 Moose populations continue to increase at Isle Royale National Park despite efforts to control their numbers through the introduction of wolves. According to the latest annual report, moose (Alces americanus) numbers on the Michigan island in Lake Superior are up to 2,060 animals. Meanwhile, wolf (Canis lupus) numbers sit at 15 individuals after a number of new animals were introduced by the National Park Service in recent months. “They are self-organizing now, and nobody has any control over them,” said Rolf Peterson, a wildlife biologist at Michigan Technological University who worked on the survey as part of a collaboration between the college and the National Park Service. “What has to happen is for wolves to start to reproduce and organize into packs.” The wolves on the island, which lies just south of the Canadian border and 20 miles from the Ontario shore, have been a part of a saga. While the island used to connect with the mainland to the north most winters via an ice bridge that allowed new wolves to enter and bolster the Isle Royale population, warmer temperatures have blocked off new recruitment in recent decades. As the wolf population dropped, the moose population exploded, jumping up about 19 percent every year since 2012, including the most recent survey. Their overabundance resulted in the moose consuming saplings of balsam fir and other plants before they could, causing the forest canopy to suffer. Invasive grasses have begun to take over the area. The moose are even outcompeting beavers (Castor canadensis) for food. Meanwhile, the wolf problem came to a head in 2016, when only two closely related wolves remained on Isle Royale. A single pup, which was an offspring of the pair, died a year earlier, due possibly to health complications from inbreeding. The Park Service made a plan to restore 20 to 30 wolves to the island and brought the total population to 15, including the original two, over several successive introductions in recent months. Peterson said the moose population will likely continue to increase for the next few years due to past momentum. “The wolves will have an effect primarily by killing moose calves and decreasing the annual recruits,” he said, adding that the wolves will also start to take down more adults as they get weaker with age. The researchers found 10 moose were killed in February, an increase from the previous year, suggesting that the trend may start to reverse soon. “That’s what we’d expect wolves to do, and they are doing it,” Peterson said. Once the wolves start to form into packs, they will be able to take down more moose. He said the island can likely sustain three or four wolf packs. Researchers also fit 20 adult moose with radio collars to gain a better understanding of the population.
Copyright 2022 Learn By Doing, Inc. HOUGHTON, Mich. -- The lack of winter weather explains many of the changes in the annual wolf-moose survey at Isle Royale National Park, according to Michigan Technological University's Rolf Peterson.
Peterson, a professor of wildlife ecology at Michigan Tech, said the 2002 survey counted 17 wolves on the island, as opposed to 19 last year. The island's moose population increased from about 900 last year to 1,100 in 2002. "The significant factor was a lack of winter," Peterson said, referring to the very light snowfall this year. "Moose were in places where we don't normally see them in the winter--on hillsides and out of the conifer swamps." The Isle Royale wolf-moose survey is the longest running predator-prey study in the world, now in its 44th year. Peterson has conducted the study for the last 32 years. As an island in the middle of Lake Superior, Isle Royale presents a unique opportunity for such research. Peterson said the wolves suffered a mortality rate of almost 50 percent this winter and that last year's seven pups kept the population near steady. The Isle Royale wolves have formed three packs: the east pack with six members, the Chippewa Harbor pack with five, and the middle pack with four. There are also two single wolves unattached to a pack. Researchers confirmed a confrontation between the east pack and the Chippewa Harbor pack, with the east pack's alpha male killed. Peterson's team found that particular wolf, one of four on the island wearing a radio collar, just offshore in Lake Superior. "The Chippewa Harbor pack has been pushing the east pack aside and enlarging their territory," Peterson said. "A mild winter is always tough on the wolves, and this probably contributed to the confrontation. "We watched about 15 encounters between wolves and moose this winter," he said. "The moose were almost always intimidating, so the wolves didn't bother to attack." Typically the wolves prey on old moose and young calves. But with little snow cover, the moose could move more freely and avoid the wolves. "Last year, two-thirds of the kills were moose calves," Peterson said. "This year, it was about 20 percent. The wolves had to work hard to find a moose to kill." Peterson also said that all three packs had breeding activity, so he expects three litters of pups to be born in late April. While the moose have fared relatively well this winter, Peterson says they could begin to have problems this spring and summer. "The trend of warmer temperatures, and a warm, dry spring, could mean an increase in tick infestation of moose," he said. High winds in December also caused a large blow-down of the balsam firs on the western half of the island. The moose prefer these for food. "We lost 16 percent of the fir trees on the western half this winter," he said. "In the last 13 years, about three-quarters of these trees have disappeared. Younger trees can't grown because the moose are eating them. While I expect the moose to increase over the summer, there are some big uncertainties ahead." The wolf-moose study is supported by Isle Royale National Park, the National Science Foundation, the Earthwatch Institute, and a number of individual donors.
Story Source: Materials provided by Michigan Technological University. Note: Content may be edited for style and length. View the Isle Royale Wolf/Moose Study Slide Show On a secluded island in Lake Superior, captive wolf packs and moose populations depend on one another for survival: The moose are the wolves' chief nutritional source, and the wolves, in turn, help keep the moose population in check. But when the wolves eat too many moose, the resulting food shortage pares down the former's number, controlling their population, as well. And for the past five decades, scientists have watched this ecological dance in an effort to better understand the predator–prey relationship. Teams of scientists from Michigan Technological University led by wildlife ecologist Rolf Peterson since 1975, and joined in 2000 by John Vucetich, assistant professor of forest resources and environmental science, have carefully monitored the waxing and waning of these animal populations. The link between hunter and hunted has revealed the species' interdependency, as well as their shared vulnerability to the isle's often-tough living conditions. The plant-eating moose must scrounge during the harsh winters to avoid starvation, living on pine needles and twigs. When food becomes too scarce and the moose populations decline, some of the wolves that rely on the moose also die out. Scientists have found that there are currently four packs of wolves roaming the isle that continually battle for turf and food—and their rise and fall, as described by the researchers, can often stem from seemingly insignificant events. For example, in January 2000 researchers watched as a lone female wolf entered the territory of one of the wolf bands they had dubbed the Middle Pack. She was attacked by the wolf pack and forced into the chilly water of Lake Superior. Though wounded, she swam back to shore and survived. A male split from the Middle Pack and came to her aid, staying with her and licking her wounds after she had been left for dead. The ostracized couple later mated, founding what became the Chippewa Harbor Pack, a group that has since conquered territory in the Middle Pack's dwindling empire. Though the scientists don't know if such individual and pack behavior is a common occurrence, observations like these on Isle Royale provide insight into how animal societies function as well as the vicissitudes of the food chain cycle on Isle Royale, also helping to inform other models of the natural world. Researchers have studied the predator–prey dynamics on Isle Royale since 1958, making the project the longest-running of its kind. The Lake Superior archipelago was declared a U.S. National Park in 1940, and this designation saved the remaining wilderness from further logging and mining. The dwindling animal populations rebounded as human industry receded, and the periodic fluctuation of wolf and moose numbers began anew, continuing to this day. The Isle Royale Wolf/Moose Study celebrates its 50th anniversary in late July. Groups such as the National Park Service and the Earthwatch Institute, among others, help fund the research led by the Michigan Tech faculty. View the Isle Royale Wolf/Moose Study Slide Show |
Why is an increase in the number of wolves usually followed by a decline in the moose population
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