Against All Odds
North America’s Conservation “Long Shot” Now Vies for “Favorite” Status
Text and photographs by
Joanne Luyster, Keeper II
Black-footed ferrets (BFFs), long considered one of North America’s most endangered mammals, were reduced to only 18 animals in 1987. Faced with almost insurmountable odds, BFFs bounced back from the brink of extinction. By the end of 2006, the BFF recovery effort heralded three notable events:
More BFFs exist in the wild than in captivity.
Since 1999, there have been consistently more BFFs [600+] roaming the prairies at 18 reintroduction sites, from South Dakota to Mexico, than are housed in 6 captive breeding facilities [~270], including Louisville Zoological Garden (LZG)’s Conservation Center.
Significant numbers of BFFs are born in the wild annually.
In 2006, 400 kits were identified at reintroduction sites, primarily Conata Basin, SD, and Shirley Basin, WY. In fact, the Rosebud Sioux Reservation release site in SD translocated some of Conata Basin’s BFFs to initiate their wild population.
200+ BFFs sighted at Shirley Basin, WY. release site, which was abandoned in 1995.
Shirley Basin became the first BFF reintroduction site in 1991. However, no ferrets were released there after 1994 due to an outbreak of plague in the prairie dog population. Just eight ferrets were found in Shirley Basin 1996, and only four in 1997. Wildlife biologists did not survey the area for several years, but in 2002 they found 20 BFFs. In 2003, biologists launched an intensive survey of the site and they located and identified a minimum of 52 individual BFFs. Additional scientific work revealed that these BFFs, having been isolated from other BFFs, are slightly different genetically from the majority of the ferret population. In 2006,over 200 black-footed ferrets were found, making it the first or second largest release site.
These events become even more significant in the light of the obstacles facing ferret recovery.
When wildlife biologists assess the viability of conserving an endangered species, certain factors help predict whether or not a recovery effort may prove to be successful. In the case of BFFs, several factors appeared to doom the species:
Single prey species –BFFs prey almost exclusively on prairie dogs and are considered an “obligate” species, depending on prairie dogs for food as well as shelter. Prairie dogs are the keystone species of the short grass prairie ecosystem. But poisoning, disease, and habitat destruction have decimated the prairie dog population that once numbered over five billion animals.
Require specific habitat – BFFs live, sleep, breed, and feed in prairie dog burrows, and would therefore not easily adapt to another habitat. However, land cultivation and prairie dog eradication programs have reduced prairie dog habitat to only 1% - 2% of its former range.
Low genetic diversity- all known BFFs are descended from 7 founder members [only 7 of the 18 BFFs reproduced]. This small gene pool results in a less vigorous immune system in the ferrets, thereby making them more susceptible to endemic diseases such as canine distemper, which is essentially 100% fatal to BFFs.
Susceptibility to prey diseases- most predators are not susceptible to the same diseases as their prey. However, biologists discovered that BFFs can contract plague, a disease that has decimated prairie dog populations.
Usually this number of mitigating factors presents a grave prognosis for a recovery program. Yet BFFs appear to have overcome these obstacles and are well on the road to recovery.
BFF Recovery Synopsis
As many as 500,000 BFFs inhabit North American plains.
|1851||Audubon and Bachman publish description of a BFF, making it one of the last mammal species described in continental US.|
Federal government begins systematic prairie dog eradication programs.
|1943-1959||Only 70 BFFs sited during this period.|
|1964||Small colony of BFFs found in Mellette County, SD.|
|1966||BFFs placed on endangered species list.|
|1979||Last of 9 BFFs taken from SD population for captive breeding dies; SD population now extinct.|
|1981||Population of BFFs discovered in Meeteetse, WY; managed in wild.|
Wild population drops to 38 ferrets; begin capturing for captive breeding.
|1987||Last BBF, “Scarface” captured; captive breeding population totals 18 animals. Two litters bred in captivity, with seven surviving kits.|
BFFs sent to NZP-CRC and Henry Doorley Zoo for captive breeding.
|1991||Captive population over 200; first release Shirley Basin, WY. LZG and Cheyenne Mountain Zoo join captive breeding program.|
|1992||Toronto and Phoenix Zoos now part of captive breeding program.|
|1994||Reintroduction sites added in Montana and South Dakota.|
|1995||No ferrets released in Shirley Basin due to outbreak of plague in prairie dogs; biologists determine that BFFs also susceptible to plague.|
|1996||All BFFs slated for reintroduction receive preconditioning, greatly increasing survivability.|
|1997||First release on Native American lands (Fort Belknap, MT). Additional reintroduction sits added in Arizona, Colorado/Utah.|
|2000||SD reintroduction site produces enough wild births that it no longer requires additional allocations of BFFs. More BFFs living in wild than in captivity.|
|2001||Mexico reintroduction site added, making ferret recovery an all-encompassing North American effort.|
|2005||Intensive survey of Shirley Basin release site reveals 47 kits, 149 BFFs.|
|2006||400 kits born in the wild. Over 800 BFFs exist in the wild. 365 kits born in captivity.|
|2008||Total of 18 release sites established in US and Mexico. Plague hits Conata Basin site, reducing prairie dogs and BFFs.|
Grasslands National Park, Saskatchewan, Canada, becomes 19th reintroduction site.
For updates and additional information, check www.prairiewildlife.org
LZG’s Role in BFF Recovery
In 1991, few people had heard of, much less seen, a BFF when Louisville joined the recovery efforts. Then Director Dr. Bill Foster became aware of the ferrets’ dire plight in the late 1970’s and vowed that if the opportunity arose, he wanted the Zoo to play a role in the conservation of the BFF. So in 1991, LZG became one of 6 captive breeding facilities across North America. The first litter, born in 1992, also proved to be the most challenging for zoo staff. Dam (mother) “Julie” died when her five kits were 21 days old, and the staff had to hand raise the litter, a 24/7 feat not attempted before or since by any institution. Four of the five kits survived as well as nine other kits that year. Over the next few years, LZG managed to produce an increasing number of kits for the recovery program at a time when some of the other captive breeding sites experienced low productivity. As a result, LZG played an important role at a crucial time in BFF recovery effort, and continues to supply ferrets for this important conservation project. LZG BFFs have been released at all 18 reintroduction sites in US and Mexico. Biologists at the newly established Kansas release site found three litters produced by LZG BFFs in 2009.