BRETT FRENCH

Bison seem pretty social, so friendly that some Yellowstone National Park tourists wrongly think they can pet the "fluffy cows," sometimes resulting in serious injury to the petter.

Although weighing up to 2,000 pounds, bison appear rather docile as they hang out in small groups, the exception being the old, ornery bachelor bulls. Each August the animals gather in large numbers in places like Yellowstone's Hayden Valley for the annual breeding season, called the rut.

Throughout the year they also congregate in random groups, hang out together for a while for some unknown reason, then scatter. Scientists refer to this behavior as fission-fusion social organization. Other animals demonstrating similar behavior include zebras, reindeer and pronghorns.

Montana State study

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