Historical habitats of the black-footed ferret included shortgrass prairie [41,49,65], mixed-grass prairie [27,49], desert grassland [51], shrub steppe [12,75], sagebrush steppe [7,11,12,20,30], mountain grassland, and semi-arid grassland [37].
Vegetation types occurring in 4 inventoried historic black-footed ferret habitats in Wyoming include: birdfoot sagebrush (Artemisia petadifida)/ western wheatgrass (Pascopyron smithii); big sagebrush (Artemisia tridentata); low sagebrush (Artemisia arbuscula)/mixed-grass (bottlebrush squirreltail (Elymus elymoides), western wheatgrass, and Sandberg bluegrass (Poa secunda)); Gardner's saltbush (Atriplex gardneri)/mixed-grass (Sandberg bluegrass and cheatgrass (Bromus tectorum)); thickspike wheatgrass (Elymus lanceolatus)-threadleaf sedge (Carex filifolia); mixed shrub (Artemisia spp.)/mixed-grass (thickspike wheatgrass and blue grama (Bouteloua gracilis)); and Gardner's saltbush [20].
Current habitat occupied by black-footed ferrets near Meeteetse, Wyoming, is wheatgrass (Agropyron spp.)-needlegrass (Stipa spp.) shrubsteppe (Artemisia spp.), dominated by bluebunch wheatgrass (Pseudoroegneria spicata), western wheatgrass, prairie junegrass (Koeleria macrantha), and big sagebrush [12,16,17,20,30]. Suitable habitat for black-footed ferrets near Meeteetse, Wyoming, may include meadows or saltbush (Atriplex spp.)/rabbitbrush (Chrysothamnus spp.) [5].
Information about plant communities at black-footed ferret reintroduction sites is sparse. In Aubrey Valley, Arizona, habitat is grassland dominated by blue grama, galleta grass (Hilaria jamesii), Indian ricegrass (Oryzopsis hymenoides), and other unspecified grasses [1].
Black-footed ferrets use prairie dog burrows for raising young, avoiding predators, and thermal cover [28,36,39]. Six black-footed ferret nests found near Mellette County, South Dakota, were lined with buffalo grass (Buchloe dactyloides), prairie threeawn (Aristita oligantha), sixweeks grass (Vulpia octoflora), and cheatgrass [65]. High densities of prairie dog burrows provide the greatest amount of cover for black-footed ferrets [28,39,61]. Black-tailed prairie dog colonies contain a greater burrow density per acre than white-tailed prairie dog colonies, and may be more suitable for the recovery of black-footed ferrets [39].
Type of prairie dog burrow may be important for occupancy by black-footed ferrets. Black-footed ferret litters near Meeteetse, Wyoming, were associated with mounded white-tailed prairie dog burrows, which are are less common than non-mounded burrows. Mounded burrows contain multiple entrances and probably have a deep and extensive burrow system that protects kits [28,39]. According to Richardson and others [61], however, black-footed ferrets used non-mounded prairie dog burrows (64%) more often than mounded burrows (30%) near Meeteetse, Wyoming.
The historical range of the black-footed ferret was closely correlated with, but not restricted to, the range of prairie dogs (Cynomys spp.). Its range extended from southern Alberta and southern Saskatchewan south to Texas, New Mexico, and Arizona [18,37,70].
As of 2007, the only known wild black-footed ferret population is located on approximately 6,000 acres (2,428 ha)in the western Big Horn Basin near Meeteetse, Wyoming [13,15,17,18,30,39,45,61]. It is possible that other wild black-footed ferret populations exist but remain undetected [12,37]. Since 1990, black-footed ferrets have been reintroduced to the following sites: Shirley Basin, Wyoming; UL Bend National Wildlife Refuge and Fort Belknap Reservation, Montana; Conata Basin/Badlands, Buffalo Gap National Grasslands, and the Cheyenne River Sioux Reservation in South Dakota; Aubrey Valley, Arizona [4,71]; Wolf Creek, Colorado; Coyote Basin, straddling Colorado and Utah [4]; and northern Chihuahua, Mexico [71]. Additional sites are being considered for the reintroduction of black-footed ferrets. NatureServe provides a distributional map for black-footed ferrets.
