Orca-whale and dolphin mothers and their newborns appear not to sleep for a month after the pups’ birth, researchers report. Neither parent nor offspring shows any ill effects from the long waking stint, and the animals don’t later compensate with extra sleep.
No previously studied mammal stays awake for so long, says Jerry Siegel of the University of California, Los Angeles (UCLA), an investigator in the study.
In the months following their wakeful period, baby whales and dolphins—and their mothers—ramped up slowly to sleep amounts typical of normal adults, Siegel and his colleagues report. The infants’ sleep pattern contrasts with that of other mammals, which need extra sleep during infancy and gradually sleep less as they age.
Oleg Lyamin, also of UCLA, started observing an orca mother and her baby just after it was born at SeaWorld, San Diego. Orcas usually snooze for 5 to 8 hours a night, closing both eyes and floating motionlessly.
The SeaWorld orca mother and baby, Lyamin found, neither shut their eyes nor remained motionless. Instead, the animals were constantly active, with the infant surfacing for a breath every 30 seconds. The researchers made similar observations of another SeaWorld orca mom and baby.
The team also watched dolphins at the Utrish Dolphinarium in Moscow. Dolphins sleep with one-half of the brain at a time, closing one eye while floating or swimming about. The team observed no sleeping behavior in the first month after birth among four dolphin mom-baby pairs.
The findings, reported in the June 30 Nature, challenge prevailing notions of the purpose of sleep, some researchers say. “We’re under the belief that if you don’t get sleep, you can’t perform, and you’re at risk for developing all sorts of disorders,” says Paul Shaw of Washington University in St. Louis. For instance, rats die after being deprived of sleep for just 2 weeks.
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The UCLA data are “the beginning of a change in the way we view sleep,” says Shaw.
Scientists have commonly hypothesized that people and other animals require sleep for brain development and learning (SN: 6/1/02, p. 341: Snooze Power: Midday nap may awaken learning potential). “Here we have a developing [whale or dolphin] youngster with no evidence of sleep,” says Irene Tobler of ETH-Zurich in Switzerland. “It will revolutionize many people’s ways of thinking.”
Siegel argues that sleep is not required for brain development in these and other young animals and instead plays some role as yet unknown.
Alternatively, whales and dolphins may have evolved unusual compensatory mechanisms that permit them to develop without sleep, while other animals still require sleep for brain development, Tobler says.
Robert Stickgold of Harvard University suggests that mother and baby whales and dolphins may have evolved an unusual form of sleeping. “A sleepwalker makes it down the stairs, into the kitchen, into the refrigerator quite well while a [brain wave] recording says they’re in deep sleep,” he notes.
Stickgold says that such recordings from the animals could help determine whether the orcas and dolphins are awake.
Siegel speculates that mothers and babies of both species need constant activity to survive. The mother pushes the baby to the surface to breathe at regular intervals. Also, the baby must stay warm in cold water while it develops its blubber coat.
“The mystery is that they’re … dispensing with sleep behavior when so many sleep researchers have assumed that sleep has a vital function,” Siegel says.