Isle Royale’s predators and prey
(Feature photo: Yellowstone National Park gray wolf copyright 2010 Patrick McCabe)
By Karen Rodriguez
“The moose and the wolf need no one to lead them…but only a place to be left alone.” Durward L. Allen*
The story of how wolves arrived on Isle Royale is conjecture. It is thought that in the winter of 1948-1949, seven gray wolves (Canis lupis) crossed the 15-20 miles from Ontario’s Sibley Peninsula to Isle Royale on an ice bridge across Lake Superior. Nearly 70 years have passed during which the wolf population grew and then plummeted to its 2017 number of two. During that time, scientists have conducted extensive research on wolves and their primary Isle Royale prey, moose.
Part of the State of Michigan, Isle Royale is an archipelago consisting of the largest island on Lake Superior, 45 miles (72 km) in length and 9 miles (14 km) wide, surrounded by approximately 450 small islands, plus submerged lands within a 4.5 mile (7.24 km) radius. Designated a U.S. National Park in 1940, 99% a wilderness area under the Wilderness Act of 1964 by 1983, and an International Biosphere Reserve in 1980, Isle Royale adjoins the border of the Canadian Lake Superior National Marine Conservation Area.
Named Isle Royale by French explorers, Native Americans called the large island Minong, or place of blueberries. The island is forested with both boreal and deciduous trees and contains many small lakes and wetlands. The geology is post-glacial rugged with a basalt spine from one end of the island to another.
Within the basalt a vein of copper attracted Native American miners and later, European miners. In addition to copper mining, timber was cut. Fur traders trapped beaver, Canada lynx, marten, and other fur bearing mammals, and populations including caribou, Lake Sturgeon and the now extinct passenger pigeon were hunted and fished.
At the request of the Michigan state legislature, Adolph Murie surveyed Isle Royale resources in 1929 and 1930. He found vegetation deteriorating or disappearing because of over-browsing by a growing moose population. Moose had arrived, presumably in the early 1900s on an ice road from Ontario. Murie’s conclusion was that the moose population needed to be reduced or lack of vegetation would lead to starvation and disease. He also suggested that a possible solution would be to introduce a predator. As Murie predicted, the moose population plummeted. Interestingly, in the 1930s, as the moose’s predicament became bleaker due to lack of sufficient edible vegetation, the solution tried was to capture moose and ship them off of Isle Royale. Over a three-year period, 71 moose were captured and shipped to the Upper Peninsula of Michigan where moose had been nearly extirpated. They failed to prosper and were sometimes illegally shot.
In 1936, a fire burned more than a quarter of the island. Subsequent years showed a growth of vegetation, brush and early tree species, in the burned area. The burned area became a major feeding area for moose. The moose population recovered. The population was soon exceeding carrying capacity. The question in 1940 was what to do in the absence of natural predators. Consideration was given to establishing a hunting season as a control.
But then the wolves arrived. In addition to moose, red fox, snowshoe hare, mink, weasel, red squirrel, deer mice and several bat species comprised the mammals that were present. Caribou, Canada lynx, marten, and coyotes had been extirpated from the island. There were no deer or bear on Isle Royale (still true today).
In addition to the wolves that arrived independently, four human-raised wolves from the Detroit Zoo were introduced to Isle Royale in 1952 by a Detroit newspaperman and Lee Smits, a wolf advocate, with permission from the National Park. The wolves did not fare well because they were too human-dependent. Two were soon shot, one was captured and removed, and one was not seen again but may have lived several years on the island.
The scientists who would spend the next decades studying the island and its inhabitants arrived in the early 1950s. Isle Royale was the perfect research laboratory. Isolated, remote and publically owned, the island’s wild wolf and moose populations reflected a predator-prey relationship that could be observed, monitored and studied with few outside influences.
When Durward L. Allen of the U.S. Fish and Wildlife Service heard wolves had been spotted on Isle Royale he unsuccessfully requested a budget to study them. By 1954 he had moved to a position at Purdue University in the Forestry and Conservation department where he secured funding to direct the first of many subsequent Isle Royale studies. From 1959-1961, graduate student L. David Mech with others, observed and documented the hunting and social behavior of the wolves. They also observed moose, beaver, snowshoe hare and fox. Later, in 1988, researcher Rolf Peterson began to live trap and radio collar wolves to better keep track of their movements. Under Peterson’s guidance one of the longest running predatory-prey studies anywhere continues today.
In the spring researchers collect bones of wolves and moose that perished over the winter; moose antlers are also collected. In the winter researchers fly over the entirety of Isle Royale for a yearly count of both species. Remote sensing is used to monitor moose population size and movement. Wolf kills are observed and photographed. Autopsies are conducted. DNA samples are studied.
Maligned as ruthless killers, wolves have been poisoned and hunted throughout human history. But the scientific studies conducted on Isle Royale over the past 70 years tell a complex story about a shy predator. Research findings are many and include: wolf food is primarily moose supplemented by beaver and snowshoe hare; the wolves, in a pack or alone, judge whether to kill a moose or leave it alone by first testing it; old moose, calves and sick adults are the primary prey; a moose that looks healthy to a researcher may actually be infested with the winter tick or a disease and therefore judged edible by a wolf; wolves howl when they are “happy” or playful; and, population health cannot be determined by observations over a couple of years—decades of study are required to determine population trends.
