Within the next decades species extinction may eliminate between 20 and 50% of the Earth's species. Captive breeding has often been claimed to be a useful tool in preservation of biodiversity. The role of zoos in conservation work and the value of captive breeding are discussed; the latter exemplified by the Peregrine Falcon (Fal¢o peregrinus) Programme and the Arabian oryx (Oryx leucoryx) Programme. Captive breeding programmes are very resource demanding and can only be afforded for a very small number of species, which limits their value significantly.
Zoos deal mainly with vertebrates, but these comprise less than 3% of the described species, and although the 878 zoos considered hold more than 20 000 specimens of 140 threatened mammal species, they probably only contribute to the conservation of 20 full species. The situation for birds, reptiles and amphibians is even worse. Zoos face serious problems with minimum viable population sizes and hybridization. However, zoos can make a major contribution to preservation of biodiversity through educating and informing the public. Today, where the crisis of extinction of species has reached such daunting dimensions, captive breeding and other ex situ conservation tools should be the last resort for preserving biodiversity, and captive breeding must not become an excuse to avoid dealing with preservation of habitats.