Mustela nigripes

Written by: Jana Torrez

Biology 212

Tuesday/Thursday 12:30pm

In 1981 in northwest Wyoming, a ranch dog returned home with a strange creature in his jaws. John and Lucille Hogg had no idea that the unknown corpse was, in fact, the remains of a small mammal thought to be extinct. When the body was examined by a local taxidermy, they were all shocked to learn that the small, black and tan weasel was a black-footed ferret.

The black-footed ferret (Mustela nigripes) was first noted in 1851. James Audubon, a naturalist, and a priest, John Bachman, described the small prairie mammals in scientific literature (Miller 1996). It would be many years before their observations were taken seriously, since the nocturnal carnivores were rarely observed in the wild. This may have been one of the reasons for their sudden and negligent decline in population in the following century to come.

Native American tribes were one of the few to actively worship the black-footed ferret. Historical artifacts were discovered in Cheyenne, Blackfeet and Sioux tribe lands, revealing that the black-footed ferret's body was used to fashion sacred, ceremonial objects and headdresses (Silverstein 1995). The Sioux rightfully named the c reature "black faced prairie dog" (Silverstein 1995). While this name may seem strange since the ferret and prairie dog are so evolutionary dissimilar, the appearance of the ferret with their dark mask, and their natural habit of inhabiting prairie dog burrows for food and shelter made their name understandable. Pawnees tribesmen believed the black-footed ferret possessed special powers and worshiped them (Silverstein 1995). The Crows used the bodies for sacred ceremonies and for medical ritual (Silverstein 1995). While M. nigripes, may have played the quiet roll in the European conquest of the North American prairie, the natives saw them for their unique expertise and almost super natural talents for survival.

The black-footed ferret's ancestors were thought to originate from European ancestors. According to Miller 1996, the closest relative is the Siberian polecat. It is believed that the land bridge that once connected Siberia and Alaska allowed for the Siberian polecat to migrate and specialize into their own species (Silverstein 1995). When the land bridge split, the geographic isolation from the mother species forced adaptation. The black-footed ferret adapted for the great plains of Texas, Arizona, New Mexico, Montana and Wyoming (Silverstein 1995), becoming so specialized toward their main food source, prairie dogs, that no subspecies was ever developed (Miller 1996).

The black-footed ferret is tubular shaped, allowing them to enter and maneuver in a prairie dog burrow easily in search of prey and shelter. Their diet consists of ninety percent prairie dog and ten percent of rabbits, rodents, insects, small birds and small snakes (Silverstein 1995). Miller estimated that a black-footed ferret consumes anywhere from fifty to seventy grams of prairie dog meat a day. In order to specialize this much, it is assumed that the black-footed ferret relied heavily on the unchanging environment of the North American prairie (Miller 1996).

The prairie dog (genusCynomys) is a keystone species in North American grass lands (Miller 1996). Despite their importance in the ecosystem, settling farmers grew to loath the small creatures. A colony of about three hundred prairie dogs is said to eat as much grass and foliage as a single cow and her calf (Miller 1996). This led to massive competition between the farmers and the species. Unfortunately, when mass poisoning began, the farmers did not realize the problems this was going to cause in the future.

With a declining numbers in their food, survival was on a downturn for the black-footed ferret population throughout the continent. An adult ferret requires about one hundred acres of territory for hunting (Silverstein 1995). A ferret may travel as much as four miles in a single night in search for food (Silverstein 1995.) Once they find an occupied prairie dog hole, they waste little time in preying upon one that may be even twice their size.

The black-footed ferret is extremely skilled in their hunting techniques. A hungry ferret will be able to smell from the opening of the burrow if there are any sleeping prairie dogs below. If they find an occupied den, the ferret will slink in and seek out a dirt plug that the prairie dogs create at night for protection. The ferret will drag a pile of the dirt under its belly and push it out the mouth of the burrow before returning for another load. Once the plug is penetrated, the ferret will grab a large prairie dog by the throat and clamp down. After it has had its fill, the ferret will 'catch' it's prey in the canals of the burrow, saving it for another night (Miller 1996).

