In my last column I cited figures given by the U.S. Fish and Wildlife Department on the number of wolves currently in the U.S. and referred to the oldest continuous study done on wolves and moose living on Isle Royale National Park (in Lake Superior). Moose are doing well, but the wolves are down to three and both their futures look grim in large part due to climate change.
In 1958 when the study began, the big question was whether wolf predation would significantly decrease moose population. During the decades since, the wolf population averaged between 18 and 27 and were organized into three packs. The moose usually averaged between 700 and 1,200. Since the study began, the moose population has collapsed twice. First in 1996 due to a severe winter their numbers fell from an all time high of 2,400 to 500. Then, after recovering, in the early 2000s they suffered series of hot summers which not only depressed their appetites but included tick outbreaks which further weakened them.
The wolves took advantage and their predation increased, but by 2006, with the moose not as plentiful, capturing them was difficult and one wolf pack after another failed. By 2011 the wolves were down to 9 in one pack and 6 in another that was socially disorganized. At that point only two females remained. The moose, however, rallied and as of 2015 their numbers are back up to 1,250. Climate and concomitant disease have clearly affected the rise and fall of the moose population. Not surprisingly, weather has played a significant role for the wolves as well.
The ice bridge that used to form regularly in winter between Canada and Isle Royale (7 times out of 10 during the 1960s, for example), now does so rarely (3 times in the last 17 years), and that prevents wolves who might want to find mates to start their own packs from leaving as well as “immigrant” wolves from arriving. Wolves don’t “choose” to inbreed, but because of circumstances, they have, and this has been detrimental to their health.
More than 30 dead wolves examined since 1994 show congenital anomalies of the spine. Of the three wolves left, two are middle-aged mates with their now only offspring, a pup slightly more than two years old who has a hunched posture and deformed tail. Their other two pups died before reaching age 2, and this pup isn’t expected to live long either.
A year ago, another wolf, “Isabelle,” left the island (via the ice bridge) in search of a mate but was killed within days by a pellet gun. When her body was examined, her teeth showed a “lifetime of stress.” Both lower canines had been broken off and then heavily worn. There was chronic infection affecting the dorsal incisors, resulting in increased nasal bone porosity. All teeth had noticeable flaking and sloughing off of enamel, especially on the dorsal canines.
The three remaining wolves need what’s called “genetic rescue” (mating with others they’re not related to), but it’s doubtful that’s going to occur in time. And the superintendent of the island, Phyllis Green, says her latest climate report indicates moose there may not even survive the next 50 years despite the fact moose population is up, seemingly a good thing, but with no wolves it’s going to result in long-term damage to the vegetation of the island, and ultimately to the moose themselves.
Ursula Carlson, Ph.D. is professor emerita at Western Nevada College and references the “Ecological Studies of Wolves on Isle Royale Annual Report 2014-15” by John A. Vucetich and Rolf O. Peterson for this column.
