Modern zoos are increasingly successful in maintaining and breeding exotic species. Many of the animals bred in captivity cannot be housed in their natal zoo nor in other recognized zoos in the region. These 'surplus' animals create a problem as zoos only have limited space at their
disposal. The options open in this situation are to avoid the problem by preventing the animals from breeding (sterilization or contraception) or to dispose of the surplus animals (euthanasia; or transfer either to institutions not recognized by airy national zoo federation or to a zoo outside
the region, possibly using the services of an animal dealer). The pros and cons of all these options are evaluated in terms of practicality, welfare and ethics. In many cases, the judicious use of a combination of contraception and euthanasia would seem the most acceptable choice from an animal
welfare point of view. Nevertheless, it is believed that considerably more research is needed into the methods and welfare aspects of contraception and sterilization.