Yellowstone National Park Wolf Population Numbers Down

Mollie's pack, which lives in the interior of Yellowstone and which has learned to prey on bison as well as elk, contains the highest number of wolves for a pack in the park, with 19 at the end of last year. NPS file photo by Doug Smith.

Wolf numbers in Yellowstone National Park at the end of 2011 were far off their peak of 174 counted back in 2003, a decline attributed to disease and a smaller prey base.

By the end of last year, biologists said there were at least 100 wolves -- 98 in 10 different packs, and two lone wolves, according to the annual report filed by the U.S. Fish and Wildlife Service.

"This suggests a long-term lower population equilibrium for YNP wolves, especially on the northern range," the report noted. "Northern range wolves have declined 60 percent since 2007 compared to only 23 percent for interior wolves during the same period. Northern range wolves are much more dependent on elk as a food source compared to interior wolves, which prey on elk and bison which are still widely available."

Though the report didn't specify the current size of the Northern range elk herd, at the end of 2006 the herd was estimated at 6,738 animals, while at the end of 2010 it was pegged at fewer than 4,700.

The annual report also noted that "disease impacts have also likely played a larger role in the wolf decline on the northern range because of higher canid density (wolves, coyotes and foxes) compared to the interior where canid densities are lower. The severity of mange continued to decline in 2011, although some packs still showed signs of the mite," the report stated.

Packs ranged in numbers of animals from three in the Agate Creek pack, to 19 in Mollie's (which lives in the park's interior), though the average pack size was right around 10 animals.

Two packs were lost in Yellowstone last year, though one was replaced by a pack from outside the park, the report said; the Quadrant Mountain pack was lost, but was replaced by the 8-mile pack, while the Grayling pack was lost without replacement (the Madison pack was not considered a Yellowstone pack although they did spend time in the park).

At least nine of the ten packs in the park had pups last year. The status of the Bechler pack was unknown. "The average number of pups/pack in early winter was 4.1, slightly lower than the 2010 average of 4.8 pups/pack, but higher than 2009 (3.8)," the report noted. "A total of 34 pups in Yellowstone survived to year end, four less than in 2010."

Ten radio-collared wolves died in Yellowstone died last year, with "intraspecific competition" -- wolf-on-wolf attacks -- accounting for 60 percent of all documented mortalities (four were from the Agate Creek pack). "One wolf died from a collision with a vehicle, another from an elk or bison, one from legal human harvest (park wolf outside the park borders), and one was illegally killed," the report noted.