Tuesday, April 18, 2006

The many lives of the black-footed ferret

Black Footed Ferret
The Times has a story today describing the latest threat to the black-footed ferret, Mustela nigripes.
The ferrets feed principally on prairie dogs, and the rodents are a reservoir for plague bacteria, and the highly endangered ferrets turn out to be very susceptible to plague. The infection is gradually spreading as infected fleas spread north toward the major concentration of wild ferrets in South Dakota.

The history of ferret conservation is actually more complex than what the TImes presents. In the '70s, what were believed to be the last wild ferrets were brought to Maryland to be part of a captive breeding program. As a routine precaution, they were given a canine distemper vaccine.

Turns out that the ferret immune system wasn't ready for even an attenuated distemper vaccine, and the lot of them were soon dead, infected and killed by the vaccine meant to save them (Carpenter, 1976).

At that point, people thought that black-footed ferrets were gone from the world, a victim of competition between cows and prairie dogs. Cows had farmers and the federal government behind them, so the prairie dogs went from huge populations to scattered colonies. WIthout the prey density to support themselves, the ferrets seemed to have disappeared.

A rancher's dog killed a ferret a few years later, and scientists rushed in, hoping to find another population.

With a little more care, the captive population grew, and wild populations were re-established several years later. Now the populations are threatened by a disease sweeping through their prey. There are lots of paths to extinction for a species that's gone to such a low population, and there may be no path away. We can hope that the species has a few more lives left in it.

Carpenter, J., et al, (1976) "Fatal vaccine-induced canine distemper virus infection in black-footed ferrets," J. Am. Vet. Med. Assoc.,.169(9):961-4.