Because black-footed ferrets eat prairie dogs [1] and live in their burrows, they are completely dependent upon large prairie dog colonies for survival. But prairie dog colonies have been reduced to less than 5% of the area they originally occupied due to habitat destruction [2], poisoning, shooting, and exotic disease (sylvatic plague). The remaining colonies are relatively small and fragmented, and often separated by great distances. With the dramatic loss of prairie dogs came the loss of almost all black-footed ferrets as well. In fact, by 1986 only 18 black-footed ferrets remained.