I know that an elephant or a rhino could likely kill a grizzly bear easily. I’m thinking of the native North American fauna – does any other species pose a threat to these great bruins?
Polar bear
Another grizzly bear
Various microbes
Humans …
An angry bull moose could do some serious damage. Even an elk could cause a fatal injury. I can’t say I have heard of this happening but they do have the power and weapons to kill a grizzly if they had a little luck on thier side.
A pack of wolves. I do not know how well a bear would hold up to snake venom.
Bison or Muskox might have a chance by goring a grizzly. An elephant seal could take one out because it’s so much larger. Aside from humans I think the Grizzly’s biggest fear is a bigger bear.
A poisonous snake? Some other deadly venomous creature?
Toxoplasma Gondii, the protozoa that casus toxoplasmosis, which grizzlies can get, and which can be fatal.
Or a brontosaurus. I’ll bet a brontosaurus could kill a grizzly.
OP didn’t specify “full-grown”, so I think it opens up some more possibilities…
Oh, and a wolverine.
Should one take a dip in the ocean, an Orca or Great White Shark.
With a great deal of luck, a Mountain Goat might be able to fatally gore one if it got in under the bear’s guard. They have occasionally killed humans.
White-tailed and Mule Deer could also conceivably cause fatal injuries, although it would have to be a very lucky deer and very unlucky grizzly.
Rabbits. Or one Rabbit.
Wolves, if sufficiently motivated by hunger and in a large enough pack, but probably not without casualties. Otherwise, excluding humans, grizzly bears are at the top of their food chain in their normal habitat. Potential opponents listed here would need to rely on luck.
Not North American fauna per se but along a similar latitude, it’s reported that Siberian Tigers will kill Russian brown bears, although they will selectively go after just juveniles and females and won’t approach a full grown boar.
A chicken, if the grizzly choked on a bone.
Yeah, I have heard about that.
Hmmm. This does make me wonder how well a lion would do against a grizzly…
I started to bring this one up. An 800# tiger against an 800# grizzly would be a good fight. A tiger lacks the will to fight as much as an angry bear. But defensively he would do some real serious and possibly fatal damage to the bear. A 500# tiger against an 800# bear my money would go on the bear.
Snakes and bears live in different ecosystems.
A most foul, cruel, and bad tempered rodent!
A hippo would also kill a grizzly. they look ponderous and slow, they are not, and they have an evil attitude.