A full-grown moose has few natural enemies. Siberian tigers prey on adult moose. Wolves also pose a threat, especially to females with calves. Brown bears are known to prey on moose, although bears are more likely to take over a wolf kill or to take young moose than to hunt adult moose on their own. American black bears and cougars can take moose calves and can sometimes kill adult cows. Wolverine are most likely to eat moose as carrion but have killed moose, including adults, when the moose are weakened by harsh winter conditions. Killer whales are the moose's only known marine predator. They have been known to prey on moose swimming between islands off North America's northwest coast.