Even on this isolated island humans are having an impact on the wolves and moose. In 1981, a Chicago visitor illegally brought a dog infected with canine parvovirus to the island. The wolf population crashed—the population fell from 50 to 14. Studies of Isle Royale wolf teeth collected since the early 20th century show that global actions and conditions are impacting the island:
“In the island’s wilderness, which is as pristine as any in the continental United States, wolves have inadvertently recorded the two largest atmospheric perturbations generated by modern humans—the radioactive fallout from thermonuclear weapons and the accelerating rise in CO2 from the combustion of fossil fuels. For any thinking human, this should underscore the scale of the modern human enterprise, and should hint at the magnitude of the challenge of maintaining natural processes in our national parks. There is no place on the planet that remains unaffected by human technology, and the most insidious of all environmental risks are those we cannot see.”**
In 2016 a new threshold was crossed in the Isle Royale predator-prey story. The wolf population, genetically isolated, shrank to two individuals; the moose population increased to more than 1,300. Without intervention, the National Park stated, “It is likely that the moose population on the island will continue to increase until a lack of available forage, disease, weather, or other population control measures cause a decline.”*** Furthermore, “At this time, due to the low number remaining, genetic inbreeding, and the remoteness of Isle Royale, natural recovery of the [wolf] population is unlikely due to tenuous nature of ice bridge formation.”****
The Park released a preliminary Environmental Impact Statement late in 2016: “The purpose of this draft plan/EIS is to determine whether and how to bring wolves to Isle Royale to function as the apex predator in the near term within a changing and dynamic island ecosystem.”***** The draft plan includes four options: A. No Action (wolves would not be reintroduced to the Park); B. Immediate Limited Introduction (wolves would be introduced over a three-year period); C. Immediate Introduction with Potential Supplemental Introductions (could introduce more wolves over a 20-year period); and D. No Immediate Action, with Allowance for Future Action (monitoring of current situation with ability to reintroduce wolves at a future date). Option B, Immediate Limited Introduction is the option preferred by the National Park. In any of alternatives B, C or D, wolves would be captured from nearby Great Lakes locations if they appear suitable for the Isle Royale environment. The National Park is analyzing the more than 5,000 comments received before a decision is made.
Reintroducing species to National Parks is not an unknown practice. In 1995, 70 years after they were eradicated in Yellowstone National Park, wolves from Canada’s Jasper National Park were successfully reintroduced. Since then the wolves have checked the growth of the elk population thereby protecting the valleys from overgrazing. Likewise, Isle Royale wolves would check the moose population and protect forest and wetland community vegetation from heavy moose browsing. A final Isle Royale decision on whether to introduce wolves from the mainland has not been announced; however, a decision is expected by the end of 2017.
Postscript October 1, 2018: Two wolves were released onto Isle Royale today.
Patrick McCabe: The photos of the Yellowstone wolves were taken in February 2010. One morning we spotted a bloody corpse along the bank of the Madison River and stopped to investigate. We stood around for about 45-minutes and did not see any activity. During this time a group of about 20 snowmobiles stopped to see what we were looking at and then they continued on. Shortly after they left we spotted a wolf coming out of the woods and tentatively making its way to the corpse with several starts and stops. Our thought was this was a female who might not have gotten a lot of food the night before when a larger pack was feeding. After some time the larger dark wolf appeared. This wolf never fed on the corpse while we were watching. We watched the gray colored wolf feed for about 30 minutes before it went back into the woods. The wolves could clearly see us and we could see them. I think both sides knew the Madison River was between us so we were all safe!
*Allen, Durward L. Wolves of Minong, Their Vital Role in a Wild Community. p. 414-415.
**Peterson, Rolf O. The Wolves of Isle Royale, A Broken Balance. p. 57.
*** National Park Service, Department of the Interior. Isle Royale National Park, Draft Environmental Impact Statement to Address the Presence of Wolves. p. 6, ****7, *****iii.
Allen, Durward L. Wolves of Minong, Their Vital Role in a Wild Community. Boston, MA: Houghton Mifflin Co. 1979. (Also published as Wolves of Minong, Isle Royale’s Wild Community by the University of Michigan Press in 1993.) Allen is a storyteller who documents the years of research, winter and summer, on his beloved Isle Royale.
Mech, L. David, PhD. The Wolves of Isle Royale. Washington D.C.: United States Government Printing Office. 1966. (Fauna of the National Parks of the United States, Fauna Series 7) Mech’s technical thesis is the first comprehensive study on the predator-prey relationship of Isle Royale wolves and moose.
Peterson, Rolf O. The Wolves of Isle Royale, A Broken Balance. Ann Arbor, MI: University of Michigan Press. 2007. Peterson follows his mentor Allen as a storyteller. This book is passionate and thoughtful and a prediction of the demise of the wolf population as well as a philosophical discussion of possible actions to address the demise.
Isle Royale National Park is open for backpacking, hiking, canoeing, and kayaking from April through October. Surrounded by Lake Superior, the Park is accessible by seaplane, private boat, and commercial boats from Grand Portage, MN and Copper Harbor or Houghton, MI. A hotel, cottages, restaurant, showers, laundry and a store are available at the marina in Rock Harbor on the eastern end of the island; cabins, showers, laundry and a store are at Windigo on the western end.
For further reading:
Mlot, Christine. Two wolves survive in world’s longest running predator-prey study. Science. April 18, 2017. A brief article on the status of the draft Environment Impact Statement regarding reintroduction of wolves to Isle Royale is up-to-date information as of mid-2017. (http://www.sciencemag.org/news/2017/04/two-wolves-survive-world-s-longest-running-predator-prey-study)
National Park Service, Department of the Interior. Isle Royale National Park, Draft Environmental Impact Statement to Address the Presence of Wolves. December 2016. This is the draft Environmental Impact Statement in its entirety. A decision on the fate of Isle Royale wolf reintroduction is imminent in 2017. (https://www.nps.gov/isro/getinvolved/wolf-eis.htm)
Content and photos copyright 2017 Karen Rodriguez except: Yellowstone wolf photos copyright 2010 Patrick McCabe. For more Patrick McCabe photos see: psmphotography.com