Captive Breeding and Reintroduction

If a successful reintroduction of an endangered species is to occur, the factors causing its decline must be understood and managed. The most common cause of endangerment is habitat destruction or degradation. Obviously, it is crucial that the habitat of endangered species is conserved before captive-bred individuals are released into the wild. This is not necessarily an easily attained goal, because the causes of habitat destruction usually involve complex social, cultural, and economic factors. Controversy has, for example, accompanied reintroduction of the critically endangered California condor to the wild. The condor is a large scavenging bird that requires an extremely large range to survive, exceeding millions of acres per bird. Initially, the U.S. Fish and Wildlife Service failed to conserve enough habitat to support the highly endangered condor, resulting in controversy over the ultimate goal and likely success of the captive-breeding program. In 1986, however, an extremely large tract of suitable land was purchased for use as the base of the reintroduction of captive-reared birds, which has since begun.

After release, captive-reared animals must be monitored to determine whether they have been able to survive the stresses of living in a wild habitat. To ease the transition from captivity to the wild, the release may be somewhat gradual. For example, a "soft release" may involve the provision of food at the release point until animals learn to forage on their own. Moreover, if environmental conditions become particularly stressful, such as a drought making water and food scarce, it may be necessary to intervene temporarily until conditions improve. Monitoring the released population is necessary for the assessment of survival and the causes of mortality, so that future releases can attempt to avoid such pitfalls.

Although releases of captive-bred animals has received most of the public attention, there have also been attempts to reintroduce endangered plants to the wild. Many of the same issues are involved, but plants also present unique problems due to their lack of mobility and specific microhabitat requirements for establishment and growth. For example, the immediate environment in the soil surrounding a seed must have appropriate conditions of light, water, nutrient availability, and temperature, and must be free of seed predators and fungal disease spores. Moreover, the microhabitat requirements for germination often involve a specific disturbance regime, such as fire or canopy gaps created by tree-falls. Consequently, even in native habitats, only a very small percentage of seeds produced by a given plant can germinate and establish. In a successful reintroduction program, the habitat should be managed to allow these periodic disturbances to occur. Higher success rates in germination can be achieved in a greenhouse, after which the seedlings can be transplanted into the wild. This does not, however, dismiss the necessity of managing the land for future reproduction and survival of the plant in the wild; otherwise the reintroduction effort could fail.

A study was undertaken to evaluate 79 different reintroductions of birds and mammals in the United States It was found that certain reintroduction conditions had a higher probability of success than others. The highest probability of failure occurred when the species was a large carnivore requiring an extensive range, when the animals were released into marginal habitat, and when the released individuals were reared in captivity instead of being wild-caught and released within their lifetime. Any of these circumstances require particularly close attention if the reintroduction attempt is to be successful.

Programs of captive breeding and release can be extremely expensive, and their success may be limited because of difficulties in biology, ecology, and in addressing the ultimate cause of the species decline (such as habitat loss or excessive hunting). Moreover, reintroduction efforts should always be accompanied by a program of public education. The informed public has an influence on political decisions to attempt to reverse human-induced losses of biological diversity, and to avoid such ecological damage by preventing habitat loss, overhunting, and other destructive actions.