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Isle Royale National Park's Wolf Population Loses Two Packs, Moose Population Steady
Within her den, the she-wolf was giving birth to a large litter, enough pups to not just bolster the size of the East Pack that long had ruled the eastern side of Isle Royale, but make it the largest pack on the Lake Superior island.
But something went wrong last April when the middle-aged female, whose mate hadn't been seen for months, was whelping. For some reason her uterus stopped contracting and she died, as did the eight pups she was carrying. A healthy litter would have pushed the East Pack, a presence in Isle Royale National Park for nearly four decades, one that long had dominated the park's wolf hierarchy, back to the top, numerically at least.
Instead, her death and that of her pups completed the collapse of the East Pack, which was the latest in a long lineage of packs that had claimed that side of Isle Royale since 1972.
Until 1995, when wolves were returned to Yellowstone National Park, those that roamed Isle Royale had been the most-studied in the United States, as researchers had been following the island's wolves since 1959. While Isle Royale's wolves still retain the record for most continuous study, the Yellowstone wolves have eclipsed them in popularity. Not only have tens of thousands of Yellowstone visitors been able to watch -- not just glimpse, but watch for substantial periods of time -- wolves, but those wolves have been highly visible to researchers thanks to the openness of Yellowstone's landscapes and to access to that landscape.
At Isle Royale, wolves lope through thick forests that swallow them up visually, and researchers don't benefit from roads that circle and even bisect wolf territories. In Yellowstone, wolves can be watched year-round as they roam through the sprawling Lamar River Valley.
"We routinely watch them from the road," Dr. Doug Smith, who oversees Yellowstone's wolf program, said earlier this year of the observations he's been able to make.
"We’ve seen hundreds of attacks. Most people in other areas have seen two or three. Rolf Peterson, who’s been studying wolves for 40 years (on Isle Royale), has seen 12 kills in his life," said Dr. Smith. "We’ve seen pushing 100 (kills) and probably 300 or 400 chases. How do they interact with coyotes and grizzly bears? Those are things that you (normally) gather data on indirectly. We’re watching them!"
Yellowstone's packs, like those of Isle Royale, rise and fall through the years. But compared to Isle Royale's wolf population, Yellowstone's is substantial, containing perhaps at least 100 individuals going into the current denning period. Isle Royale's population peaked at about 50 animals in 1980, when an estimated 1,000 moose lived on the island. Times now, though, are lean for island's wolves, and the loss of the East Pack, along with the disappearance of the Paduka Pack, both cut in half the number of packs that roam Isle Royale and dropped the number of individuals there to just 19 at the end of 2009.
Still, Dr. Peterson isn't worried that Isle Royale soon will be without the predators.
“Not because of these fluctuations. A couple of years ago I wondered, 'We don’t have enough moose for four packs. We don’t have enough for two,'" he recalled Friday.
But then, of course, the prey base collapsed, and soon on its heels so too did the number of predators.
In the 2009-2010 annual report on wolf research at Isle Royale (attached), Drs. Peterson and John Vucetich recount the demise of the East Pack and Paduka Pack and point to the bottoming out of the moose population. Once as high as 1,000 animals, the moose count at the end of 2009 was estimated at 530. While that's slightly more than half of the high point counted back in 1980, the researchers believe the moose population is set to rebound. Not only are wolf numbers down, but parasitic tick infestations that have bedeviled the moose for a decade have dropped somewhat.
“The foundation is set for them to increase now. Wolves had to decline before enough calves would make it through to allow the population to grow," said Dr. Peterson. "So the next two years will be interesting because we’ll see what kind of growth potential the moose population really has. There have been enough wolves to keep them down for several years, so we’ll see if they can increase now in spite of whatever the climate does.”
While the success of this spring's calving won't be known until a moose census is conducted next winter, already there has been at least one sign that, with the decline of wolves, the moose are poised to have a population explosion of some size.
“If we see calve twins all over the place this summer, then that’s an early indicator. But it doesn’t give us any annual number to hang onto," said Dr. Peterson, who added, though, that "The only twins we did see this year were at the extreme northeast end where the wolves are gone. It’s unusual for a set of twins to make it through the winter if there are wolves around.”
But the death of the East Pack alpha female, which had had an incestuous relationship with an uncle that produced three litters, and similar behavior noted among Isle Royale's other wolves, raise some questions about the long-term viability of the island's wolves. While researchers were not able to pinpoint what caused the female's contractions to stop, there are suspicions that inbreeding might have contributed to that. Too, the alpha female and male of the Paduka Pack were sister and brother.
Dr. Peterson wouldn't fully attribute the demise of the two packs to inbreeding, but believes it played a role.
“The immediate effect (of the East Pack's demise) was the female died, and her whole litter died with her. Had she lived and had eight pups, I think they’d still be there today in some form," he said. "So why did she die? That’s an unanswerable question, because we don’t know. I mean, we just don’t have any way to determine that. If we’d seen her die and gotten blood samples at that point, maybe a diagnostic lab would have been able to figure something out."
Literature indicates that, among dog breeds, inbreeding can lead to "uterine inertia," or the halting of contractions, but it hasn't been documented among wolves, the wildlife biologist said.
"It’s just a guessing game. It is extremely unusual for wolves. I don’t know of any other cases," he said.
And though inbreeding long has been observed among Isle Royale's wolves, how great a problem it is with the packs' long-term vigor is inconclusive, said Dr. Peterson.
“It’s been a background discussion among people. Whether it’s a problem for the wolves or not is up for debate. And that’s why it has been a background discussion for a long time," he said. "There’s no question they’re heavily inbred. We’ve known that ever since we really started looking at their genetics, starting about 20 years ago. But they’re still there, they’re still reproducing, this female had eight pups. That’s remarkably good. And so there’s no detectable population-level effects of inbreeding that are clear. So far.”
Perhaps an equal if not more pressing problem for the wolves and moose of Isle Royale is that funding to support the research performed by Drs. Peterson, Vucetich, and their colleagues long has been waning.
“The National Science Foundation has given us a flat budget for ten years, and the National Park Service has given us a flat budget for 35 years. Right there is the problem,” said Dr. Peterson. "Costs keep going up, the available support is flat at best. We’re constantly looking.”
To donate, visit http://www.isleroyalewolf.org
|ISRO-2009 Wolf Report.pdf||1.59 MB|