A pod of sperm whales are observed sleeping vertically, floating in a state of suspended animation. The clip is from the nature series Big Blue (episode 4 of 7). Sperm whales are believed to only sleep for brief periods of 12 or so minutes.
“Many mammals show species-typical sleeping behaviour, such as dogs circling before lying down, lending support to the idea that sperm whales sleep during these drift dives,” study author Dr. Patrick Miller, a professor of biology at the University of St. Andrews in Scotland, said in a written statement.
Evidence for this study came about a few years ago when Dr. Miller and his researchers found a pod of snoozing sperm whales at sea, off the coast of Northern Chile. As the whales floated motionless, with their noses at the surface of the water, they seemed unfazed by the approaching boat of researchers.
“Reduced responsiveness that reverses with sufficient stimulation to cause waking is another important criteria that allows us to consider this to be a sleeping behavior,” Dr. Miller noted. Dr. Miller said. His research suggested that such whales are totally asleep for about 7.1 percent of their time at sea, most often between 6 p.m. and midnight.