Up to 91% of black-footed ferret diet is composed of prairie dogs [18,34,36,65,66]. Most research indicates that prairie dogs are required prey for black-footed ferrets [6,10,13,16,26,36,53,53,64,67]. However, according to Owen and others [58], established colonies of prairie dogs may not be a prerequisite for successful reintroductions of black-footed ferrets. Anecdotal observations and 42% of examined fossil records indicated that any substantial colony of medium- to large-sized colonial ground squirrels, such as Richardson's ground squirrels (Spermophilus richardsonii), may provide a sufficient prey base and a source of burrows for black-footed ferrets. This suggests that black-footed ferrets and prairie dogs did not historically have an obligate predator-prey relationship [58].
Diet of black-footed ferrets varies depending on geographic location. In western Colorado, Utah, Wyoming, and Montana, black-footed ferrets historically associated with white-tailed prairie dogs and were required to find alternate prey when white-tailed prairie dogs hibernated for 4 months of the year [10,34]. In Wyoming, alternate prey items consumed during white-tailed prairie dog hibernation included voles (Microtus spp.) and mice (Peromyscus spp. and Mus spp.) found near streams. In South Dakota, black-footed ferrets associate with black-tailed prairie dogs. Because black-tailed prairie dogs do not hibernate, little seasonal change in black-footed ferret diet is necessary [10,61].
In Mellette County, South Dakota, black-tailed prairie dog remains occurred in 91% of 82 black-footed ferret scats. Mouse remains occurred in 26% of scats. Mouse remains could not be identified to species; however, deer mice, northern grasshopper mice (Onychomys leucogaster), and house mice (Mus musculus) were captured in snap-trap surveys [66]. Potential prey items included thirteen-lined ground squirrels (Spermophilus tridecemlineatus), plains pocket gophers (Geomys bursarius), mountain cottontails (Sylvilagus nuttallii), upland sandpipers (Bartramia longicauda), horned larks (Eremophila alpestris), and western meadowlarks (Sturnella neglecta) [36].
Based on 86 black-footed ferret scats found near Meeteetse, Wyoming, 87% of black-footed ferret diet was composed of white-tailed prairie dogs. Other food items included deer mice (Peromyscus maniculatus), sagebrush voles (Lemmiscus curtatus), meadow voles (Microtus pennsylvanicus), mountain cottontails , and white-tailed jackrabbits (Lepus townsendii) [7]. Water is obtained through consumption of prey [39].
One adult female black-footed ferret and her litter require approximately 474 to 1,421 black-tailed prairie dogs/year or 412 to 1,236 white-tailed prairie dogs/year for sustenance. These figures assume that each adult black-footed ferret occupies 1 prairie dog colony, each young black-footed ferret will disperse to a new colony when mature, and prairie dogs are the only prey species available. This dietary requirement would require protection of 91 to 235 acres (37-95 ha) of black-tailed prairie dog habitat or 413 to 877 acres (167-355 ha) of white-tailed prairie dog habitat for each female black-footed ferret with a litter [68].
As of 2007, no research has examined HABITAT RELATED FIRE EFFECTS for the black-footed ferret, and little is known about the effects of fire on prairie dogs. Despite the lack of information, some inferences may be possible. Because black-footed ferrets and prairie dogs occupy the same vegetation communities, HABITAT RELATED FIRE EFFECTS may be similar between the 2 species. If fire decreases or destroys prairie dog populations, associated black-footed ferret populations would most likely suffer from a loss in the prey base (see Food habits) and cover (see Cover Requirements).
