Black-Footed Ferret: From Captivity to Release
Omaha’s Henry Doorly Zoo, Omaha, NE
Attempts to breed the ferrets got off to a slow start. No kits were born in 1986, during the ferrets’ first breeding season in captivity. Eight black-footed ferrets were born to two females in 1987 at Sybille. Seven survived, and were followed by 34 surviving kits in 1988, 58 in 1989, and 66 in 1990.
In 1988, the U. S. Fish & Wildlife Service developed the “Black-footed Ferret Recovery Plan” which emphasized species preservation through natural breeding, development of assisted reproductive technology, and establishment of multiple reintroduction sites. The objective of the captive breeding program was to maintain 240 ferrets (90 males, 150 females) of prime breeding age (1-3 years old) n captivity, to be subdivided to different locations in order to avoid extinction through catastrophe at a single facility. The strategy or the reproductive technology program was to support captive breeding efforts by developing artificial insemination using fresh or cryopreserved sperm. One high priority for protecting genetic diversity was to establish a “Black-footed Ferret Genome Resource Bank,” a frozen repository of sperm from the most genetically valuable males.
Since 1991, the cooperative effort among the seven breeding facilities has been guided by the American Zoo and Aquarium association’s (AZA) Black-footed Ferret Species Survival Plan (SSP).
Tie seven black-footed ferret captive breeding centers take extreme cautions to minimize stress and disease risk to the ferrets. Since ferrets are highly susceptible to canine distemper and human respiratory illnesses such as colds and flu, visitors are generally not allowed in areas where ferrets are housed. Ferret keepers typically shower before entering the facility, and wear freshly laundered clothes, clean shoes, and a surgical mask when working with the ferrets.
Since black-footed ferrets are solitary animals, they are housed individually in large, indoor enclosures. Ferrets are generally cleaned and fed once a day, and other activity in rooms housing ferrets is kept to a minimum to avoid undue stress on the animals.
Techniques, such as semen cryopreservation and artificial insemination, allow animals to breed that would not breed naturally, perhaps due to behavior problems such as aggression towards mates. These techniques can also be used to breed animals at different locations. Rather than moving animals, sperm that has been cryopreserved, or frozen, can be shipped for use in artificial insemination.
Successful artificial insemination for black-footed ferrets was developed by NOAHS reproductive biologist Dr. JoGayle Howard. She had her first success with this technique in Wyoming in 1981. A female ferret is inseminated using a method called laparoscopic intrauterine artificial insemination. This surgical technique uses a slender instrument with lenses, called a laparoscope, to deposit; men directly into the uterus of the female. During these procedures, the ferrets are given the same level of care provided to people in a human hospital.
Ferrets in excess of the SSP needs are available for reintroduction into suitable habitats in the wild. All black-footed ferrets selected for release are given a complete physical examination, vaccinated for canine distemper, given an ear tattoo, and a microchip transponder is implanted under the skin to further aid in identification.
Black-footed ferrets born and reared in indoor cages under artificial conditions are at an obvious disadvantage for survival in the wild. For the last several years, all ferrets selected for release have been either born in, or introduced to outdoor preconditioning pens where they are exposed to natural burrow systems and prairie dog prey. These preconditioned animals have significantly higher post-introduction survival than do kits that are strictly born and reared in cages. Research has shown up to a 10-fold increase in survival. The ferret recovery program is rapidly progressing toward establishment of field breeding facilities to further expand the number and quality of ferrets available for reintroduction. In addition to an existing pen breeding program in Arizona, The U. S. Fish & Wildlife service has approved construction of a field breeding facility by the Turner Endangered Species Fund in New Mexico, and development of a similar, facility on Service refuge lands in Montana.
1998 was the most successful year to date in the history of the black-footed ferret recovery program. Reproduction far surpassed all previous years with 339 ferret kits surviving from a total of 452 born in the seven captive breeding centers. The six participating zoos produced a total of 177 ferret kits, while the National Black-footed Ferret Conservation Center produced a record 249 kits with 191 surviving. Twenty-six of the total were born in Arizona in on-site pens. Some of the surviving 18 kits will be released directly from their birth pens into the wild. This is the first time that ferrets were produced in on-site pens at an existing reintroduction area.
