There are also dangers attached to attempts to re-introduce animals to the wild. In the wild, species build an immunity to naturally occurring disease, but in a zoo they might not develop resistance to the most commonplace of ailments. Instead they may be challenged by viruses from an animal that they would never otherwise meet. Viruses can mutate or be transferred across the globe to devastate wildlife. In 1991, a lethal virus was identified in a zoo-bred tamarin just 3 days before the animal was to be released into an area where the virus was unknown.
Zoos also claim to be educational.
Animals which have become depressed or show unnatural stereotypic behaviour are only 'educational' in showing how man can drive an animal mad by keeping it in unnatural prison-like conditions. Wildlife films which show how animals behave naturally have done far more to promote respect for animals. Studying the natural behaviour of animals in captivity will rarely give accurate information. In many cases, zoo animals are bred to attract visitors and publicity, and to make a profit. Certain safari parks and zoos have admitted culling surplus monkeys and supplying animals for experimentation or collaborating with animal researchers.