Plains Bison Flehmen.

Male bison, called 'bulls' tend to become solitary with age. As the rutting season winds up, the bulls check for estrous females, displaying the flehmen behaviour. Flehmen involves curling the upper lip back and extending the neck - lasting just a few seconds, it is believed to enhance the sense of smell. Cows remain in heat for only 24 hours, so bulls need to be ready and waiting to get their chance to mate. Bull Bison flehmen, Custer State Park, South Dakota.

Bison bison

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