Black-footed ferret (Mustela nigripes)
Magnus McCaffery, Levi Fettig
Vermejo Park Ranch, NM
Bad River Ranches, SD
US Fish & Wildlife Service
New Mexico Department of Game & Fish
South Dakota Game, Fish & Parks
National Fish & Wildlife Foundation
The near extinction of black-footed ferrets was a direct result of the range-wide decline of their primary prey item—prairie dogs (Cynomys spp.) Prairie dog conservation remains the primary challenge in black-footed ferret recovery. The range-wide loss of prairie dogs, and by extension the black-footed ferret, is attributable to: non-native disease sylvatic plague (Yersinia pestis); loss of habitat and habitat fragmentation; and human persecution.
- First listed as endangered throughout its historic range in 1967 under the Endangered Species Preservation Act; once the ESA was passed in 1973, the species was moved to that list
- Listed as a Protected Furbearer in New Mexico
- Listed as Endangered in South Dakota
Turner Endangered Species Fund’s (TESF) longstanding goal has been to work with state and federal agencies and other partners in meeting downlisting criteria for the species.
The black-footed ferret recovery plan requires that a recovery site maintain a minimum of 30 adult ferrets over a 3-year period to meet downlisting criteria. Our objectives involve managing prairie dog colonies and essential habitat of black-footed ferrets, and restoring viable ferret populations to Vermejo, Bad River and Z Bar Ranches that meet or exceed these downlisting criteria.
Supporting Rationale for Objective
Black-footed ferrets are an obligate predator of prairie dogs, and prairie dogs historically required grazing by bison throughout a large portion of their historical range in order to persist. Thus, the black-footed ferret project is a natural fit for many Turner properties and provides the opportunity to complement commercial commodity production with native species restoration.
The foremost range wide challenge facing black-footed ferret recovery is plague. TESF will assist in efforts to mitigate or prevent the impacts of the disease by supporting and implementing innovative plague management research on Turner properties.
Extant black-footed ferret populations, both captive and wild, can all be traced to seven founders captured in Meeteetse, WY and brought into captivity from 1985-1987. Today, the black-footed ferret remains one of the rarest mammals on the planet with an estimated wild population of less than 300 individuals.
TESF’s efforts to assist the USFWS in the recovery of black-footed ferrets began in 1998 with the construction of an outdoor preconditioning facility at Vermejo Park Ranch in New Mexico. Naive, cage-reared ferrets were placed into the outdoor pens where they were exposed to as wild an environment as possible while still being safely maintained in captivity. Ferrets in the outdoor pens lived in black-tailed prairie dog (C. ludovicianus) burrows and were routinely exposed to live prairie dog prey, as they honed their natural predatory instincts and prepared for life in the wild. Female ferrets were bred and soon thereafter whelped and weaned kits in the pens, all the while also being exposed to real prairie dog burrows and live prey. Ferrets that were preconditioned or born in outdoor pens and exposed to live prey have been documented to have higher post-release survival rates than those that have not. From 1999-2006, TESF preconditioned 393 ferrets at Vermejo.
From 2005-2007 at Vermejo Park Ranch and 2009-2011 at Bad River Ranches, TESF took the next step in preconditioning ferrets and initiated wild pre-conditioning projects at those ranches. At Vermejo, female ferrets and their kits were released onto a 1,000-acre prairie dog colony enclosed by electric netting which served to keep terrestrial predators – coyotes (Canis latrans) and badgers (Taxidea taxus )– away from the ferrets as they adjusted to life in the wild. At Bad River, the same procedures were followed without the use of electric netting. After a one to three month wild pre-conditioning period, the ferrets were captured and transported to permanent release sites. 48% of ferrets released at Vermejo and 48% at Bad River were recaptured and sent for permanent release elsewhere.
Despite our best efforts to establish ferrets at Vermejo that would contribute to federal recovery objectives – an effort that involved increasing black-tailed prairie dog acreage from 500 acres to over 10,000 acres and releasing 196 ferrets – it became clear from ferret survival rates over a 9-year period that it was unlikely that Vermejo’s black-tailed prairie dog colonies could support a stable ferret population. Although the ferrets generally did well on these colonies, with reproduction documented when spring precipitation was sufficient to support a robust prairie dog population, these good years were routinely offset by drought years in which prairie dog pup survival rates were below 10%, causing the ferret population to collapse. During these drought years, we documented the loss of all female ferrets and their kits, although male ferrets appeared to be largely unaffected. Due to the failure of ferrets to survive and reproduce during drought years and the likelihood that droughts will become more frequent and severe, in 2013 we decided to withdraw from ferret releases for the foreseeable future on black-tailed prairie dog colonies at Vermejo.
2012 marked the first year TESF began ferret releases on the Gunnison’s prairie dogs which occupy the high elevation mountain meadows of Vermejo. Historical records indicate 89% of the ferret specimens collected in NM were captured on Gunnison’s prairie dogs and one of the last specimens collected in the state was trapped on Vermejo at Castle Rock. Survival and reproduction rates of ferrets living on Gunnison’s colonies at Vermejo suggests a population of ferrets that meet de-listing requirements could be established, provided we are able to control sylvatic plague.
Project Activities in 2018
In 2018, the black-footed ferret population at Bad River collapsed in response to a plague epizootic which swept through the prairie dog population. The SPV applied in late 2017 was not effective in preventing or limiting the spread of the disease. In contrast, those areas dusted with Deltamethrin persisted through the epizootic. It remains unclear why the SPV failed to protect the prairie dog population, although the timing of the application may have been a factor.
Proposed Future Activities and Considerations
As demonstrated at Vermejo and Bad River, ferret recovery is inextricably linked to prairie dog conservation and active plague management. Currently there are two options available to mitigate the disease on prairie dog colonies: (1) dust the inside of prairie dog burrows with an insecticide (Deltamethrin) which kills fleas (which serve as the vector for plague) and (2) distribute the SPV on colonies to vaccinate the prairie dogs that eat the bait against the disease. In 2018, we employed both plague mitigation options on Turner properties with only the Deltamethrin application proving itself effective.
In 2019, we hope to participate in the production and field trials of a new plague mitigation tool called ‘FipBits’. FipBits will use the same bait matrix as the SPV, but instead of a plague vaccine the active ingredient in the bait will be fipronil (e.g., Frontline®). We hope to help with the production of FipBits by producing the bait in TESF’s Bozeman lab and to perform field trials at Bad River.