Why Black Bears Sleep in Trees

The ancestors of modern North American bears evolved in Asia during the Pleistocene, wandering over to Alaska during several appearances of the Bering land bridge, between the Bering and Kamchatka Peninsulas. Advancing and receding glaciers, fueled by evaporating sea water, caused ocean levels to alternately drop and rise, exposing and resubmerging the Bering Strait. The ancestors of black bears came across half a million years ago, and it is suspected that black bears adapted to climbing trees to escape the larger, faster and more strictly carnivorous short-faced bear, which, fortunately for us, joined the extinction parade about 5,000 years ago. The glacially isolated polar bears split off from grizzlies in Asia about 130,000 years ago, and followed grizzlies across the land bridge about 100,000 years ago. Grizzlies stayed bottled up in Alaska for a while, possibly thanks to the presence of the same short-faced bear in the areas that became Canada and the U.S.

These factors set the pattern for survival for each species: black bears tend to retreat, often up trees, while the heavier, stockier grizzly, evolving in the more open tundra and taiga, areas with fewer and smaller trees, developed the best-defense-is-a-great-offense approach to survival.


It's an evolutionary adaptation to survive short-faced bears and sabertooth tigers.

Folksonomies: evolution black bears

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 Bears and People
Electronic/World Wide Web>Internet Article:  Steve, Hall and Wendy, Hall (2014), Bears and People, Adirondack Wildlife, Retrieved on 2014-04-21
  • Source Material [www.adirondackwildlife.org]
  • Folksonomies: bears