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    Some humans prefer sleeping on their sides, while others sleep on their backs or their stomachs. Sperm whales? They've got their sleeping positions down straight. According to researchers at the University of St. Andrews studying the giant marine mammals' resting behavior, wild sperm whales "drift" off to sleep vertically.

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    DREAM DANCERS 

    The new study released by Dr. Patrick Miller of the University of St. Andrews captured video of sperm whales sleeping for short periods of time while performing rhythmic dives. 

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    SLEEP DIVING 

    Miller likens their sleeping patterns to those of many other mammals. "Many mammals show species-typical sleeping behavior, such as dogs circling before lying down, lending support to the idea that sperm whales sleep during these drift dives." 

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    EYES WIDE SHUT 

    Researchers not only found that these large-toothed whales sleep similarly to terrestrial mammals, but also sleep with both their eyes closed. 

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    NO SLEEP IN THE WILD

    Additionally, scientists found that wild sperm whales sleep differently than those in captivity. Wild sperm whales sleep 7.1-percent of the time, indicating that they sleep less than any mammal, and much less than their captive siblings. 

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    SLEEP DISCOVERY 

    Dr. Miller's research concerning sperm-whale sleeping patterns does not stop here. "The challenge for the future is to develop new technologies that might allow us to measure the brain waves of these animals during sleep at sea," he said.