Wolves and Moose on Isle Royale

 

People often assume that nature, if left to her own devices, is stable and unchanging. They believe that change is caused by human tinkering or interference, and it’s always bad.

But this is not the case.

While humans can and do change their environment, they are not the only causes of change. Some happen naturally. A good example of this has occurred on Isle Royale, an island in Lake Superior which is now part of the National Park system.

Isle Royale is now famous for its wolf and moose populations. Because it is quite isolated and only has one dominant predator and one dominant prey, it is the ideal place to study the relationship between the two species. Durward Allen initiated the Isle Royale Wolf-Moose project in 1958. The study is still going on.

But neither wolves nor moose have been on the island for long, and it is likely that neither are there because of human tinkering or interference.

In the early twentieth century, the largest mammals on Isle Royale were the Canadian lynx and the boreal woodland caribou, a subspecies of reindeer found primarily in Canada with small populations in the United States. Archeological evidence indicates both of these species had inhabited Isle Royale for 3,500 years. Their demise on the island can be attributable to human actions such as hunting and trapping and loss of habitat through mining, logging, and fires. But it is likely that the arrival of competitors also caused the lynx and caribou population to dwindle to nothing. Those competitors arrived on the island not by human intervention, but by their own initiative. 

It turns out that Isle Royale is not as remote as it would seem. At least, not throughout the year. The 14 miles between the Minnesota shoreline and the island may be impossible to swim for most species, but it can be easily traveled when the water freezes over. Lake Superior last froze over completely in 1996. In 2014 and 2019, ice covered over 90% of the lake’s surface. Ice bridges, narrow pathways of ice that can reach from the mainland to the islands, are more common.

Ice bridges are probably how coyotes managed to appear on the island around 1905. Often called brush wolves in the diaries and accounts of Isle Royale Islanders, these canine predators ate snowshoe hares, squirrels, and other small mammals. This put them in direct competition with the Canadian lynx, whose numbers declined until it was believed to be completely gone from the island by the 1930s. However, there have been occasional sitings of lynx, the most recent being in 1980. Whether there was a small resident population of reclusive lynx or the cats crossed back and forth over ice bridges is up for debate.

Moose first arrived on Isle Royale soon after coyotes, with 1909 being the most likely year. There are several theories about how the big mammal came. Some suggest that they were stocked on the island for the purpose of recreational hunting. This seems unlikely. If someone had managed to capture and cage several moose, then transport them to the island, they would have left some sort of documentation; managing such a feat with so large and bad tempered an animal demands serious bragging rights. Other sources suggest that moose swam across Lake Superior from Minnesota,

and while a long distance, moose are strong swimmers and this could be possible. It is more likely that moose used an ice bridge to reach Isle Royale, just as the coyote had. Moose and caribou competed for the tender shoots and buds of willow, aspen, and birch until deciduous trees were largely eradicated. The last boreal woodland caribou on Isle Royale was documented in 1925. Now, moose rely on balsam fir and, when other food sources are overgrazed, lichen. For fifty years, their numbers fluctuated in a boom-and-bust cycle, rising when weather conditions were good and food abundant and declining in years of scarcity and harsh weather. And then wolves came.

In 1949, during a particularly harsh winter, wolves crossed an ice bridge from Ontario to the island. No one is sure just how many wolves arrived, but it could have been a single pair. Wolves flourished on the large moose herds, outcompeting the coyotes, who disappeared within a few years.

Without much (or any) human intervention, three species: the lynx, the caribou, and the coyote had left the island and the moose and wolf had taken their place.

In 1958, when Durward Allen initiated the Isle Royale Wolf-Moose project, he and other ecologists expected to document a “balance of nature” in which the wolf and moose populations became relatively steady in relation to each other. They believed that when moose herds increased, wolf populations would also. What actually happened was much more complicated. The moose population has ranged from as low as 500 to as high as 2500. The biggest drop in population came in 1996, when the most severe winter on record and an unexpected outbreak of moose ticks caused the population to collapse. It seems disease can affect moose populations as much as predation from wolves.

Wolf populations have been erratic as well, ranging as high as 50 to an unsustainable two. In 1980 the wolf population crashed after humans inadvertently brought the disease canine-parvovirus to the island.  By the late 1990s, it was clear that the small number of wolves that had begun the island’s packs had led to inbreeding, which was weakening the individuals. In 1997, a single male wolf crossed from Ontario on an ice bridge, reinvigorating the gene pool. It appears that in 2008 two wolves left the island the same way.

By 2017, when there were only two wolves left of the island, authorities decided to step in and help nature restore her balance. After some debate as to whether the introduction was an unnatural intervention, four wolves were brought from Minnesota in 2018.  The next year, another 15 wolves were released at Isle Royale in hopes of bringing stability to the ecosystem.

As of early 2024, the wolf population on Isle Royale is estimated to be around 30 wolves, which represents a stabilized population in four distinct wolf packs. Now, Park Service wildlife biologists are talking about bringing back the lynx.

My historical novel, Perspective, is set in the 1930s, so the moose was on the island, but the largest predator was still the coyote. It tells the story of Genevieve Williams, an artistic 12 year old girl who is put on a ferry to Isle Royale to live with a father she's never met. Genevieve has one terrifying encounter with a moose early on in the story, but learns to love the ungainly animals and the wild beauty of the islands. When the government decides to create a national park on the island, Genevieve tries to come up with a plan that will allow her and her father to stay. The novel, written for middle grade readers and up, will be published in early october and is presently available for pre-order.