and the success of the translocation is still in doubt.

The translocation of Asian rhinoceroses (Rhinoceros unicornis) in Nepal is a happier story. Nepali government biologists, assisted by World Wildlife Fund for Nature (WWF), U.S. Fish and Wildlife Service (USFWS), and the King Mahen-dra Trust, captured rhinos in Royal Chitwan National Park and transported them 220 mi (350 km) cross-country to Royal Bardia National Park. The receiving park was within the Asian rhino's historic range. Habitat was excellent (in quality and quantity), and although R. unicornis had been extirpated from Bardia by poachers, the park was well protected by the time the reintroduction project began. Rhino translocations have continued for a decade, and now conservation biologists believe that Nepal has successfully established a second viable population of R. unicornis.

Translocations of wild animals are often attempted for reasons unrelated to conservation. While conservationists may not generally support the movement of wildlife to solve human-animal conflicts, they can sometimes learn valuable lessons from such activities. For example, nuisance brushtail possums (Trichosuros vulpecula) moved from the city of Melbourne into the Australian outback suffered heavy depredation. Similarly, small, endangered mammals, raised in a zoo, might require some sort of predator-avoidance training before they were released into areas with high predator densities. White-tailed deer (Odocoileus virginianus), captured for translocation when the Florida Everglades were in flood, generally did not survive the ordeal. From this experience some biologists learned a great deal about the importance of minimizing capture-trauma when dealing with mammals already under severe stress. Translocations of nuisance raccoons (Pro-cyon spp.) and black bears (Ursus americanus), though perhaps unwise, reinforce the lesson that some animals know how to get home—and will walk a very long way to get there.

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