An FEIS review on the black-tailed prairie dog suggests that fire may have positive or negative effects, depending on burn severity and season. Low-severity burns conducted during spring in non-drought years may stimulate the growth of black-tailed prairie dog colonies by reducing vegetational height and density at the colony periphery [24,25,35,40,42,43,44,55,57,60,69,73,76]. Prescribed burning and mechanical brush removal around the perimeter of black-tailed prairie dog colonies may encourage the expansion of black-tailed prairie dog colonies. High-severity burns have the potential of reducing habitat quality in a black-tailed prairie dog colony, at least in the short-term [67]. During the plant growing season, the absence of fire provides optimal conditions for black-tailed prairie dog colony growth [44]. For more information about HABITAT RELATED FIRE EFFECTS for the black-tailed prairie dog, see the FEIS review on the black-tailed prairie dog.
To increase the total area of prairie dog colonies in locations such as Grasslands National Park, range improvement via burning, seeding, grazing, or mowing tall vegetation is recommended before introducing black-footed ferrets [45]. Reintroductions of black-footed ferrets have been carried out at several locations (see Animal Distribution and Occurrence) but as of 2007, very little information has been published about habitat types at reintroduction sites, so HABITAT RELATED FIRE EFFECTS are unknown. If the habitat type is known at a black-footed ferret reintroduction site, refer to the table below for fire regime information.
The following table provides fire regime information on vegetation communities in which black-footed ferrets may occur. The selection of vegetation communities was based on vegetation communities inhabited by black-footed ferrets and prairie dogs, as well as limited historical data on black-footed ferret habitat. Black-footed ferrets may not currently occur in all of the habitat types listed, and some community types, especially those used rarely, may be omitted.
As of December 2006, 700 black-footed ferrets exist in the wild [71]. The national goal for a change in status of the black-footed ferret from endangered to threatened is to establish 10 wild, self-sustaining populations, each containing >30 breeding adults, and a total of 1,500 individuals spread over the widest possible geographic area [16,71]. Recovery efforts for black-footed ferrets include preserving prairie dog habitat [7,10,11,12,13,16,53,67], preserving remaining wild black-footed ferret populations, locating new black-footed ferret populations, and captive breeding and reintroduction into wild habitats [11,13,39,49].
Historically, large, nearly contiguous prairie dog colonies were interspersed with small, isolated colonies [28]. As a result of habitat fragmentation and eradication programs, prairie dog colonies are now smaller and more fragmented [7]. Prairie dog populations have recovered in many areas of the United States; however, the size and distribution of protected colonies are probably not sufficient to support large, stable populations of black-footed ferrets [53]. Clark [11] suggests that in rare species management, habitat should receive priority over scientific measurements.
To attract and maintain black-footed ferret populations, colony size and intercolony distance of prairie dogs are important [16,28]. Small peripheral prairie dog colonies that are associated with larger prairie dog colonies may be beneficial for occupancy by black-footed ferrets [30]. Hillman and others [38] and Forrest and others [28] recommend that each prairie dog colony within a complex of prairie dog colonies be >30 acres (12 ha), and ideally >124 acres (50 ha) in area. A preliminary estimate of 9,884 to 14,830 acres (4,000-6,000 ha) of prairie dog habitat is needed to support a minimum viable population of 100 black-footed ferrets [28,39]. Prairie dog complexes of this size are ideal but rare. Black-footed ferret populations can be maintained on smaller prairie dog complexes if genetic and population manipulations are conducted [28]. If prairie dog colonies are too small and spaced too far apart, black-footed ferrets will not be able to sustain themselves due to lack of food, burrows, and thermal cover. If prairie dog colonies are large and close together, it is easier for black-footed ferrets to move among prairie dog colonies [28,39]. In order to support black-footed ferret populations, most prairie dog colonies within a complex should occur within 4 miles (7 km) of each other, which is the distance that 1 black-footed ferret may travel in 1 night [28]. See Forrest and others [28] for a hypothetical prairie dog complex that may support black-footed ferrets.
