Biology Reference
In-Depth Information
The black-footed ferret
(Mustela nigripes)
holds the dubious distinction of being the only endangered
species among North American mustelids. Weighing approximately one and a half to two and a half
pounds, this marten-sized weasel closely resembles the steppe polecat
(Mustela eversmanni)
of Euras-
ia. Mostly yellowish brown, it has a lighter face with a black mask across the eyes and forehead and
a black-tipped tail. Further, as both the common and scientific names indicate (
nigri,
black, plus
pes,
foot), all four feet are black.
All other North American members of the weasel family seem to be at least holding their own
throughout wide portions of their range, so how did this distinctively marked animal end up in such a
precarious situation? The answer, in simplest terms, is overspecialization.
Principally nocturnal, the ferrets prey very heavily, sometimes almost exclusively, on prairie dogs;
when these rodents disappear, so do the ferrets. Over a long period, several things have drastically re-
duced prairie dog numbers throughout the ferret's range.
First, much prairie was converted to agricultural uses unsuitable for prairie dog habitat. Second,
many prairie dog colonies have been eliminated by poisoning, since the rodents were considered a nuis-
ance. And third, prairie dogs began dying from sylvatic plague, which is the animal equivalent of bu-
bonic plague—the infamous Black Death of the Middle Ages.
By 1985, only eighteen live black-footed ferrets were known to exist, and it was feared that they
would die from distemper (actually, it was later found that sylvatic plague was a greater threat). At that
time, a decision was made to live-trap them and try to raise a captive population; if their numbers in-
creased greatly, it might then be possible to reintroduce some to the wild.
Fortunately the eighteen captive ferrets thrived and multiplied. As their numbers increased into the
hundreds, efforts were made to reestablish them in the wild. Some attempts have failed, but the pro-
gram has had good success in Montana and South Dakota. At present there are around 150 ferrets in the
wild and about 350 in captivity. Although those numbers are encouraging, ferret experts caution that
the future of wild populations is still very uncertain.
Besides its endangered status, the black-footed ferret is unusual in another way: together with the
least weasel, it's the only North American mustelid that doesn't have delayed implantation. It does,
however, have what is known as
stimulated ovulation.
This means that the female doesn't ovulate until
breeding by the male causes her to do so. The two to five young are born in June and disperse as adults
in August.
The U.S. Fish and Wildlife Service, under the Endangered Species Act, has done an outstanding job
of bringing the black-footed ferret back several long steps from the brink of extinction. As with some
other endangered species whose numbers are increasing, however, it's still too early to declare victory
in the effort to save this important cog in the prairie ecosystem.
THE WOLVERINE