Animal Reintroduction

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Natural-resource management uses animal reintroduction for the following two purposes: to restore balance to a damaged ecosystem and to return an endangered species to the wild. In many cases a reintroduced species can turn the tide on invasion, especially when eradication gives only partial success. Rather than put effort into eradicating difficult invaders, biologists can reintroduce animals that can restore balance to the ecosystem.

Reintroduction is done by either relocating animals from another community where their population is dense or by releasing them from breeding-in-captivity programs. Each method requires careful management of the animals during their capture, transport, and release. Reintroduction programs are more than trucking a group of animals to the wild
and opening their cages. Many animal advocates have concerns about reintroduction because they believe the process puts too much stress on both the released animals and the native species that have learned to live in their habitat without the added competition. Other critics fear for the safety of people, pets, and domesticated animals. The following case study on the return of gray wolves to Yellowstone National Park sheds light on this controversy.

Wildlife biologists develop a thorough understanding of the habitat before reintroducing any animal. Captivity breeding programs such as that run by many zoos have programs that prepare animals for release and ensure the best results for all members of the natural community. The Association of Zoos and Aquariums provides guidelines on the best
ways for carrying out a reintroduction that is successful both for the reintroduced animal and for the habitat’s existing species. According to the guidelines, a reintroduction should satisfy the following conditions:

1. aid a native population that can be self-sustaining once it is in the environment
2. preserve the existing ecosystem
3. take place in the animal’s normal habitat
4. take place in an area of the animal’s normal distribution
5. occur only in habitats not threatened by destruction
6. protect the reintroduced animal from aggression from animals in the habitat
7. not be a solution for disposing of surplus captive animals and orphans
8. not threaten the survival of species already living in the habitat

Mentor animals that live in captivity also help by teaching other members of their species about finding food and avoiding predators. Handlers teach young birds how to avoid power lines, and all activities at the training center try to minimize any connections a wild animal might develop
with humans.

Ideal reintroduction habitat should be free of overhunting, land development, fragmentation, pollution, exotic predators, or diseases that could infect the reintroduced species. Large animals such as wolves usually enter in numbers of 50 to 150 to help them build a social structure. Biologists furthermore try to release animals that are similar, genetically and physically, to the natural populations that once lived in the area. Veterinarians meanwhile make sure the animals are healthy and have no injuries; they are vaccinated before their release. Animals with infirmities or behavioral problems do not qualify for release in order to prevent them from being harmed in the wild.

Transport should involve as little noise and other stress as possible. Biologists prepare mammals for release by holding the animals in pens for a period of time at the release site. This acclimation period gives the animals time to overcome any stress caused by the trip, adjust to climate, recognize landmarks, and develop relationships in their group. Biologists provide food for certain released species, such as condors, to help their transition into new surroundings, while other species, such as wolves, simply leave their enclosure to begin their new life in the wild. Many reintroduced animals have transmitters attached to them so scientists can monitor them by radiotelemetry and learn about their behavior.

Even after all these precautions, animal reintroductions can be a tense time for biologists because no one can be certain of the success or failure of animals they have trained and come to know. Geneticist Hans Peter Koelewijn of the Netherlands summed it up this way at a conference on
wildlife reintroduction in 2008: “You can have a technical strategy, a scientific strategy, and a socioeconomic strategy, but the animals also have their own strategy.” Biology contains very few absolutes.