 |
Black-footed ferret |
The black-footed ferret (Mustela nigripes) once occurred throughout the grasslands and basins of interior North America, from southern Canada to Texas [1]. Black-footed ferrets live in burrows made by prairie dogs, hunt prairie dogs for food and are obligate associates of the prairie dog [2]. Their historical range is nearly identical to that of three prairie dog species, the black-tailed prairie dog, Gunnison's prairie dog, and white-tailed prairie dog [2]. Prairie dogs were formerly abundant on the prairies of the continent and their colonies could possibly have supported as many as 5.6 million black-footed ferrets in the late 1800s [2]. With the development and improved distribution of rodenticides in the early 1900s and expanded agricultural tillage, however, prairie dogs were rapidly eliminated and are now absent from an estimated 90-95% of their historically occupied area [2].
Ferret decline was linked to this rapid decline and fragmentation of prairie dog populations [2]. Of the approximately 130 counties and provinces where ferrets had been found since 1880, only 10 were known to have ferrets by the 1960s [2]. In 1971, six ferrets were caught and removed from a declining population in South Dakota and a first effort at captive breeding was attempted [2]. The effort was unsuccessful and the last captive ferret died in 1979 [2]. Following this loss, the black-footed ferret was thought to be extinct throughout North America [2]. In 1981 however, a small relic population was discovered in a prairie dog colony near Meeteetse, Wyoming [2]. The ferrets that remained at this site were eventually brought into captivity to protect them from an outbreak of sylvatic plague and distemper [2]. These ferrets then became the founder population for reintroduction efforts [1]. Today, all ferrets known to exist in the wild are the result of reintroduction efforts [3]. Thus far, there have been 11 reintroduction sites including sites in Wyoming, Montana, South Dakota, Arizona, the Utah/Colorado border, and Mexico [4]. Between 1991 and 1999, a total of 1,185 ferrets were released [5]. Reproduction has occurred in the wild in six states [4]. Currently two reintroduced populations are established and no longer require releases of captive-raised ferrets, one in western South Dakota and the other in southeastern Wyoming [1]. Biologists estimate that a total of about 400 black-footed ferrets are alive in the wild in all the states where releases have occurred [6]. Somewhere around another 400 are typically held in captive-breeding facilities around the country [7]. WYOMING: Meeteetse: In 1981, after it was believed the black-footed ferret had become extinct, a population was discovered distributed among approximately 7,400 ac of white-tailed prairie dog colonies [2]. Total population estimates were 88 (28 adults) in 1983 and 129 (43 adults) in 1984 [2]. Between 1986 and 1987, however, canine distemper and sylvatic plague decimated the rediscovered population [2]. During this period, 18 ferrets were captured and later became the founder population for captive breeding efforts [2]. These efforts were successful and have provided ferrets for reintroduction at 11 sites in the western US [4]. Shirley Basin: In 1991, Shirley Basin, Wyoming became the first site for black-footed ferret reintroduction [8]. Currently, it is the only population of black-footed ferrets known to exist in the state [1]. Two hundred twenty eight black-footed ferrets were released in the area between 1991-94 [9]. In 1995, however, sylvatic plague caused a sharp decline in local white-tailed prairie dog populations [8]. Despite the disease, a small number of the ferrets survived [8]. In 1997, five ferrets were observed during spotlight surveys [10]. The number spotted during surveys rose to 15 in 2000, 19 in 2001, and at least 52 in 2003 [10]. Because not all of the area was searched and because spotlight surveys do not detect all ferrets these numbers represent only a portion of the population [10]. In 2004, surveys of about 10% of the suspected black-footed ferret range in the Shirley Basin discovered a minimum of 21 litters and a total of 88 animals [11]. Since 1991, the area's prairie dog acreage has increased in portions of the survey area and black-footed ferrets have been discovered in some of the new acreage [9]. In 2005, permission was granted to proceed with plans for Wyoming’s first black-footed ferret reintroduction since 1994 [11]. Plans include the release of 50 captive bred young-of-the-year into Shirley Basin [11]. SOUTH DAKOTA: Cheyenne River Sioux Reservation: In 2000, 42 ferrets were released on the Cheyenne River Sioux Reservation and those releases are continuing [3]. In 2005 it was reported that the reservation had 115 ferrets [12]. Conata Basin /Badlands site: Black-footed ferrets were reintroduced into the Conata Basin/Badlands area of southwestern South Dakota in 1994-1999 [3]. Thirty-six ferrets were released in 1994 [13]. In 1995, there were at least two wild-born litters [13]. Thirty-three more