White-tailed prairie dogs and black-tailed prairie dog colonies may offer slightly different advantages to black-footed ferrets. Some research suggests that black-footed ferrets may have a better chance of survival within black-tailed prairie dog colonies located in the Great Plains than those within white-tailed prairie dog colonies located in Montana, Wyoming, Utah, and Colorado [10,16]. Great Plains habitat supports dense colonies of black-tailed prairie dogs covering extensive areas, compared to white-tailed prairie dog habitat, where populations rarely exceed 100 individuals or several hectares in size. Burrow density is greater in Great Plains habitat, providing more cover for black-footed ferrets [39]. Because black-tailed prairie dogs do not hibernate, they provide a year-round food source for black-footed ferrets. The Great Plains also have more rainfall and more productive vegetation than white-tailed prairie dog habitat [10,16,39]. Other research suggests that black-footed ferrets have a better chance of survival within white-tailed prairie dog colonies because white-tailed prairie dogs occupy less-defined living areas, so the spread of sylvatic plague is inhibited [4,28].
A habitat suitability index model was designed by Houston and others [39] to locate reintroduction sites for black-footed ferrets. The model assumes that black-footed ferrets can meet year-round requirements in prairie dog colonies provided that prairie dog colonies are large enough, their burrows are numerous enough, and adequate prey are available for black-footed ferrets. The habitat suitability model should apply throughout the black-footed ferret's historic range [39]. A field habitat model was created by Miller and others [54] to compare prairie dog complexes with known black-footed ferret habitat. The model was created as an inexpensive method to search for black-footed ferret populations and to provide a rapid method for initial identification of prairie dog complexes to be considered for reintroduction sites. After sites are identified, they could be analyzed for reintroduction potential by Houston and others' [39] model [54].
Locating additional wild black-footed ferret populations may increase chances of recovery [16]. Trench-like formations are reliable indicators of black-footed ferret presence. Black-footed ferrets dig 2 to 10 foot (1-3 m) long trenches in prairie dog burrows to modify burrows and locate prey [36,49,61]. Prairie dogs destroy the trenches and plug new black-footed ferret burrows within 2 hours of sunrise. Black-footed ferret surveys must therefore be conducted before sunrise [49].
Captive breeding currently occurs at several zoos and the National Black-footed Ferret Conservation Center in Wyoming [71]. Captive breeding of black-footed ferrets allows population genetics, predation, and disease to be monitored and controlled [53]. Breeding black-footed ferrets in captivity and finding suitable sites for reintroduction are difficult [50]. Some problems associated with raising black-footed ferrets in captivity include abnormal physical features, lack of critical behavioral skills, and diseases [31]. For information about husbandry and veterinary care of black-footed ferrets, see Carpenter and Hillman [8]. Despite positive results with captive breeding, habitat destruction and disease in natural habitats will continue to be an issue [53].
Habitat management activities suggested for black-footed ferrets occupying white-tailed prairie dog colonies include: 1) recording white-tailed prairie dog emergence and breeding in late winter; 2) determining white-tailed prairie dog reproductive success in late spring; 3) mapping active and inactive white-tailed prairie dog colonies each fall; and 4) surveying alternate prey populations in late summer and early fall. For a detailed outline of annual monitoring and protection management needed for black-footed ferrets in Meeteetse, Wyoming, see Clark [13].
For information about current recovery efforts for the black-footed ferret, see the website for the National Black-Footed Ferret Recovery Program.
Domestic livestock grazing: According to Carrier and Czech [9], where wildlife occupy ecosystems used for livestock forage, grazing often alters these ecosystems, and native species often experience population declines as a result. Black-footed ferrets are a "priority species" in Arizona and New Mexico, meaning that they should receive greater consideration than non-priority wildlife species during development of management strategies related to livestock grazing [78].
