Black-footed Ferret (Mustela nigripes) Recovery Update

Mike Lockhart
Astrid Vargas
Paul Marinari
Pete Gober
National Black-footed Ferret Conservation Center, 410 Grand Ave., Suite 315, Laramie, WY 82070.

In 1998, the number of black-footed ferrets (ferrets; Mustela nigripes) produced from Species Survival Plan (SSP) captive breeding facilities (six zoos and one government breeding center) far surpassed all previous years with a total of 425 born and 321 ferret kits surviving to weaning.  The largest contribution of ferrets came from the U.S. Fish and Wildlife Service's (FWS), National Black-footed Ferret Conservation Center (NBFFCC) where 249 kits were born and 191 survived.  Record production was also achieved at the Phoenix Zoo and the Toronto Zoo.  Higher birth rates resulted, in large part, from the discovery of a principal cause of false pregnancy in ferrets by the National Zoo's Conservation Research Center; a problem that has long affected captive breeding efforts (Howard et al. 1998; Wolf et al. 1997).  Because female ferrets are induced ovulators, pairings with males that lack viable sperm result in false pregnancies.  It was discovered through electroejaculation techniques that many juvenile males that display physical signs of breeding readiness (by standard testes measurements) are aspermic until later in the season.  By utilizing only males with demonstrated sperm quality (via electroejaculation), the number of pseudopregnant females at the NBFFCC dropped by 20 percent.  The FWS has recommended that this monitoring technique be implemented as a program-wide management tool at SSP facilities in 1999.

A total of 217 kits were allocated for reintroduction and field breeding programs in 1998.  Ninety-four (59.35; i.e., 59 male and 35 female) ferret kits were provided to the Conata Basin/Badlands National Park reintroduction area in South Dakota.  Seventy-seven ferret kits were allocated to two separate release sites on a Montana experimental reintroduction area; 55 kits (35.20) to the Ft. Belknap Indian Reservation and 22 kits (11.11) to the Charles M. Russell National Wildlife Refuge.  Finally, 29 kits (18.11) were sent to Arizona, some of which will be released while some will be retained for on-site breeding efforts in 1999.  Ferrets are also being provided to two new field breeding projects: Seven kits (4.3) will be transferred to a New Mexico breeding facility constructed by the Turner Endangered Species Fund; and 10 kits (5.5) will be sent to a breeding project on an experimental reintroduction area in northwestern Colorado and eastern Utah.

As was the case last year, all ferret kits destined for release in the wild in 1998 were "preconditioned."  Preconditioning consisted of extended exposure to outdoor pens that have naturalistic prairie dog burrows, and in which developing kits are exposed to prairie dog prey (Vargas et al. 1996).  Preconditioning significantly enhances the survival of ferrets released to the wild (Biggins et al. 1998).  With construction of 24 on-site preconditioning pens by the U. S. Forest Service in South Dakota in 1997, the national program now has sufficient capacity to precondition all ferrets targeted for release.

News regarding ferret production in the wild in 1998 is also highly encouraging.  Of 56 adult ferrets (25.26, 5 sex undetermined) found during spring surveys in South Dakota, more than 70 kits have been observed.  Of 25 adults (5.20) located last spring in Montana, at least 31 different kits have been detected.  So far, it appears that litter sizes are also larger than past years.  Between both South Dakota and Montana over 34 litters and more than 100 wild born young have been produced in 1998.

Significant progress in the area of on-site breeding was also achieved this past spring in Arizona.  The Arizona Game and Fish Department produced 26 kits (of which 18 survived) in 1998.  This marks the first time that ferrets were produced in on-site pens at an existing reintroduction area.  A portion of the kits will be released from their pens directly to the wild while others will be retained for future breeding efforts.
Although field surveys and reintroduction efforts are still ongoing at the time of this report, 1998 can be considered to be the most successful year in the history of the ferret recovery program.  Given the number of ferrets that persisted from previous reintroductions, the number of kits produced in the wild, and the number of ferrets released in 1998, it is likely that more ferrets will exist in the wild during the fall of 1998 than are in captivityˇan important program milestone.  Captive breeding and reintroduction capabilities continue to steadily improve.  Little progress, however, has been made in the conservation of prairie dog habitats upon which black-footed ferrets depend.  A recent evaluation by the FWS indicated that only ten sites exist in all of North America that have prairie dog complexes of sufficient size and density to potentially support viable ferret populations (which include all current reintroduction sites).  The most formidable challenge now facing ferret recovery is whether suitable prairie dog habitat can be secured to achieve the objectives of establishing multiple, self-sustaining ferret populations in the wild.

Literature cited

Biggins, D., J Godbey, L. Hanebury, P Marinari, R. Matchett, and A. Vargas.  1998.  Survival of Black-footed Ferrets.  Journal of Wildlife Management 62:643-653.

Howard, J.G., K.N. Wolf, P.E. Marinari, J.S. Kreeger, T.R. Anderson, A. Vargas and D.E. Wildt.  1998.  Delayed onset of sperm production in 1-year old male black-footed ferrets.  Proceedings: Society for the Study of Reproduction, Supplement 58:124.

Vargas A, M. Lockhart, P. Marinari, and P. Gober.  1996.  The Reintroduction Process:  Black-footed Ferrets as a Case Study.  Pages 829-834 in Proceedings: American Zoo and Aquarium Association Western Regional Conference, May 15-19, 1996, Denver, Colorado.

Wolf, K.N., D.E. Wildt, A. Vargas, P. Marinari, L. Williamson, M.A. Ottinger and J.G. Howard.  1998.  Compromised reproductive efficiency in male black-footed ferrets.  Journal of Andrology, 1998 Supplement: 44.

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