In the 11 years from 1987-1998, the captive-breeding program has produced approximately 2,600 ferrets, providing an opportunity to gain knowledge of ferret behavior and biology. But breeding ferrets is only the first part of the recovery program.
The black-footed ferret (mustela nigripes) is the most endangered mammal in North America. It is a member of a large group of mammals known as mustelids, or musk-producing animals.
The black-footed ferret is 18 to 24 inches long, including a 5 to 6 inch tail. It weighs only one-and-a-half to two-and-a-half pounds, with males slightly larger than females. The black-footed ferret is well adapted to its prairie environment. Its color and markings blend so well with the grassland soil and plants that it is hard to detect until it moves. It is a slender, wiry animal with a black facemask, black feet, and a black-tipped tail.
The rest of its short, sleek fur is a yellow-buff color, lighter on the belly and nearly white on the forehead, muzzle and throat. It has short legs with large front paws and claws developed for digging. The ferret’s large ears and eyes suggest that it has acute hearing and sight, but smell is probably its most important sense for hunting prey underground in the dark.
Black-footed ferrets are primarily nocturnal, making observation difficult. Most of their daytime activity is limited to the first few hours following sunrise. They spend most of their time underground in prairie dog burrows, typically spending only a few minutes above ground each day to hunt or find new burrows or mates. In the burrows, they sleep, cache their food, escape from predators and harsh weather, and give birth to their young. Ferrets do not hibernate, but in winter, the amount of time they are active and the distances they travel decrease substantially. They have been found to remain underground in the same burrow system for a week at a time in winter. In contrast, they have been observed traveling over 6 miles in one night during autumn. Distances traveled by males tend to be about double that of females.
Black-footed ferrets are very playful, especially as juveniles. Young at play will wrestle, arch their backs, and hop on their toes and hop backward with their mouths wide open – the “ferret dance.” Black-footed ferrets are very vocal. A loud chatter is used as an alarm call. A hiss is used to show agitation or fear, and whimpering sounds are used by females to encourage the young to follow. Male ferrets often “chortle” to females during breeding.
Black-footed ferrets lead solitary lives except during the breeding season or when females are caring for young. Breeding activity generally occurs in March and April, and after a gestation period of 41 to 43 days, a litter of kits is born. The average litter size is three to four young, but single kits, as well as litters of nine or ten have been recorded. Only the female cares for the young. The kits are born blind and helpless, weighing only 5 to 9 grams at birth, with thin, white hair covering their bodies. Their dark markings appear at about 3 weeks, and young kits begin to open their eyes about 35 days after birth. Black-footed ferret kits develop very rapidly and become increasingly active after their eyes are open.
Kits are about three-quarters grown by July when they first venture above ground. Long after they stop nursing, they depend on their mother for meals or meat. By late summer, the female leaves her kits in separate burrows during the day and gathers them together at night to hunt. Eventually, the young begin to hunt alone, and by September are usually independent and solitary. Both male and female ferrets become sexually mature at one year of age, and their peak reproductive period is about three to four years.
The black-footed ferret is a predator, and since ferrets are closely associated with prairie dogs, it is not surprising that nearly 90 percent of their diet is prairie dogs. The remainder of their diet includes mice, rats, ground squirrels, rabbits, birds, and occasionally reptiles and insects. Ferrets have a high metabolic rate and require large quantities of food in proportion to their body size. Food requirements vary with the seasons and among individual ferrets, but they generally consume one prairie dog every three or four days.
The ferret most commonly hunts at night when prairie dogs are asleep in the burrows and when animals who might prey on ferrets are less active. This gives the ferret an advantage over the prairie dogs, which may be as big or bigger than the ferret. Like other members of the weasel family, the ferret kills by attacking its prey at the neck or base of the skull. They prefer to kill underground, but if an above ground attack is made, the ferret will try to pull the prairie dog into a burrow. It is very risky for ferrets to hunt prairie dogs. Many ferrets in the wild often have large wounds and scars on their faces and necks – likely the result of battles with prairie dogs.
