Grizzly and American black bears may be cousins, technically, but that certainly doesn’t take the whole bear-eats-bear scenario off the table.
Last month, Susan Griffith posted footage to Facebook which she described as “one of the craziest things we have seen on a drive home” in east-central British Columbia: a grizzly roughly handling the carcass of a black bear right along a road.
The grizz looks as if it’s attempting to drag the dead bear up the fairly steep roadside slope.
It’s not clear whether the grizzly killed the black bear, or was simply taking advantage of a scavenging opportunity – perhaps the black bear had been struck by a car. As is the case for for many other critters, collisions with vehicles can be a significant source of mortality for bears – the leading cause, in fact, for some populations of black bears, which exhibit signs of heightened stress when crossing high-traffic roads. And that’s a worldwide ursine problem: Earlier this year, for instance, Italians mourned a well-known and regularly seen Apennine brown bear nicknamed Juan Carlito after he was killed by a car.
Whether or not this was a predation event, grizzlies – a North American subspecies of the Holarctic brown bear – are known to occasionally prey on black bears. Though relying heavily on plant and invertebrate foods, both bears are opportunistic predators, and grizzlies in particular can become quite adept at preying on larger mammals, such as adult elk and moose. While there’s plenty of size variation across the continent, grizzlies tend to significantly outweigh black bears, giving them a size advantage. And the grizzly, which came of evolutionary age in open, exposed Pleistocene landscapes, is generally fiercer than the black bear, a forest-adapted species that often retreats up tree trunks when threatened.
Speaking about the B.C. video to Hannah Osborne for Live Science, U.S. Geological Survey biologist Frank T. van Manen, leader of the Interagency Grizzly Bear Study Team, said grizzly predation on black bears had been documented multiple times in the Greater Yellowstone Ecosystem. Among these were a “male grizzly that pulled a black bear out of a den (i.e., this occurred in late fall), completely consumed it over the course of days, and repeated the same pattern with another denned black bear about a week or two later.”
He further noted to Live Science that, given this is the time of year when bears are in the intensive, pre-winter packing-on-the-pounds mode known as hyperphagia, a seasonally fattened-up black bear – already dead or not – represents quite the boon of a meal for a grizzly.
However common or not grizzly predation on black bears is, it’s certainly rarely seen by people – but it has happened before. In October 2018, for example, hunters in Alberta, Canada filmed a large grizzly digging into a den occupied by a sow black bear and her two cubs; the grizzly killed one cub, whose mother and sibling escaped. (More sensitive viewers best stay away from this footage):
And in 2013, hikers in Banff National Park in the same Canadian province came across a big male grizzly – one known as no. 122 to researchers, who considered him the “the largest, most dominant grizzly bear on the landscape” – feeding on a black-bear carcass officials reckoned was likely a predatory kill.
Lest you start worrying too much about the well-being of American black bears in grizzly country, bear in mind (apologies) that they’ve coexisted for tens of thousands of years, and that black bears are skilled at steering clear of their bigger brethren. Especially where they share the landscape with grizzlies, black bears stick closer to forests, where their superior tree-climbing ability gives them plenty of go-to escape habitat. (Hump-shouldered and long-clawed as they are, full-grown grizzlies are mediocre tree-climbers at best.)
And research indicates black bears may be more frequently active during the day, perhaps to avoid the more dawn/dusk-active (crepuscular) and nocturnal grizzly. (In shared landscapes, mainly diurnal black bears and mainly crepuscular female grizzlies may both be timing their activities to limit run-ins with predominantly night-roaming male grizzlies, threatening to black bears and grizzly cubs alike.) A study in northeastern China similarly suggested the diurnality of Asiatic black bears there may be due to the afterhours schedule of resident Ussuri brown bears.