ferrets were released in 1995 and in 1996 there were as many seven as wild-born litters [14]. Releases at this site indicated that “preconditioning” ferrets to the site prior to release resulted in higher success [13]. As of 2000, this site had at least 200 ferrets and appeared to be the first established, self-sustaining wild population since reintroductions began [3]. In 2005 245 ferrets were reported [12] and because plague was confirmed in prairie dog colonies near the ferrets, a preventative treatment program was initiated [15]. In 2004, 93 ferrets were released onto the Rosebud Sioux Reservation in South Dakota [12]. In 2005 42 survivors were counted and 15 new kits were observed later that year [12]. UTAH/COLORADO: In 1999, 72 ferrets were released in Utah’s Coyote Basin located along the Colorado/Utah border [16]. Since then 255 ferrets have been released at this site [16]. This population appears to be making good progress, with a minimum of 34 animals detected on one core release area in 2002 and with documented wild production every year since 2000 [17]. In 2001, a reintroduction effort began on the Colorado side of the Colorado/Utah border [16] with the release of 35 ferrets at the Wolf Creek Management Area [18]. A total of 189 ferrets have been released at this site to date [16]. Based on a weeklong counting operation in late August 2005 where 5 sightings were confirmed, and 5 others were unconfirmed, ferrets here are surviving (although these numbers are low, they are representative of a larger population) [6]. Wolf Creek’s first confirmation of a wild-born kit took place in November 2005 [16]. ARIZONA: Reintroductions began at Aubrey Valley in Arizona in 1996 when 4 ferrets were released into large fenced enclosures on a reintroduction site in Coconino County [14]. Thirty-five ferrets were later released into ten on-site enclosures [14]. An additional 15 kits were added to the site in the fall of 1996 [14]. As of 2003, this reintroduction had moderate success with at least two successive generations of wild-born kits [17]. In 2004, 24 ferrets were captured and tagged and in 2005, 35 were captured and tagged. In both years, others were observed but not captured suggesting that there has been a solid increase in numbers [19]. MONTANA: The first reintroduction attempt in Montana was initiated on the Charles M. Russell National Wildlife Refuge in 1994 [5,14] with the release of 35 ferrets [4]. In 1995, 33 ferrets were released [4]. In 1996, at least 10 females (some wild-born) were known to have produced litters totaling at least 15 kits [14]. In the fall of 1996, an additional 39 ferrets were released [4] onto prairie dog colonies unoccupied by ferrets [14]. By fall of 1999, a total of 171 captive-reared kits had been released and the release of captive ferrets ceased [4]. Wild-born kit production increased each year to a peak of 44 observed kits from 15 litters during summer 2000 [20]. In 2001, however, a population crash began that continued through 2002 and the population appeared in danger of extirpation without additional releases [20]. Thirty-seven captive ferrets were released in 2003 and 21 more were released in 2005 and the number of wild-born ferrets increased from just a few individual in the spring of 2003 to over 10 in 2005 [4]. In 1997, a second Montana release site was established on the Fort Belknap Indian Community when 23 ferrets were released [5]. Since then, 110 black-footed ferret kits have been released at this site (the Snake Butte reintroduction site) [5]. This reintroduction has met with only moderate success [5]. Despite additional releases, as of 1999 only one litter had been born in the wild at the site [5]. MEXICO: Ninety-one captive-reared ferrets were reintroduced into northern Chihuahua, Mexico, in the fall of 2001 [17]. This site supports the largest contiguous colony of black-tailed prairie dogs found in North America today [17]. In 2002, an additional 69 were reintroduced on adjacent areas of the El Cuervo complex [17]. Initial follow-up survey results were promising, with at least 26 ferrets documented during 2002, of which nine were wild-born [17]. More recently, probably because of drought, numbers appear to have declined with only two animals seen in a recent survey [19]. CAPTIVE POPULATION: In 1988, the single captive population of black-footed ferrets held at the Wyoming Game and Fish Department’s Sybille Wildlife Research and Conservation Education Center was split into three separate captive subpopulations to avoid the possibility that a single catastrophic event could wipe out the entire population [21]. Currently, the captive ferret population is divided among seven captive-breeding facilities throughout the United States and Canada [22]. The captive population of juveniles and adult ferrets now fluctuates annually between 300 and 600 animals [22]. [1] Wyoming Game and Fish Department. 2004. Black footed ferret (Mustela nigripes). Available at <http://gf.state.wy.us/wildlife/CompConvStrategy/Species/Mammals/PDFS/Black-footed%20Ferrett.pdf>. |
|