WOLVERINE
Photo Credit: Steve Kroschel
The wolverine is the largest terrestrial member of the family Mustelidae. Adult males weigh 12 to 18 kilograms (26 to 40 pounds) and adult females weigh 8 to 12 kilograms (17 to 26 pounds). The wolverine resembles a small bear with a bushy tail. It has a broad, rounded head; short, rounded ears; and small eyes. Each foot has five toes with curved, semi-retractile claws used for digging and climbing.
In North America, wolverines occur within a wide variety of habitats, primarily boreal forests, tundra, and western mountains throughout Alaska and Canada; however, the southern portion of the range extends into the contiguous United States.
Currently, wolverines appear to be distributed in two regions in the lower 48 states: the northern Cascades in Washington, and the northern Rocky Mountains in Idaho, Montana, and Wyoming. Wolverines were extirpated in historical times from the Sierra Nevada and the southern Rocky Mountains.
Research indicates that wolverines either did not exist as established populations or were extirpated prior to settlement and to the compilation of historical records in the Great Lakes region, possibly due to climate changes that occurred through the 1800s and 1900s. The widely scattered records from this region are consistent with dispersing individuals from a Canadian population that receded north early in the 1800s. The possibility that wolverines existed as established populations prior to the onset of trapping in this area cannot be ruled out, but we have no evidence that they did. No evidence in the historical records suggests that wolverines were ever present as established populations in the Great Plains, Midwest, or Northeast.
The delineation of wolverine historical and present distribution is inherently difficult for several reasons. Wolverines tend to live in remote and inhospitable places away from human populations. Wolverines naturally occur at low densities and are rarely and unpredictably encountered where they do occur. Wolverines often move long distances in short periods of time when dispersing from natal ranges, making it difficult or impossible to distinguish with confidence between occurrence records that represent established populations and those that represent short-term occupancy without the potential for establishment of home ranges and reproduction. These natural attributes of wolverines make it difficult to determine their present range, or trends in range expansion or contraction that may have occurred in the past.
Breeding generally occurs from late spring to early fall. Females undergo delayed implantation until the following winter to spring, when active gestation lasts from 30 to 40 days. Litters are born between February and April, containing one to five kits, with an average in North America of between 1 and 2 kits.
Female wolverines use natal (birthing) dens that are excavated in snow. Persistent, stable snow greater than 1.5 meters (5 feet) deep appears to be a requirement for natal denning, because it provides security for offspring and buffers cold winter temperatures.
Wolverines are opportunistic feeders and consume a variety of foods depending on availability. They primarily scavenge carrion, but also prey on small animals and birds, and eat fruits, berries, and insects. Wolverines have an excellent sense of smell that enables them to find food beneath deep snow.
Wolverines require a lot of space; the availability and distribution of food is likely the primary factor in determining wolverine movements and home range size. Wolverines travel long distances over rough terrain and deep snow, and adult males generally cover greater distances than females. Home ranges of wolverines are very large, but vary greatly depending on availability of food, gender, age, and differences in habitat. These home range sizes are large for mammals of the size of wolverines and may indicate that wolverines occupy a relatively unproductive niche.
Recent Actions: After a thorough review of all the available science, the Fish and Wildlife Service has determined that the contiguous United States population of wolverine should be protected under the Endangered Species Act (ESA). However, the rulemaking to propose ESA protections for the wolverine will be delayed while we work on listing proposals for other species in greater need. The wolverine will be added to the list of candidates for ESA protection. As a candidate species, the wolverine will not receive protection under the ESA; however, we will review its status annually and will continue to work with landowners and partners to implement voluntary conservation measures.
The results of status review indicate that climate warming is the primary threat to wolverine. Our evaluation found that the effects of climate warming are serious but so far have not resulted in any detectable population effects to the species. Because the threat of climate warming is not imminent, we will use our resources to work on listing determinations for species at greater risk of extinction.
- Press Release: December 13, 2010 Wolverine to be Designated a Candidate for Endangered Species Protection
- Federal Register Notice: December 13, 2010 12-month Finding on a Petition to List the North American Wolverine as Endangered or Threatened
- Questions and Answers
- Fact Sheet
- Photos on Flickr
