Neuroscience for Kids - Newborn Cetaceans Do Not Sleep

Newborn Dolphins and Orcas Don't Sleep
Their Mothers Don't Sleep Much Either

July 3, 2005
Mothers of newborn babies often complain that they don't get enough sleep. Human babies may sleep for up to 16 hours each day, but most babies sleep for only short periods at one time. Mothers must feed the baby and change the baby's diapers frequently -- sometimes several times during the night. Because the schedules of the baby and mother do not match, the mother may end up deprived of sleep.
At least human mothers get some sleep. The mothers of newborn dolphins and orcas (also called "killer whales") get almost NO sleep for several weeks after their calves are born. The calves themselves don't sleep at all!
Researchers in the United States and Russia studied two captive killer whale (Orcinus orca) mothers and their calves and four captive dolphin (Tursiops truncatus) mothers and their calves. The scientists recorded how much time the animals spent floating on the surface of the water or lying on the bottom of their pools. These behaviors were considered to be periods of sleep. Usually, adult orcas spend between five and eight hours sleeping each day.
The behavior of the newborn killer whales and dolphins was much different than that of adult animals. The killer whale and dolphin calves showed no sleep behavior for three weeks after they were born. As the calves got older, the amount of time they spent sleeping increased gradually. The sleep behavior of the mothers mirrored that of their newborns. New dolphin and killer whale mothers got almost no sleep for three weeks after their calves were born.
Could the animals have slept while they were swimming? The researchers point out that dolphins and beluga whales have been observed to sleep with one brain hemisphere at a time. During these periods of sleep, the eye on the opposite side of the sleeping hemisphere is almost always closed. This eye closing behavior was almost never seen in newborn dolphin and killer whale calves or their mothers for the first few weeks after the calves were born. The frequent turning and surfacing behavior of the calves also make it less likely that they got any sleep.
The lack of sleep in these dolphins and killer whales is very unusual. This behavior has not been seen in any other animals. The scientists believe that the ability to go without sleep may help the calves avoid predators and maintain their body temperature until they develop enough blubber to survive in cold water.

Did you know?

Dolphin Brain
Comparative Mammalian Brain Collection

The brain of a bottlenose dolphin weighs 1.5 to 1.6 kg.
The brain of a killer whale weighs about 5.62 kg.
The brain of an adult human weighs about 1.4 kg.
Rats that are totally deprived of sleep will die in two to three weeks. (Reference: Rechtschaffen, A. and Bergmann, B.M., Sleep deprivation in the rat by the disk-over-water method. Behav. Brain Res., 69:55-63, 1995.)

Reference and more information:

Lyamin, O., Pryaslova, J., Lance, V. and Siegel, J., Continuous activity in cetaceans after birth, Nature, 435:1177, 2005.
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