The black-footed ferret (mustela nigripes) is the only ferret species endemic to North America and has been classified as an endangered species by the U. S. Fish and Wildlife Services since 1967. Black-footed ferrets once occurred in grassland habitats throughout the Great Plains in 12 states and two Canadian provinces, and possibly portions of northern Mexico. Originally, the prairie dog ecosystem occupied 20 percent of the entire western rangeland, allowing ferrets to cover a large geographic range.
Today, less than 2 percent of their original geographic distribution remains. The slack-footed ferret’s current status is a sign of this encroached and depreciated ecosystem. Throughout their history, black-footed ferrets have been elusive. None of the early explorers, mountain men, or pioneers who crossed: the Great Plains by wagon train ever mentioned ferrets.
In 1981, a black-footed ferret was killed by a ranch dog in northwestern Wyoming. This event led to the dramatic discovery of a small group of about 130 ferrets near Meeteetse, Wyoming, in 1984, and offered a ray of hope for the species. Research conducted on he Meeteetse ferrets provided important new information on the life history and behavior of this secretive mammal. Tragically outbreaks of sylvatic plague and canine distemper killed nearly all of the Meeteetse population. The remaining 18 ferrets were taken into captivity between 1985 and 1987 in an effort to save the species. At that time, these last known ferrets were probably the rarest mammals on earth.
These captured animals were taken to a captive breeding facility in Sybille Canyon, Wyoming (now known as the National Black-footed Ferret Conservation Center). In 1987, a captive-breeding program was initiated by the U. S. Fish and Wildlife Service, the Wyoming Game and Fish Department, and the American Zoo and Aquarium Association. This program has since expanded to include 6 captive-breeding facilities in zoos across North America, including the National Zoo’s Conservation and Research Center, Front Royal, VA; Omaha’s Henry Doorly Zoo, Omaha, NE; Cheyenne Mountain Zoo, Colorado Springs, CO; Louisville Zoological gardens, Louisville, KY; the Phoenix Zoo, Phoenix, AZ; and the Toronto Zoo, Toronto, Ontario, Canada.
Since 1991, federal and state agencies, in cooperation with private landowners, conservation groups. Native Americans, and the North American zoo community, have been actively reintroducing ferrets back into the wild. Beginning in Wyoming, reintroduction efforts have since expanded to sites in Montana, South Dakota, and Arizona.
Proposed reintroduction sites have been identified in Colorado and Utah.
The Recovery Plan for the black-footed ferret calls for the establishment of 10 or more separate, self-sustaining wild populations. By the year 2010, biologists hope to have 1,500 ferrets established in the wild, with no fewer than 30 breeding adults in each population. If these objectives are met, the ferret could be down listed from endangered to threatened status.
(threats to the ferret)
Black-footed ferrets face threats in the wild from predators and disease. Coyotes, great-homed owls, golden eagles, prairie falcons, badgers, bobcats and foxes all prey on ferrets. Several diseases affect black-footed ferrets, the most serious being canine distemper and sylvatic plague. Canine distemper is thought to always be fatal to ferrets and is spread by other animals that frequent prairie dog towns, such as coyotes and badgers. Sylvatic plague, spread by fleas, is akin to the bubonic plague that devastated humans in Europe in the Middle Ages. Both ferrets and prairie dogs are susceptible to the plague, and entire dog towns can be eliminated quickly, then require 4 to 5 years to regenerate. Ferrets are also susceptible to other diseases, including rabies, tularemia and human influenza, but these are not considered serious threats.
Loss of habitat is the primary reason black-footed ferrets remain near the brink of extinction. Conversion of grasslands to agricultural uses, gas and oil drilling in the West, and widespread prairie dog eradication programs have reduced ferret habitat to less than 2 percent of what once existed. Remaining habitat is now fragmented, with prairie dog towns separated by great expanses of cropland and human development. Many other sensitive species such as burrowing owls, mountain plovers, golden eagles, swift fox, and ferruginous hawks also depend on this habitat for survival. Many of these species are closely following the ferret’s fate, and may soon require a rehabilitation program to ensure their survival.