Wolf Information Continued
Wolves are highly social animals and live in packs. Worldwide, pack size will depend on the size and abundance of prey. In Yellowstone, average pack size is 10 individuals. The pack is a complex social family, with older members (often the alpha male and alpha female) and subordinates, each having individual personality traits and roles within the pack. Packs defend their territory from other, invading packs by howling and scent marking with urine.
Wolves consume a wide variety of prey, large and small. They efficiently hunt large prey that other predators cannot usually kill. In Yellowstone, 90% of their winter prey is elk; 10–15% of their summer prey is deer. They also can kill bison.
Many other animals benefit from wolf kills. For example, when wolves kill an elk, ravens arrive almost immediately. Coyotes arrive soon after, waiting nearby until the wolves are sated. Bears will attempt to chase the wolves away, and are usually successful. Many other animals—from magpies to invertebrates—consume the remains.
Changes in Their Prey
From 1995 to 2000, in early winter, elk calves comprised 50% of wolf prey and bull elk comprised 25%. That ratio reversed from 2001 to 2007, indicating changes in prey vulnerability and availability. The discovery of this change emphasizes the importance of long-term monitoring to understand predator-prey dynamics. Changes in wolf predation patterns and impacts on prey species like elk are inextricably linked to other factors such as other predators, management of ungulates outside the park, and weather (e.g. drought, winter severity). Weather patterns influence forage quality and availability, ultimately impacting elk nutritional condition. Consequently, changes in prey selection and kill rates through time result from complex interactions among these factors. Current NPS research focuses on the relative factors driving wolf predation over the last two decades.
In the first years following wolf restoration, the population grew rapidly as the newly formed packs spread out to establish territories with sufficient prey. The wolves have expanded their population and range, and now are found throughout the Greater Yellowstone Ecosystem.
Disease periodically kills a number of pups and old adults. Outbreaks of canine distemper have occurred in 2005, 2008 and 2009. In 2005, distemper killed two-thirds of the pups within the park. Infectious canine hepatitis, canine parvovirus, and bordetella have also have been confirmed among Yellowstone wolves, but their effect on mortality is unknown.
Sarcoptic mange, an infection caused by the mite (Sarcoptes scabiei), reached epidemic proportions among wolves on the northern range in 2009. The mite is primarily transmitted through direct contact and burrows into the wolf’s skin. This process can initiate an extreme allergic reaction and cause the wolf to scratch the infected areas, which often results in hair loss and secondary infections. By the end of 2011, the epidemic had mostly subsided; however, the infection is still currently present at lower prevalences throughout the park.
Wolf packs are highly territorial and communicate with neighboring packs by scent-marking and howling. Occasionally packs encounter each other and these interactions are typically aggressive. Larger packs often defeat smaller groups, unless the small group has more old adult or adult male members. Sixty-five percent of collared wolves are ultimately killed by rival packs.
The park’s wolf population has dropped substantially since 2007, when the count was 171. Most of the decrease has been in packs on the northern range, where it has been attributed primarily to the decline in the elk population and available territory. Canine distemper and sarcoptic mange have also been factors in the population decline.
Each year, park researchers capture a small proportion of wolves and fit them with radio tracking collars. These collars enable researchers to gather data on an individual, and also monitor the population as a whole to see how wolves are effecting other animals and plants within the park Typically, at the end of each year, only 20% of the population is collared.
Wolves in the Northern Rocky Mountains have met the US Fish and Wildlife Service’s criteria for a recovered wolf population since 2002. The US Fish and Wildlife Service in 2013 estimated about 1,592 wolves and 71 breeding pairs in the Northern Rocky Mountain Distinct Population Segment including areas of Idaho, Montana, and Wyoming.
The gray wolf was removed from the endangered species list in 2011 in Idaho and Montana but are currently protected as endangered species in the state of Wyoming. Wolves are hunted in Idaho and Montana under state hunting regulations. Learn More: Wolf Restoration in Yellowstone...
Interesting Wolf Behavior
Wolves kill each other and other carnivores, such as coyotes and cougars, usually because of territory disputes or competition for carcasses. In 2000, however, the subordinate female wolves of the Druid pack exhibited behavior never seen before: they killed their pack’s alpha female; then they carried her pups to a central den and raised them with their own litters.