Declines in the prairie dog population forced black-footed ferrets to widen with territorial girth in search of food; this led to mating problems, as the ferrets were not accustomed to traveling more then a few miles to find a mate (Silverstein 1995). When a male does find a female in heat, he will cautiously approach the burrow and await her to exit. They then began a courtship dance. The male and female with arch their backs and circle each other with mouths open. The male will then bite the female on the nape of the neck before mounting. Copulation may last anywhere from thirty minutes to five hours. There is little known in regards to the relationship between time exerted and successful fertilization (Miller 1996). The male will leave immediately after to avoid being attacked by the territorial female. Gestation for the black-footed ferret will last for 45 days (Miller 1996). However, in the case of unfavorable conditions, the female black-footed ferret is able to delay implantation. When weather is harsh or food is scarce, the female can delay her gestation (Miller 1996). This can raise the survival rate of new born kits.

The female black-footed ferret will have four to six kits in a litter (Silverstein 1995); however, the average is 3.3 (Miller 1996). The kits are born blind and deaf, relying on their mother for everything. At six weeks, kits will begin rough housing in the nest chamber of the burrow. Sixty-five percent of bites are for the neck, practicing important hunting skills (Miller 1996). This will be important in a few more weeks, because the mother will begin to have the kits tag along on hunts to observe and learn from her technique (Silverstein 1995). It is estimated that a female black-footed ferret and her kits will need at least one hundred nine prairie dogs to sustain themselves for one year (Miller 1996). Other than starvation, kits are more vulnerable to disease and predators. Sixty to eighty percent of juveniles will die a year from causes other then disease (Miller 1996).

Throughout their history, black-footed ferrets have had to endure hardships as all species do. Unfortunately, with the expansion of man into the plains of North America, a number of problems were exacerbated to the point of bringing this weasel to the brink of extinction. Man turned on the black-footed ferret's main source of food, causing starvation and disease to spread exponentially.

Between 1880 and 1884, the Bureau of Indian Affairs passed a law allowing for farmers to mass poison the prairie dog population that was decimating their cattle ranches. $6.2 million funded these farmers in one of the largest poisoning campaigns recorded. In American history, the federal government was paying more than seventy-five percent of the costs for farmers to poison (Miller 1996). This led to starvation in the black-footed ferret population due to the mass decline in their main food source- prairie dogs. Starving ferrets resorted to scavenging on the corpses of poisoned prairie dogs, leading to second-hand poisoning. Warning were given about the damage of the poisoning; however, the Animal Damage Control Act of 1931 continued to allow "poisoning, trapping and shooting on and off federal land" (Miller 1996). The black-footed ferret became more and more endangered.

Diseases continued to wreck havoc on the surviving population as well. On top of rabies, diseases such as canine distemper, plague and pneumonia decimated the ferret population in the number of periodic epidemics. Canine distemper was thought to be introduced by European settlers in the 1800s (Miller 1996). An outbreak could lead to an entire population to die out in just a few weeks. Plague was brought over as well through infected rats. The spread of the disease depends on "soil, climate, species of fleas and the density of the species of rodent" (Miller 1996). Unfortunately, the plains were the perfect environment for the spread. Although this infected the prairie dogs mostly, this would lead to starvation and even spread of the disease through infected carcasses.

Although the young were more vulnerable, black-footed ferrets have to face predators just as all animals do. While moving from one burrow to the next, the ferrets must watch the sky for birds of prey such as the Great Horned Owl. Also, coyotes have been recorded catching ferrets, though research has indicated that the coyote does not typically consume the ferret. Theories lie on the 'catch prey' instinct of seeing a small, running creature. Captured Black-footed ferrets are typically found uneaten, buried in the substrate (Miller 1996). Badgers pose the most threat to Black-footed ferrets though, since badgers are able to smell out a burrow and unearth an unsuspecting ferret. In these circumstances, an alternate exit is used by a trapped ferret thanks to the engineering of the prairie dogs before him.

The black-footed ferrets were thought by many to be extinct. It was not until 1964 that a small population of ninety black-footed ferrets were found in South Dakota (Silverstein 1995). It took two years to pass the Endangered Species Preservation Act of 1966, protecting the black-footed ferret with mild funding for conservation (Miller 1996). In 1971, six black-footed ferrets were captured for a captive breeding program. A vaccine was given for distemper, but the dosage was too high and it killed all six of them (Miller 1996). Little was done for the conservation effort due to the lack of funding, and in October of 1985, the population dropped to sixteen (Aronin 2008). In November, there were only six (Aronin 2008). Spring brought more litters, but in June of 1986, only four adults survived (Aronin 2008). Research on a captured ferret's blood sample confirmed that canine distemper was devastating the last population of known black-footed ferrets (Miller 1996). The last known wild black-footed ferret was captured on February twenty-eighth of 1987 (Silverstein 1995).

