Dennis Anderson
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Dennis Anderson

Renowned Minnesota wolf researcher Dave Mech was in his early 20s and a graduate student at Purdue University when he arrived on Isle Royale in 1958 to study the predator-prey relationship between wolves and moose. Mech’s three-year groundbreaking project detailed for the first time the killing efficiency of wolves and the vulnerability of moose on the 210-square-mile Lake Superior island.

Now in a compelling new book to be launched Tuesday titled “Wolf Island: Discovering the Secrets of a Mythic Animal,’’ Mech, along with Twin Cities co-writer Greg Breining, chronicles Mech’s life and times on Isle Royale — camping, hiking and observing from a single-engine airplane how wolves and moose interact in their constant struggle for survival.

Q What is unique about Isle Royale’s predator-prey relationship between wolves and moose?

A It’s the only place where there is one large prey animal and once predator. This is unique in the world. In summer on Isle Royale, the beaver comes into play as prey animal for wolves. But there are no deer, bears or caribou, for example, to complicate the study of wolf predation.

Q How many moose are on the island?

A During the three years I was there, between 500 and 600. Since then the herd has varied between 1,000 and 2,000.

Q What types of moose do wolves typically kill on Isle Royale?

A Wolves generally don’t take just any moose, a fact that has been demonstrated elsewhere as well. Most often, they end up with calves, older animals and moose that are debilitated due to parasites, broken bones or for other reasons. I was able to confirm this by aging the moose that were killed by wolves.

Q You followed a pack of 15 wolves throughout your three years of study. How frequently would that pack kill a moose?

A They were able to kill every few days. The density of moose on Isle Royale is probably the highest in the world, and in different settings wolves may have to hunt longer than that. A wolf can go months without eating. If they can’t find a prey animal near them, they will continue to search far and wide. Wolves also will cache parts of a kill to eat later. Sometimes they bury food a mile from a kill and dig it up when they need it.

Q Killing a moose every few days or so seems to indicate a high degree of predator efficiency.

A In fact, only about 7% of hunts by wolves were successful. This rate applies to winter hunts. Even after all these years, we’re not sure of the success rate of summer hunts.

Q How do moose fend off an attack by 15 wolves?

A Usually, by just standing their ground. If a moose is healthy and just stands there and defies the wolves, the wolves will often give up. In that case, there’s not a lot of kicking by the moose. If a moose runs, wolves have a better chance, even though the moose is kicking with his rear legs and swatting with his front hooves.

Q Visitors to Isle Royale today see a heavily forested island. But when you were there the island was much more open, which helped you see wolf interactions with moose by airplane that likely aren’t possible today, due to tree cover.

A The vision I had from the air watching wolves hunting moose couldn’t be replicated by researchers who came after me on the island. However, radio tracking started in 1968, and that offered new research opportunities.

Q How long will a pack of 15 stay on a moose carcass?

A About three days, though a smaller pack would stay longer. The first three days, they eat the intestines, muscles and organs. After that they’re down to the bones and chewing on the hide. Eventually, by the fourth day, it’s time to go. Once they leave a kill, they are hunting again.

Q You note in the book the frequent presence of ravens on wolf-killed moose.

A Some studies indicate as much as 25% of a wolf kill is consumed by ravens.

Q Fifteen wolves constitutes a larger pack than typically is seen in northern Minnesota.

A Correct, but we do see some packs in Minnesota that large. On Isle Royale, it remained a mystery why the pack I followed stayed at that number for three years. Why didn’t the pack get bigger? Why didn’t I find dead wolves? We know wolves have a litter every year. If I had been able to radio collar the pack, or some of them, we would have learned more.

Q What were the reasons for the wolf collapse on Isle Royale in 2015, and the need for new wolves to be brought to the island?

A Two basic reasons: 60 years of inbreeding took its toll, and about 10 years ago, when the island’s wolf population was down to 10 or so, three individuals, including a breeding pair, fell through the ice of an old mine pit. The population never rebounded.

Q Your study and subsequent studies show that predator-prey relationships are complex and depend on a number of factors, some of which aren’t easily understood. Winter weather, for instance, affects the hunting efficiency of wolves.

A Winter weather in large part determines the proportion of prey animals that wolves can kill. Mild winters are hard on wolves. Severe winters, conversely, can be pretty good for wolves and not for moose or deer. Global warming, we believe, also has an impact, due to changing landscapes and increasing numbers of ticks, which can impact moose.

Q Wolves have been a primary predator of moose calves in northeast Minnesota, where moose have been declining. Are moose in the northeast doomed to the same fate as northwest Minnesota wolves, which are essentially gone, and if so, will wolves be responsible?

A Wolves in the northeast began building up in the early 2000s and by 2006 had reached the highest density we have seen. All along, they were feeding on moose and deer, and by then were taking a fair number of moose calves. Moose numbers subsequently dropped until about 2013, and as they did, wolves dropped, too, in that area. Now they both have stabilized at a lower level. This same cycle has probably played out many times over many years, but science hasn’t paid much attention to it.

Dennis Anderson • danderson@startribune.com