Warm Temperatures Disrupt Wolf-Moose Studies At lsle Royale National Park

Warm weather forced a halt in this winter’s study of wolves and moose at Isle Royale National Park/National Parks of Lake Superior Foundation file

Unseasonably warm temperatures led to a halt this past week in this winter’s study of wolves and moose at Isle Royale National Park as weak ice conditions made it too dangerous to try to land planes there.

“We were out there for about two weeks,” Sarah Hoy, a research assistant professor at Michigan Technological University involved with the study, said Friday during a phone call. “It’s just very unusual to have such a prolonged period of above-freezing temperatures.”

The warm spell — temperatures were running about 20 degrees above normal, according to the National Weather Service — disrupted the world’s longest-running study of prey and predators, one that dates to 1959. It did not entirely deprive Hoy and her colleagues of data on how the wolves and moose are faring on the Michigan island in Lake Superior, though.

While the data has yet to be analyzed, “we managed to complete our annual moose census,” said Hoy. “Every year we fly all over the island and count the number of moose that we see on different survey plots. So we should be able to get an estimate of moose population size, and recruitment. … And we did get some good, useful observations of the wolves, but to get more reliable information about the wolves and to see what’s going on during the breeding season, we really would have liked to have been out there a little bit longer and continue to monitor the wolves.”

The study nearly ended in 2018, when just two wolves were known to exist on Isle Royale. Chronic inbreeding had impacted the health of the population. While there was hope that “ice bridges” that formed between the Lake Superior island and the Canadian mainland during the winter of 2013-14 would enable wolves to arrive from Canada with new genes, no new wolves reached the island that winter, while one female left and was killed by a gunshot wound in February 2014 near Grand Portage National Monument.

Worries that the lack of an apex predator would lead to a boom in the moose population that in turn would over-browse island vegetation led to a 2018 decision to bring up to 30 wolves to the island. Some came from Minnesota, some from Canada. The move, then-Isle Royale Superintendent Phyllis Green said at the time, was not viewed as genetic rescue, but rather “about population management.”

In the end, 19 wolves were taken to the island, and they seemed to benefit from the high moose population.

A Great Lakes wolf’s average weight is 50-70 and 60-80 pounds for an adult female and male, respectively,” park wildlife biologist Mark Romanski noted in April 2022. “In spring 2021, an adult male weighing 94 pounds, and his offspring, two males and one female, weighing 85, 74, and 64 pounds were captured.”

The most recent population tally, made during the 2022-23 winter survey, indicated a wolf population of 31 individuals, an 11 percent increase from the previous year. The wolves were contained in three packs, one on the eastern end of the island, one in the middle, and one on the west end.

The moose population, meanwhile, had dipped to 967 individuals, a 28 percent drop from the 2021-22 estimate of 1,346. That 2022-23 count also represented a roughly 50 percent drop from the island’s peak estimated moose population of 2,000 seen in 2019.

Wolves weren’t solely responsible for the decline, though. Disease also played a roll, and starvation.

“Moose really struggled to find enough food this past winter,” Hoy, who has been working with wildlife biologists Rolf Peterson and John Vucetich on the wolf-moose studies, said in 2021. “Because there have been such large numbers of moose on the island over the last five years and moose ate branches faster than the trees can recover and replace them, the amount of food available to moose during winter has been getting progressively worse each year since 2017.”

“[Moose] can eat up to 40 pounds of vegetation a day, and so they can really start to impact the vegetation,” Hoy said Friday. “For the last couple of years, we’ve seen a lot of moose that had died from starvation.”

Indeed, of the 76 moose found dead during the winter and spring of 2022, necropsies indicated that nearly half [46 percent] had starved to death. Of the moose that died the previous year, 30 percent had starved. A typical year would see fewer than 5 percent of deaths attributed to starvation in the park.

In addition, ticks have been a significant problem for the moose. Following the winter of 2020-21 researchers saw “moose with very little fur left in spring — having scratched or bitten off almost all of their winter coats in an effort to rid themselves of the blood-sucking parasites. This is significant because blood loss to ticks can exacerbate the detrimental effects of food shortage. Despite the mild winter, depleted food supplies and ticks made life harder for the island’s moose this year,” a release that year from Michigan Tech noted.

Unless the weather turns more seasonal and allows for the biologists to return to Isle Royale, it could prove to be impossible this year to attach a solid estimate to the wolf population. Winter’s snows allow for the biologists to fly over the island and both track wolves and see where they’ve been, while the reduced tree cover allows for better population estimates. Estimates to wolf offspring following the upcoming mating season, however, could be possible this summer through genetic analysis of scat.

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