Linder and others [48] recommend preserving prairie dog colonies for black-footed ferrets by obtaining easements from ranchers. A rancher could continue grazing livestock in a normal manner, but an easement could stipulate that prairie dogs not be eliminated or controlled using methods that are detrimental to black-footed ferrets. The rancher could be compensated for any increase in the size of prairie dog colonies. Miller and others [53] suggest an integrated management plan that satisfies ranchers and the conservation of grasslands. Federal money that is traditionally allocated to the prairie dog poisoning program could be used as a rebate for ranchers that manage livestock and preserve prairie dog colonies [53].
Other: Oil and natural gas exploration and extraction can have detrimental impacts on prairie dogs and black-footed ferrets. Seismic activity collapses prairie dog burrows. Other problems include potential leakages and spills, increased roads and fences, increased vehicle traffic and human presence, and an increased number of raptor perching sites on power poles. Traps set for coyotes, American mink (Mustela vison), and other animals may harm black-footed ferrets [13].
Native American tribes including the Crow, Blackfoot, Sioux, Cheyenne, and Pawnee used black-footed ferrets for religious rites and for food [10].
The black-footed ferret is apparently an obligate-dependent species (but see [58]), requiring white-tailed prairie dogs, black-tailed prairie dogs, or Gunnison's prairie dogs (Cynomys gunnisoni) for survival (see Food habits and Cover Requirements) [6,10,13,29,36,49,53,53,54,64].
The distribution, density, and potential for prairie dog colony expansion are important factors in identifying preferred habitat for black-footed ferrets [20,28]. Vegetation does not appear to have a direct influence on black-footed ferret distribution [20,28] and should not be considered an important factor when identifying suitable habitat for reintroduction [20].
Stand- and landscape-level habitat: As of 2007, the only wild population of black-footed ferrets occurs within 37 white-tailed prairie dog colonies in a grass/shrubsteppe vegetation community near Meeteetse, Wyoming (see Animal Distribution and Occurrence) [12,16,17,20,30]. Vegetation has been heavily grazed by domestic sheep, cattle, and horses for over 100 years [20]. Elevation ranges from 6,496 to 7,513 feet (1,980-2,290 m), and slopes do not exceed 30% [20,28]. Soils are shallow (1.6 feet (0.5 m)) [28], well-drained, and comprised of clay loams or clays derived from shale parent materials, which are ideal for prairie dog burrow construction. For more details on vegetation type and total percentage of cover, shrub density, topography, soils, climate, and geology near Meeteetse, Wyoming, see Collins and Lichvar [20] and Clark [13].
Black-footed ferrets cannot sustain their populations if prairie dog colonies are too small and the intercolony distance is too large [39]. In general, 1 black-footed ferret requires an area of 100 to 120 acres (40-49 ha) containing prairie dogs to survive [15,18,39]. To support 1 litter, approximately 99 to 148 acres (40-60 ha) of prairie dog habitat are required [18,28,30,38]; however, these numbers may vary depending on whether black-footed ferrets occupy white-tailed prairie dog colonies or black-tailed prairie dog colonies (see Food habits) [68].
In Mellette County, South Dakota, black-footed ferrets occupied black-tailed prairie dog colonies. Before the population disappeared, black-footed ferrets occupied 14 of 86 black-tailed prairie dog colonies, ranging from 20 to 35 acres (8-14 ha) in size. Four sites were located near creeks, 5 were in rolling grasslands, 4 were on flatlands, and 1 was located in a badland area [36].
Near Meeteetse, Wyoming, black-footed ferrets live within white-tailed prairie dog colonies, which range from 1.2 to 3,217.0 acres (0.5-1,302.0 ha) [28]. The mean distance between white-tailed prairie dog colonies is 0.57 miles (0.92 km) (range 0.08 to 2.30 miles (0.13-3.70 km)) [28,39,61]. The mean distance between white-tailed prairie dog colonies inhabited by black-footed ferrets is 3.4 miles (5.4 km) (range 0.6 to 6.9 miles (1.0-11.1 km)) [38].
