Captive breeding programs have been used in an effort to preserve species that are endangered. However, there are many problems that arise. For example, if the species are highly mobile or migrate, as in many fish, birds and others, it may pose a problem if the species is used to traveling to a breeding ground. Also, if habitat destruction has occurred, once the species are released to the wild, there may not be enough habitat to support them in terms of food and space. Inbreeding can become a problem especially in zoos or aquaria as there may be a very limited gene pool in such a small population. Random breeding in the wild leads to a healthier population with a greater variety of genes in the offspring. Many countries participate in captive breeding programs to try to preserve the biodiversity of species on Earth.