The wolf known as 016M was released on Isle Royale in March 2019 after being transported from Ontario. Image: National Park Service
By Eric Freeman
For the first time, scientists have documented an adult wolf killing red fox cubs in their den.
The event occurred in Isle Royale National Park, where researchers found evidence that an adult male wolf known as 016M attacked the kits, possibly killing and feeding on at least two of them – and possibly also killing a third littermate.
According to a study recently published in the journal “Northeastern Naturalist”, the kittens had dens in the hollow trunk of a northern white cedar.
The attacker was captured by helicopter in Wawa, Ont., in March 2019 and moved to Isle Royale as part of a National Park Service program to rebuild the island’s near-extinct wolf population, which had fallen to just two adults.
The wolf was given ear tags and fitted with a GPS collar before being released near Windigo on the southwestern tip of the island.
The attack happened about two months later, according to the study.
Red foxes have lived on Isle Royale in Lake Superior since 1925. Wolves first arrived there in the late 1940s.
Scientists from Isle Royale National Park, the State University of New York’s Global Wildlife Conservation Center, the US Geological Survey and the Ontario Ministry of Natural Resources and Forestry carried out the research.
Wolves and foxes don’t usually compete for prey, according to wildlife biologist Mark Romanski, manager of the national park’s natural resources program and co-author of the study.
Wolves are the main predators on Isle Royale and generally do not kill foxes, especially when food for both species is plentiful, according to the study.
Wolves on Isle Royale feed mainly on moose and beaver. The diet of red foxes includes small mammals, fruits and birds, although they feed on carcasses killed by wolves.
“Food scarcity for wolves after translocation seems unlikely, given that American moose and beaver densities were at or near the highest recorded,” the study said.
No one knows the real reason for the rare attack.
“This wolf spent six days at the den site and invested a significant amount of energy in digging the den and killing the kittens,” they wrote.
As to why he did so, scientists have theorized that his recent translocation, his unique non-pack status, his limited knowledge of local food resources, and the risk of injury from attacking adult moose could have created “food pseudo-limitation effects”. .”
Researchers found the site of the attack using the wolf’s GPS tracker.
They discovered evidence that the wolf had attacked the two partially eaten carcasses.
The intact carcass of the third kit had multiple puncture wounds in its abdomen that were “consistent with a large carnivore” but could not be definitively attributed to the wolf, they said.
The study indicates that the wolf may have partially consumed two of the kits and the scavengers may have eaten more of the carcasses.
Since most red fox litters have three to six kits, the wolf may have eaten others, he said, although adults sometimes split their litters between two dens.
American martens, crows and pine marten prey on red fox kits, but these species would not have been able to dig down the hollowed tree trunk to reach the den or create the large puncture wounds found on the carcasses, according to the study.
Nineteen wolves, including 016M, were transplanted to the island from Ontario and Minnesota between September 2018 and September 2019. Isle Royale’s wolf population has since increased to their twenties, not counting those born this spring, Romanski said.
The ultimate goal of GPS tracking and related research is to “understand the ecosystem services” that wolves – those transplanted and their offspring – perform on Isle Royale, he said.
Documenting these rare kills helps scientists understand the effects when a dominant competitor is reintroduced into an ecosystem, according to the study.
“We were hoping they would kill the moose,” he said, referring to the moose bloom that had devastated plant life on Isle Royale as wolf numbers plummeted.
And, as hoped, they managed to kill moose and beaver, he said.
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