Home range and density: Data are sparse on home range size for black-footed ferrets. Female black-footed ferrets have smaller home ranges than males. Home ranges of males may sometimes include the home ranges of several females [5,28,61]. Adult females usually occupy the same territory every year [53]. A female that was tracked for 4 months (December to March) occupied 39.5 acres (16.0 ha). Her territory was overlapped by a resident male that occupied 337.5 acres (136.6 ha) during the same period [28].
The average density of black-footed ferrets near Meeteetse, Wyoming, is estimated at 1 black-footed ferret /99 to148 acres (40-60 ha). As of 1985, 40 to 60 black-footed ferrets occupied a total of 6,178 to 7,413 acres (2,500-3,000 ha) of white-tailed prairie dog habitat [28,29,39].
Movement: From 1982 to 1984, the average year-round movement of 15 black-footed ferrets between white-tailed prairie dog colonies was 1.6 miles/night (2.5 km) ((SD 1.1 miles (1.7 km)) [28]. Movement of black-footed ferrets between prairie dog colonies is influenced by factors including breeding activity, season, sex, intraspecific territoriality, prey density, and expansion of home ranges with declining population density [5,12,28,30,61]. Movements of black-footed ferrets have been shown to increase during the breeding season [12,28]; however, snow-tracking from December to March over a 4-year period near Meeteetse, Wyoming revealed that factors other than breeding were responsible for movement distances [61]. One black-footed ferret (sex not given) near Meeteetse, Wyoming, traveled an average of 331 feet (101 m)/night prior to the breeding season and 19,370 feet (5,905 m)/night during the breeding season [12].
Temperature is positively correlated with distance of black-footed ferret movement [61]. Snow-tracking from December to March over a 4-year period near Meeteetse, Wyoming, revealed that movement distances were shortest during winter and longest between February and April, when black-footed ferrets were breeding and white-tailed prairie dogs emerged from hibernation. Nightly movement distance of 170 black-footed ferrets averaged 0.87 miles (1.41 km) (range 0.001 to 6.91 miles (0.002-11.12 km)). Nightly activity areas of black-footed ferrets ranged from 1.0 to 337.5 acres (0.4-136.6 ha), and were larger from February to March (x=110.2 acres (44.6 ha)) than from December to January (x=33.6 acres (13.6 ha)) [61]. Adult females establish activity areas based on access to food for rearing young. Males establish activity areas to maximize access to females, resulting in larger activity areas than those of females [61].
Prey density may account for movement distances. Black-footed ferrets may travel up to 11 miles (17 km) to seek prey, suggesting that they will interchange freely among white-tailed prairie dog colonies that are less than 11 miles apart [28]. In areas of high prey density, black-footed ferret movements were nonlinear in character, probably to avoid predators [61]. From December to March over a 4-year study period, black-footed ferrets investigated 68 white-tailed prairie dog holes per 1 mile (2 km) of travel/night. Distance traveled between white-tailed prairie dog burrows from December to March averaged 74.2 feet (22.6 m) (n=149 track routes)[61].
Population trends: Black-footed ferrets experience large population fluctuations that are determined by population density, prey availability, predation, and disease [30]. Populations are highest after kits first appear aboveground in summer [29,30]. A conservative minimum viable population size estimate for black-footed ferrets based on genetic considerations is 100 breeding individuals/12,360 acres (5,000 ha) [12,28,39] (see Management Considerations).
LIFE HISTORY:
Little is known about the life history, behavior, or ecology of black-footed ferrets due to their nocturnal and subterranean habits [29,37,49,53,61] and their rarity. Reproductive physiology of the black-footed ferret is similar to that of the European polecat (Mustela putorius) and the steppe polecat (Mustela eversmanii) [53].
