It is the same story for the European bison, which was limited to just a few zoos before re-introduction programs across eastern Europe helped re-build the population to current levels of around 1, 800.

CNN: All creatures great, small and disappearing

"The fate of the European bison provides an example of the way in which a species may be brought to the brink of extinction in a very short time, and then saved only through great efforts, " says Dr. Zbigniew Krasinski of Poland's Bialowieza National Park.

CNN: All creatures great, small and disappearing