Conservationists are anxious to re-establish populations of endangered species in the wild whenever suitable habitat becomes available. Many zoos, worldwide, are committed to breeding and maintaining viable stocks of endangered animals to ensure that species which are becoming increasingly rare in the wild have a residual population in captivity. The logic underlying this approach is that captive bred stocks can be re-introduced to supplement wild stock or, in the worst case, actually to form a new population in the wild.