n the first years after restoration began in Yellowstone in 1995, the wolf population grew rapidly as the newly formed packs spread out to establish territories with sufficient prey, primarily elk. The wolves have expanded their population and range, and now are found throughout the Greater Yellowstone Ecosystem.
Disease periodically kills a number of pups. The first serious outbreak was 1999, then six years later in 2005. That year, distemper killed two-thirds of the pups. The next outbreak was just three years later, in 2008, when all but 22 of the pups died. This shortened interval concerns scientists. Infectious canine hepatitis, canine parvovirus, and sarcoptic mange also have been confirmed among adult wolves, but their effect on mortality is unknown.
Adult wolves kill each other in territory disputes. Such disputes happen each year, but increase when food is less abundant. This may have been why so many adult wolves died in fights during 2008. That year, scientists also found two wolves whose deaths were partially due to starvation.
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 there. Disease, primarily distemper and possibly mange, have also been factors in the population decline. In most years, park staff attempt to fit enough wolves in the park with radio collars to keep track of each pack for research and management purposes. Though the number varies each year depending on population size, typically 30 percent of the population is collared by the end of the collaring season.
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 2011 estimated about 1,650 wolves, 244 packs, and 110 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. Wolves are now delisted throughout the northern US Rocky Mountains, including Wyoming. For the first time since restoration, wolves are hunted in each state surrounding Yellowstone.