Adult killer whales in captivity sleep between five and eight hours a day, floating on the bottom of their pool or near the water's surface, with periodic breaks for air. But when Jerome Siegel of the University of California at Los Angeles and his colleagues studied two adult female whales and their calves at SeaWorld San Diego, they discovered that the new moms gave up shut-eye completely as they cared for their offspring, who swam continuously and surfaced for air every three to 30 seconds. After about a month, the calves began to introduce periods of rest into their routines, and they and their mothers slowly approached a sleeping pattern similar to that seen in other adult cetaceans. Observations of four dolphins and their calves housed in Russia produced similar findings, the team reports in the current issue of the journal Nature.
Although all other mammals that have been studied sleep the most right after birth, being constantly on the move could have some benefits for the cetaceans, the team writes. For example, the activity would reduce the risk of predation and help maintain body temperatures while their weight increases and their blubber develops. According to Siegel, the mammals have somehow found a way to manage sleep deprivation and use it to facilitate, rather than hinder, a crucial phase of development for their offspring. "Their bodies have found a way to cope," he says, "offering evidence that sleep isn't necessary for development and raising the question of whether humans and other mammals have untapped physiological potential for coping without sleep."