Whales sleep with half a brain at a time

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Washington, January 30 : Researchers at the University of St. Andrews Gatty Marine Research Institute have found that sperm whales perform slow, rhythmic dives while asleep, a finding that suggests that the seafaring mammals perhaps sleep with one side of their brain at a time.

The researchers believe that the two sides of a whale's brain keep on alternating until both are rested.

They also believe that sperm whales may break a world record for least amount of sleep needed by a mammal.

"If the only sleep sperm whales get is during these drift dives, it would be less than any mammal studied so far," Discovery News quoted Patrick Miller as saying.

For their study, Miller and his colleagues affixed suction cups with data-logging tags onto 59 sperm whales at various open-water locations worldwide. With the help of the tags, the researchers could monitor the movements anytime.

The study showed that the whales performed the mesmerizing drift dives 7.1 percent of the time, usually between 6 p.m. and midnight.

The researchers reported noticing two types of drift dives-head-up drift dives that happened when a whale's rear end slowly sank into the water from a horizontal posture, and head-down drift dives that occurred as the whale descended slowly with its head directed towards the ocean floor.

During the second type of drift dives, the whale travelled downward about one or two body lengths in depth before flipping back upward toward the water's surface.

The researchers believe that the whale's internal buoyancy causes this natural upward motion.

"Because the drift dives are quite short (averaging around 12.7 minutes in duration) and are broken by the need for the whale to move to the surface to breathe, it seems that they sleep over short interrupted periods," said Miller.

"Cat naps for sperm whales, perhaps?" he added.

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