The Wolves of Isle Royale
Air Date: Week of April 5, 1996
Steve Curwood speaks with biologist, photographer and author Dr. Rolf Peterson about his research and recent book The Wolves of Isle Royale: A Broken Balance. Moose are also prominent on the island and in Peterson's research.
CURWOOD: America's Isle Royale National Park is a forested gem set far north in Lake Superior, just 20 miles from the Canadian shore. At the turn of the century, moose arrived on Isle Royale, probably by swimming from the mainland. They had no natural predators until about 50 years later, when a single pair of gray wolves apparently walked to the island across an ice bridge. And so began a simple arrangement. It's a perfect place to study nature's balancing act. Dr. Rolf Peterson is a wildlife biologist and accomplished photographer who studied wolf-moose dynamics on Isle Royale for 25 years. He's trying to find out just how many moose and wolves the island can sustain. He's captured the wonder of the place in a new book from Willow Creek Press. It's called The Wolves of Isle Royale: A Broken Balance. Dr. Peterson, on the cover of your book, there's a picture of a wolf howling at the moon. Is that a photograph you took?
PETERSON: It's a painting, but of a real wolf.
CURWOOD: The wolf's name was?
PETERSON: Well, we called him Murphy, just because he got, everything seemed to go wrong for this wolf, and he ended up the last 4 years of his life living as a lone wolf who didn't do real well, but he got by. But never succeeded in breeding, and got chased -- he could kill moose by himself but he usually got chased off these kills by territorial packs. So he suffered a rather obscure end and died of starvation.
CURWOOD: And what did he sound like? I see he's got his head tossed back, you know his throat is open.
PETERSON: Well, I'm not sure this particular wolf ever howled, because lone wolves typically try and remain as hidden as possible. Just getting by, basically. But the normal wolf howl is a pretty deep, throaty sound with a lot of variability. And they can communicate pretty complex messages.
CURWOOD: Think back to a situation where you heard a wolf howling, and give me that howl, and tell me the context of it after we hear it.
PETERSON: Let's see if I can imitate it first. (Howls) That's a pretty pathetic howl, but it's one that we actually observed. A male and female dominant, alpha individuals in a pack, and the mother and father in other words of most of the other wolves in the pack. And it was summer time, and they came home to where their pups were parked in the woods, near a den site, and found everybody gone. And so they sat down and immediately the male started out howling, and then the female came in at a higher pitch, and they howled for 2, 3 minutes. And then we could just barely pick out with our own ears a response several miles away, where the pups had been moved by some babysitters. So the wolves had their information and they up and left, and we never saw them again at that site.
CURWOOD: Now the balance of wolves and moose on this island is constantly changing. Can you tell me a bit about the various booms and busts that we've seen over the decades?
PETERSON: Of course the first major one was moose, when there were no wolves present. There was a big food crash in the 30s. And then once wolves were in place in the 1950s the amplitude of changes in moose numbers hasn't been smoothed out by wolf predation. And in a very real sense the wolves protect the food base of moose and help perpetuate it, because moose have the capacity to destroy their own food base.
CURWOOD: We need to talk about the basic ecology here. If wolves eat the moose, the moose eat --
PETERSON: They eat trees and shrubs and aquatic plants in summer time. But it's the winter browse, the plants that they eat in winter, that is most limiting. And in recent years there have been so many moose that very little of that forage is available even by midwinter. So a lot of malnutrition has set in, and of course this winter was a winter to set records in terms weather and snow depth, and a lot of moose simply didn't make it.
CURWOOD: So it was a pretty good winter, actually, if you were a wolf.
PETERSON: Oh certainly, yeah. A banner year for the wolves. They didn't have to work as hard because they often found moose that had starved to death, or many moose simply fell off cliffs while they were looking for something to eat. Literally, food was falling out of the skies. For the first year in almost a decade, all 3 packs had at least 1 pup survive until winter. Their numbers have been low for most of the last 15 years, and there's a sub-quest, we might say, we've been searching for the reason for their problems. Because they really have been on the edge of extinction. They reached the world's highest density of wolves in the wild in 1980 with 50 wolves present on this relatively small island, and 2 years later there was simply, there were just 14 left.
PETERSON: So over 4 dozen wolves had died in that 2-year period.
CURWOOD: What caused that, do you think?
PETERSON: Well initially we attributed it to the shortage of food, because they had pretty much cleaned out of the moose population the animals that were vulnerable to predation. But now we look back and realize there were some disease events coming through the Midwestern states, and Isle Royale specifically. Canine piro-virus probably led to that big crash in 1980 to '82. This is an exotic virus, a new mutant virus that people probably brought to the island inadvertently.
CURWOOD: But things have turned around recently.
PETERSON: In 1996 there are 22 wolves present, so they're up out of the real danger zone.
CURWOOD: So do you think this means that the system is now righting itself, that the wolves will survive?
PETERSON: They have a good chance at survival. I'm not sure I would call them completely recovered because they do have a genetic heritage now that could certainly put them at risk if theory is right. It looks like all the wolves have descended from a single female, probably a founder of the population in the 1940s, and they're all essentially related like brothers and sisters and they've lost significant genetic variability. And we'll see if they can get around the theoretical risks of genetic decay that we seem to be preoccupied with in endangered species management
CURWOOD: Rolf Peterson is a wildlife ecologist at the Michigan Technological University. His new book is called The Wolves of Isle Royale: A Broken Balance. Thank you, sir.
PETERSON: You bet. Thank you.
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