Grizzly bears are a subspecies of brown bear, set apart by their size, their silver-tipped fur and their trademark hump of upper-back muscles. Scientists think North American grizzlies (Ursus arctos horribilis) evolved from Asia's Ussuri brown bears, which migrated into Alaska from Siberia some 100,000 years ago. They eventually spread as far as Mexico and the Great Lakes, but European settlers and U.S. pioneers later wiped them out across most of the Lower 48 states, leaving only a few pockets in Idaho, Montana, Wyoming and Washington. All U.S. grizzlies were added to the endangered species list in 1975 except those in Alaska, where they're still abundant.
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Like most bears, grizzlies are omnivores. Nuts, berries and salmon are some of their favorite foods, but they'll eat almost anything — including trash. Packs of them used to gather at open-pit dumps in Yellowstone National Park during the early 20th century, drawing crowds of tourists and eventually becoming reliant on trash for food. Realizing the bears needed a natural food source, officials began closing the dumps in the late 1960s, triggering a crash in the park's grizzly population. But thanks to three decades of federal protection, as well as reduced logging in the area, the grizzlies of Yellowstone have now clawed back up to about 600 bears.
Grizzly-human encounters have also risen in recent years, but they're fatal to bears far more often than to people, and are still less common than they used to be. Yellowstone had an average of 48 annual grizzly attacks from the 1930s to the '60s, but today there are only about five per year, even though park visitation has tripled during the same period. Still, the effects of global warming — namely the loss of dietary staples like whitebark pinecones and cutthroat trout — are expected to push grizzlies closer and closer to towns and cities, further testing their rocky relationship with people.
Yet climate change isn't all bad news for grizzlies. Warmer weather is expanding their range northward, helping them flee humans by pushing deeper into Canada and Alaska. That's likely just a short-term perk, however, and it may also doom one of grizzlies' closest relatives, polar bears, which are already in trouble as climate change hinders their seal-hunting abilities. Polar bears are now trying to eat more plants instead, but since they've adapted to feed on blubber, not fiber, biologists worry the more omnivorous grizzlies will take over their habitat. There is still one silver lining for polar bears, though: Scientists in Canada recently reported the first evidence of a wild polar-grizzly bear hybrid (aka "grolar" or "pizzly"), suggesting the two predators might be able to get along after all.
• Philosophical Transactions of the Royal Society B: "Hybridization, ecological races and the nature of species" (2008)
(Text by Russell McLendon)
(Photo: Alaskan Dude/Flickr)