Beaver-hunting wolves have perfected a sit-and-wait strategy

We think of wolves as pack hunters. They're fast and indefatigable, capable of chasing down and cornering fleet-footed prey like moose and deer. 

But they don't always hunt in packs, and they don't just go for fast food. They also have a taste for slower, but more elusive fare — like the beaver.

Beavers are careful to not travel far from the safety of their ponds, but from time to time they leave the water to take down trees to repair their dams and lodges.

And new research suggests it's in that moment of vulnerability that the wolf, sometimes having quietly waited in place for a day or more, is ready to pounce.

"What it really reveals to me is just that these critters are unbelievably smart," Sean Johnson-Bice, a PhD student at the University of Manitoba told Quirks and Quarks.

Johnson-Bice is co-author of a research paper in the journal Behavioural Ecology that explores how wolves adapt their strategy, from speed and endurance to patience and guile, to ambush unsuspecting beavers.

He said they found wolves would lie in wait for beavers between about eight to 12 hours at a time, on average.  But in extreme cases they'd patiently hide for up to 30 hours. In picking a hiding place, they appeared to account for wind direction to avoid detection.

All this challenges the conventional view of wolf hunting habits, said Johnson-Bice.

Like many large apex predators, wolves are traditionally regarded as cursorial hunters, meaning they tend to be able to outrun and outlast prey.

But Johnson-Bice's study in Voyageur National Park in Minnesota showed wolves there, and likely elsewhere, rely on more than one hunting method.

Johnson-Bice and his team with the Voyageurs Wolf Project found in the winter, wolves mostly hunt big game: deer, elk, and moose. When the snow melts in late spring, those animals are more nimble and able to evade predation.  That's when the wolves turn their focus to beavers.

Evidence from scat and remains revealed that at that time of the year, beavers were a significant food resource for wolves.

Wolves again shift hunting approaches around June and July, targeting young and weak deer fawns, for example. They eat blueberries or go fishing in the dark. And in July and August, when the deer fawns are strong enough to dodge wolves, wolves go back to beavers. 

The wolves in the study had been outfitted with GPS collars. Clusters of points corresponding to wolf locations in the summer invariably showed they were spending a lot of time near beaver habitats.

Just like humans can pick up on features in the landscape — like a number of tree stumps filed to a fine point by beavers who chewed down trees — wolves can home in on signs of beaver activity. 

From there, the researchers say, wolves determine where the beaver spends time in vulnerable locations on land, often near a lodge or dam site or a favoured tree stand. Beavers can't see well out of water, and the locations the wolves were using to hide suggest they were aware of this, said Johnson-Bice.

Wolves also appeared to account for environmental factors when selecting an ambush spot — specifically wind direction. About 90 per cent of the ambush attempt locations were downwind of where the beaver activity was, suggesting the wolves were aware they have a scent that can be detected when upwind of a beaver.

For the most part, Johnson-Bice and his team haven't managed to catch wolves in the act of ambush. They mostly made these inferences indirectly through a combination of the GPS location hotspots in relation to beaver territory, wolf scat with beaver remains and other clues.

Still, Johnson-Bice is confident the team has documented something for the first time that could have broader implications.

"Wolves are probably the best-studied large predator in the world, and the fact that we have discovered in this study what is really a remarkably different hunting mode than what is traditionally thought is just really … fascinating," he said.

"I think that leaves open the door of, 'Do we know about if there is a flexibility with some of these other large predators?'"

Written and produced by Bryce Hoye.