A plan was needed in order to reintroduce the last black-footed ferrets successfully. It was estimated that in order to have a self sustaining population, at least five hundred breeding adults would be required (Silverstein 1995). There were a number of problems the black-footed ferrets would have to face once introduced. Early reintroduction methods led to ferrets starving to death. Twenty percent of the animals released survived for one month (Silverstein 1995). The solution raised was to raise the captive born black-footed ferrets in a cage with lots of hiding places (Miller 1996). This allowed them to learn different techniques of ambush and predation that would be useful in the wild. Another technique was to raise captive ferrets in enclosures on top of a colony of prairie dogs. This was researched to yield four times the success over isolated cages (Dobson 2000).

Another problem was predator detection. The captive born ferrets had no idea what a badger or bird was. Early releases found an unusually high rate of death from predators. In an experiment, scientists used a 'soft-mouthed' Labrador to study European ferrets, a close relative to the black-footed ferret. The ferret was chased by the dog, and if caught, learned very quickly to avoid dogs. This led the creation of Robo-badger. A remote control car was fitted with the hide of a badger, giving it the smell and appearance of a badger. The ferrets were chased around their enclosure until they ran into their burrow. This technique was used for birds as well, with a stuffed owl on a string. Research has shown that predator detection has increased dramatically in the newly released ferrets.

Two thousand-two hundred kits have been released in the wild between 1991 and 2008 (Aronin 2008). It was a huge landmark after the political downfalls shrouding the conservation project. Despite efforts to avoid inbreeding, the small captive population would leave a number of lasting problems in the reintroduced wild population. Research has shown that skulls of the captive ferret population is become between five to six percent smaller than earlier wild species (Wisely 2002). This could continue to cause a threat, even in the wild, since populations are geographically isolated from one another. It is believed that this could also 'suggest that genetic factors may diminish the long-term evolutionary potential and viability of this species' (Wisely 2008). According to Samantha Wisely from Kansas State University, the captive ferrets were found from six different populations in the wild (Wisely 2008). 'Forty-five percent of the ninety-seven samples had amixed genomes from different population clusters' (Wisely 2008). While this increased variability in the species population, the other fifty-five percent were highly inbred. In the end, the captive breeding program may have just prolonged the species' survival for a few more generations. Genetic problems may be their downfall, after so many hardships and human-induced disasters.

The black-footed ferret has been an ongoing conservation effort, facing disease, infection, starvation and poisoning in an attempt to bring them back from the brink of extinction. As few as seven individuals existed at one time, and from them, an amazing program was conducted, bringing the total re-release number up to over two thousand. While genetics may cause future problems with mutations and cancers, the numbers and the survival rate continues to flourish. With no further interference from farmers, the black-footed ferret may just be able to reestablish itself as the only native North American ferret.

Citations

Aronin, Miriam. "Black-Footed Ferrets: Back from the Brink". Bearport Publishing. New York, New York. 2008.

Dobson, Andy; Lyles, Annarie. Black-Footed Ferret Recovery. Science. 2000 May 1. Vol. 288, Issue 5468. Science. 2000.

Miller, Brian; Reading, Richard; Forrest, Steve. "Prairie Night: Black-Footed Ferrets and the Recovery of Endangered Species". Smithsonian Institution Press. Washington and London. 1996.

Silverstein, Alvin; Silverstein, Virginia; Nunn, Silverstein. "The Black-Footed Ferret". The Millbrook Press. Brookfield, Connecticut. 1995.

Wisely, S.M.; Ososky, J.J.; and Buskirk, S. W.. Morphological changes to Black-Footed Ferret (Mustela nigripes) resulting from captivity. Canada Journal of Zoology. Sept. 2002. Vol. 80, Issue 9. NRC Canada. 2002.

Wisely, Samantha; Statham, Mark; and Fleischer, Roberts. Pleistocene Refugia and Holocene Expansion of the Grassland-Dependent Species, the Black-Footed Ferret (Mustela nigripes). American Society of Mammalogists. Feb. 2008, Vol. 89 Issue 1. Allen Press Publishing Inc. 2008.