ISLE ROYALE, Mich. (WJMN) — Michigan Technological University’s annual Isle Royale Winter Study found the island’s wolf population stable, while the moose population is experiencing a dramatic decline.
The study, now in its 65th year, was led by Sarah Hoy, John Vucetich and Rolf Peterson of Michigan Tech’s College of Forest Resources and Environmental Science. The researchers spent time on the island from Jan. 20 to March 3. Findings were released Wednesday.
Isle Royale’s wolf population is estimated at 31, primarily divided between an East Pack made up of 11 wolves and a West Pack of five wolves. A small pack in the middle of the island was also observed by researchers, newly developed in recent years since the others were established in 2019-20.
“Prior to the translocation of wolves to Isle Royale in 2018, the wolf population most commonly consisted of three stable packs and a small number of lone wolves,” Vucetich explained. “By contrast, over the past 12 months the population appears to be characterized by three to four reproducing groups, of which only two seem to have well-established territories, and many wolves that are not closely associated with an established pack.”
Peterson says that three or four wolf litters were born in the spring of 2022, most of which belong to the established packs. The West Pack is believed to have one litter, the East Pack with two and a probable litter born in the middle. Researchers say three pups survived the winter between the East and West packs, with more expected to be born in 2023.
“During the 2023 breeding season, we observed evidence of four, possibly five, breeding females,” said Peterson.
Researchers says the increase in populations is a promising development in reestablishing the island’s wolf population after no litters were observed between 2015 and 2018. The wolf population is believed to have collapsed during that time due to inbreeding.
After repopulation of the species in 2018, one litter was born in 2019, two litters in both 2020 and 2021 and four possible litters in 2022.
“The reproductive success of the wolf population has steadily increased over the last five years,” Hoy said. “The majority of wolves in the population were all born on the island.”
Hoy added that indications show the continued viability of adult wolves on Isle Royale.
“Over the past year, the survival of adult wolves was slightly higher than the long-term average observed on Isle Royale,” Hoy said.
The study says that the average life expectancy of a wild wolf is 4.5 years.
The reasearchers’ study of the islands moose population was much less positive, showing a continued year-over-year downward trend with a roughly 28% decline from the previous count. The overall counted population dropped from 1,346 to 967, largely due to food shortages on the island.
Hoy says the drop in count is comparable to the species’ population collapse that happened in the mid-1990s on Isle Royale. Since peaking at 2,060 in 2019, the moose population has decreased by 54%.
Researchers say that survival rates of adult moose have declined by 30% over the past four years, with a large drop-off in the number of calves born, as well. Historically, at least 13% of counted moose are calves, but decreased to just 2% in 2023, the lowest number ever recorded.
The two main factors in the population decline are starvation and predation by wolves. The study estimates that about 10% of the moose population was killed by wolves in the past year, a number that was expected following the reintroduction of wolves to the island. Starvation, however, caused a higher number of deaths than the wolves.
“For every moose we found that was killed by wolves, one to three other moose had died of starvation. Forty-six percent of the dead moose we examined over the past year died of malnutrition,” Peterson said, adding that the elevated starvation rates continue a pattern researchers first detected in 2019.
A food shortage, caused largely by overbrowsing and spruce budworm infestations of balsam fire saplings, is a main cause of the increased death rate. Both issues prevent saplings, the preferred winter food source for moose, from developing into mature, cone-producing trees.
“Over the past year, we observed that many balsam fir saplings had either died or had few green branches left,” said Hoy.
Researchers observed unusual behaviors, including moose stripping bark from mature aspen and balsam firs and evidence that moose are increasing browsing on other species of tree, such as cedar. Researchers say the behaviors suggest that foraging moose can’t find sufficient fir twigs and foliage during winter.
Moose on Isle Royale have a life expectancy of 10 years.
Researchers are now conducting summer fieldwork on the island.
“It’s remarkable to reflect on how much we’ve learned about these wolves and moose over the past six decades,” Vucetich said. “And, at the same time, how many more questions remain.”
You can read more about the wolves and moose living on Isle Royale here.