: San Francisco State University
The Biogeography of the Black-footed
Ferret
by Justin Bowser, student in Biogeography 316
:
Photographs courtesy of Dean Biggins
United States Fish and Wildlife Service.
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Mustelidae
Genus: Mustela
Species:
Mustela nigripes
Natural History
The black-footed ferret (Mustela
nigripes) is a member of the Mustelidae family which also contains otters, skunks,
badgers, and minks among others. It is the only native North American ferret and it
is also the most endangered north American mammal.
They are easily identified by
their black face mask, black tipped tail, and of course their black legs and feet.
On average they weigh between 1 ½ and 2 ½ pounds (Anderson et al. 1986) with the males
being larger than the females.
Over time these ferrets have evolved to become
specialized prairie dog hunters, depending on them for over 90% of their food source
(Anderson 1972). The rest of their nutrition is obtained through mice, birds and
other reptiles, and they have even been observed eating moths(Henderson et al.
1969). Black-footed ferrets have a high metabolic rate and must therefore
obtain large amounts of food in proportion to their body size. They hunt mainly at
night and they do this for two reasons: 1) they are nocturnal and 2) their prey are
larger than them and are diurnal, which means they sleep at night. With the prairie
dogs asleep the ferrets have a better chance of sneaking in and attacking the prairie dogs
before they have a chance to fight back. Black -footed ferrets prefer to make their
kills underground in the burrows but if a kill is made above ground, the ferret will drag
its prey into a burrow(Biggins et al. 1989).
Not only do ferrets rely on prairie dogs for food,
they also rely on them for their burrows which they use as a home. These homes
provide protection from predators: coyotes, owls, bobcats, foxes, badgers, hawks, eagles,
and falcons. These burrows also protect the ferrets from extreme temperatures, give
the ferrets a place to sleep and a place for the females to rear their young (Forrest et
al. 1985).
During breeding season
(March-April) male ferrets tend to roam the surrounding areas in hopes of passing on
as many of his genes as he can. Once those genes are passed on his job is
done. Approximately 41-43 days after copulation the female will give birth to a
litter, between 1 and 6, of kits (Anderson et al. 1986). The kits are born blind and
helpless and their eyes do not open for another month. They are under their mothers
care and protection for another 4 months after which time they will leave the
burrow and begin a solitary life. They reach sexual maturity at one year of
age (Anderson et al. 1986).
It is thought that the
black-footed ferrets in the wild have an average life expectancy of about 5 years with the
males living only about ½ as long as the females. In captivity, however, the life
expectancy is thought to be as high as 10 years. This is probably due to the lack of
stressors in a captive environment (U.S. Fish and Wildlife Services 1988).
Distribution
The
black-footed ferret is thought to have evolved in Europe between 3 and 4 million years ago
from weasel like ancestors. The earliest known ferret species is M.
stromeri. These ancestors were thought to have migrated to North America from
Siberia in the late Pleistocene, across the Bering land bridge. They then were
thought to have migrated southward to the great plains through ice-free passage ways
(Anderson et al. 1986). Here they met up with the prairie dogs and began evolving in
such a way that their lives became dependent on them. Although it is not’t
certain how long the black-footed ferret has been in North America, They are assumed to
have been here for over 100,000 years (Anderson et al. 1986 ). At one time the
black-footed ferrets range extended from southern Canada through the 12 Great Plains
States: Montana, Wyoming, eastern Utah, Colorado, Arizona, Texas, Oklahoma,
Nebraska, Kansas, New Mexico, North Dakota, and South Dakota, and on into northern
Mexico(Anderson 1972), (Belitsky et al. 1994). Within this range the ferrets mainly
inhabited prairie dog habitat which is primarily short grass prairies. In the last
century, however, much of this area has been found to be perfect for agriculture because
of the rich soil, and has therefore been farmed extensively. This habitat
devastation along with the mass killing of prairie dogs (also for agricultural purposes)
has limited the range of the black-footed ferrets to a few tiny populations in Wyoming,
Arizona, Montana, and South Dakota totaling only around 1,000 individuals total. All
of these individuals were raised in a captive breeding program and bred from an original
18 individuals(Belitsky et al. 1994),these were the last remaining black-footed ferrets
known in the wild before the captive breeding program (U.S. Fish and Wildlife
Service 1988). Due to this problem the genetic diversity of the Black-footed ferrets
is rather low and they are very susceptible to being wiped out entirely. After they
get through this bottleneck, however, they will be stronger than ever, that is IF they get
through this bottleneck.
