Even though there are thousands of endangered species, zoos have only been able to return about 16 species to the wild with varying level of success. Most zoo animals released in the wild don't survive. This is because zoos don't provide the right environment for a successful captive breeding project. The animals would need to live in habitats resembling their natural ones, especially in terms of climate and fauna. The animals would also need to be raised with minimal human contact and in populations large enough to provide a natural social balance and a suitable gene pool.