Mating: Black-footed ferrets are probably polygynous, based on data collected from home range sizes, skewed sex ratios, and sexual dimorphism [5,28,30,61]. Mating occurs in February and March [15,61]. Unlike other mustelids, black-footed ferrets are habitat specialists and have low reproductive rates [8,30]. The sex ratio of adults near Meeteetse, Wyoming, was 1 male:2.2 females (n=128) [30].
Reproductive success: Reproductive success in the wild is unknown.
Gestation period and litter size: In captivity, gestation of black-footed ferrets lasts 42 to 45 days [8]. Litter size ranges from 1 to 5 kits [10,29,48]. In Mellette County, South Dakota, mean litter size was 3.4 kits (n=11) [48]. Near Meeteetse, Wyoming, mean litter size over a 4-year period was 3.3 kits (n=68) [30]. Kits are born in May and June [71] in prairie dog burrows (see Cover Requirements) [39].
Development: Kits are altricial and are raised by their mother for several months after birth [41,63]. Kits first emerge above ground in July, at 6 weeks old [30,36,71]. They are then separated into individual prairie dog burrows around their mother's burrow [36,53,63]. Kits reach adult weight and become independent several months following birth, from late August to October [5,30,36,63]. Sexual maturity occurs at 1 year old [36].
Social organization: Black-footed ferrets are solitary, except when breeding or raising litters [28,39,53,61,62].
Habits: Black-footed ferrets are primarily nocturnal [10,31,39,41]. They are most active above ground from dusk to midnight and 4 AM to midmorning [36]. Aboveground activity is greatest during late summer and early fall when juveniles become independent [5,36]. Climate generally does not limit black-footed ferret activity [36,61], but they may remain inactive inside burrows for up to 6 days at a time during winter [15].
Dispersal: Intercolony dispersal of juvenile black-footed ferrets occurs several months after birth, from early September to early November. Dispersal distances may be short or long. Near Meeteetse, Wyoming, 9 juvenile males and 3 juvenile females dispersed 1 to 4 miles (1-7 km) following litter breakup. Four juvenile females dispersed a short distance (<0.2 miles (0.3 km)) but remained on their natal area. One juvenile female remained on her mother's home range and reared a litter the following year in her mother's absence [30].
Mortality: Primary causes of mortality include habitat loss, human-introduced diseases, and indirect poisoning from prairie dog control [10,14,15,36,41,50,63,71]. Annual mortality of juvenile and adult black-footed ferrets over a 4-year period ranged from 59% to 83% (n=128) near Meeteetse, Wyoming [30]. During fall and winter, 50% to 70% of juveniles and older animals "disappear" due to emigration or death [28,29,30]. Average lifespan in the wild is probably only 1 year [29] but may be up to 5 years [4,41]. Males have higher rates of mortality than females due to longer dispersal distances when they are most vulnerable to predators [30].
Given an obligate-dependence of black-footed ferrets on prairie dogs (but see [58]), black-footed ferrets are extremely vulnerable to prairie dog habitat loss (see Preferred Habitat and Management Considerations) [53,54]. Habitat loss results from agriculture, livestock use, and other development [56,71].
Black-footed ferrets are susceptible to numerous diseases. They are fatally susceptible to canine distemper (Morbilivirus) [8,30,37], introduced by striped skunks (Mephitis mephitis), common raccoons (Procyon lotor), red foxes (Vulpes vulpes), coyotes (Canis latrans) [15,16], and American badgers (Taxidea taxus) [15]. A short-term vaccine for canine distemper is available for captive black-footed ferrets, but no protection is available for young born in the wild [8,31]. Other diseases that black-footed ferrets are susceptible to include rabies, tularemia, and human influenza [41]. Sylvatic plague (Yersinia pestis) probably does not directly affect black-footed ferrets, but epidemics in prairie dog towns may completely destroy the black-footed ferrets' prey base (see Food habits) [19,30,41,50,63].