Evolution
It is speculated that
Black-footed ferrets evolved in Europe from weasel like ancestors sometime in the middle
Pleistocene epoch (approximately 3-4 million years ago) (Anderson et al 1986). The
earliest known species of ferrets is M. stromeri, this species is thought to have given
rise to M. putoris (the European polecat), M. eversmanni (the Siberian polecat), and M.
nigripes (the black-footed ferret). The European polecat is believed to be the
ancestor of the domestic ferret.
During the late Pleistocene
(maybe 100,000 years ago) black-footed ferrets are thought to have migrated to north
America from Siberia across the bearing land bridge while all of the water that is now the
ocean was suspended as ice. These ferrets are then thought to have reached the great
plains through the ice free passageways.
Molecular data seems to indicate that the
black-footed ferret split from its Siberian ancestors somewhere between .5 and 2 million
years ago.
Interesting Facts
Since these animals are
nocturnal and very elusive, it is virtually impossible to get a good count of them, which
is why no one has ever gotten a good count of them historically. They were first
scientifically recognized in 1851 in a book by John James Audobon but were not spotted
again for 20 years (Anderson et al, 1986). Between this time and the late
1950’s ferrets were thought to occur at pretty low densities throughout the great
plains. In the 60’s, however there was only one known population which was
studied intensively until its disappearance in 1974. At this time the species was
thought to be extinct. (Biggins et al 1989).
In 1981 a small population of
black-footed ferrets was discovered in northwestern Wyoming consisting of around 130
animals. This population was also studied intensively. The population dropped
to 18 individuals shortly after their rediscovery due to sylvatic plague and canine
distemper (Anderson et al 1986). These remaining 18 individuals were placed in
captivity in order to try for a captive breeding program which succeeded. This
program is still underway and is thriving with over 400 animals in seven separate
locations (Belitsky, Van Pelt, and Hanna 1994)
Since they have been listed as
endangered species, the black-footed ferrets have been placed on a recovery plan with
three basic goals the first of which has already been achieved: a) increasing the
captive population of ferrets to 200 breeding adults by 1991; b) establishing a
pre-breeding census population of 1,500 free ranging breeding adults in ten or more
different populations, with no fewer than 30 breeding adults in each population by 2010;
and c) encouraging the widest possible distribution of reintroduced animals throughout
their historic range (U.S. Fish and Wildlife Services 1988).
From what I have found out
through researching this paper it does not seem that these goals are too unrealistic and
this plan may actually work. The dangerous thing that I see here is that all of
these animals will have come from an original 18 individuals and that is a pretty serious
genetic bottleneck to get through. If they can get through this though they will be
able to get through anything. It appears that the next few years will be very
trying times for these critters but the fact that so much is being done to help them get
their feet on the ground may make their success a certainty.
Links: http://www.r6.fws.gov/pressrel/96-48.html
Bibliography
Anderson, E., S.C. Forrest, T.W. Clark, and L.
Richardson. 1986. Paleobiology, biogeography, and systematics of the black-footed ferret
(Mustela nigripes) (Audubon and Bachman), 1851. Great Basin Naturalist Memoirs
8:11-62.
Anderson, S. 1972. Mammals of Chihuahua--taxonomy and distribution. Bulletin of the American Museum of Natural History 148(2):280-281.
Belitsky, D.W., W.E. Van Pelt, and J.D. Hanna. 1994. A cooperative reintroduction plan for black-footed ferrets. Aubrey Valley, Arizona. Arizona Game and Fish Department, Phoenix, Arizona. 33 pp.
Biggins, D., B. Miller, L. Hanebury, B. Oakleaf, A. Farmer, R. Crete, and A. Dood. 1989. A system for evaluating black-footed ferret habitat. Unpubl. Rept. for the Black-footed Ferret Interstate Coordinating Committee. USFWS, Fort Collins, Colorado. 25 pp.
Forrest, S.C., T.W. Clark, L. Richardson, and T.M. Campbell III. 1985. Black-footed ferret habitat: some management and reintroduction considerations. Wyoming Bureau of Land Management, Wildlife Technical Bulletin, No. 2. 49 pp.
Henderson, F.R., P.F. Springer, and R. Adrian. 1969. The black-footed ferret in South Dakota. South Dakota Department of Game, Fish and Parks, Tech. Bull. 4:1-36.
U.S. Fish and Wildlife Service. 1988. Black-footed ferret recovery plan. U.S. Fish and Wildlife Service, Denver, Colorado. 154 pp.
Map courtesy of:
http://www.ngpc.state.ne.us/wildlife/ferret.html
send comments to bholzman@sfsu.edu
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