Dolphins Don't Sleep
by Emily Hager
In the search to understand why we need a certain amount
of sleep, scientists have discovered that dolphins and
killer whales survive on almost no sleep for the first
months of life. This ScienCentral News video has more.
The Young and the Restless
a new mother is exhausting, but if you're a dolphin or
a killer whale, you may not be getting any extra sleep-time
to recover, in fact you may not be getting any sleep at
all. Scientists in California and Russia have discovered
that both dolphin and killer whale mothers and calves
apparently go with no sleep for the first few months of
the new baby's life.
"These marine [animals], who are mammals
like us, thrive without any extended periods of sleep
for over a month," says lead researcher and neuroscientist
Sepulveda VA Ambulatory Care Center Jerome
Siegel and his colleagues monitored two
killer whale and calf pairs at SeaWorld
San Diego, as well as four dolphin and calf pairs
at the Gelendgick Dophinarium near Russia's Black Sea
coast. They reported in the journal Nature
that during the first postpartum month these animals were
awake "24 hours a day," but gradually increased
the amount of time they spent sleeping as the calf aged.
"We all feel like, they must be incredibly
tired, but they don't seem to be," says SeaWorld's
senior veterinarian Jim McBain, who witnessed much of
Siegel's team's research on the killer whales.
Siegel says the sleep patterns he and his
colleagues observed in the babies are "just the reverse"
of all other mammals, which normally sleep the most after
birth and gradually taper down to adult levels as they
age. "This is a challenge for the idea that sleep
is necessary for brain and body growth, because during
this period of very rapid development in killer whales,
and we've also seen it in dolphins," says Siegel,
"There's actually the lowest level of sleep behavior
of the animals' entire life."
The researchers do not know how the mothers
and their babies can live on so little sleep, though they
expect it's a behavior the babies evolved to keep moving
and stay warm and safe in colder, wilder waters. For the
mothers, it is most likely part of their protective nature
and also to create what's called a "slipstream"
beneath their bellies where their calves, who are not
very strong swimmers, can coast through the water easily.
But dolphins and killer whales — members
of what scientists call the larger marine mammal order
— are known for their minimal sleep habits. In the
wild, adult cetaceans sleep with one eye open. Research
State University marine biologist Dawn
Goley and Siegel's colleague Oleg
Lyamin have shown that when cetaceans have their right
eye closed, the left side of their brain is asleep, and
vice versa. According to the research, this "uni-hemispheric"
sleep is associated with slow, inactive brainwaves in
the sleeping part of the brain.
Stone, Vice President for Global
Marine Programs at the New
England Aquarium, says it's similar to lazing in a
hammock on a Sunday afternoon, "When you go half
asleep and shut some of your circuits down."
Stone says, "We didn't see any eye
closure during this early period after birth in either
the mother or the new born, which is what convinced us
that even by the standards of [cetacean] sleep, they're
not having the brain activity pattern seen in sleep."
Cetaceans sleep this way because unlike
humans, they have to make a conscious effort to breath.
Keeping half of their brain awake, allows them to be alert
enough to surface and breathe as well as being aware of
Though there are few dangers at places
like SeaWorld, the researchers say the behavior they observed
has nothing to do with the animals being in captivity,
and that wild dolphins and killer whales probably behave
"The ocean is a very different kind
of environment from land," says Siegel. "There's
no safe place to sleep in the ocean, [and] there's no
warm place to sleep in the ocean, so these two factors
may account for the animals' behavior."
McBain says, "If an animal is going
to have a chance to sleep more, it would be here at SeaWorld
[rather] than it would be in the wild."
Stone also agrees that this is an evolutionary
behavior that "transcends" the animals' environment.
"I can't imagine why they would have a different
sleep pattern in captivity than in the wild," says
But there's a different way to interpret
these "compelling" findings says Dawn Goley.
"Either they don't sleep or they sleep in shorter
bouts of time," she says.
In order to better understand their sleep
patterns, Goley says the researchers need to do a neurological,
not just a behavioral analysis, of the animals. She says
remotely monitoring the brainwaves of the animals would
help further the understanding of their sleep behavior.
As their work progresses, the researchers
plan to study killer whale and dolphin brains to see if
there is a structural explanation for their sleep habits,
as well as to determine if changes in brain chemistry
might be limiting their sleep after birth. If they can
unravel this mystery, they may ultimately have a better
understanding of why we humans need sleep, what it takes
to go without it, and how to treat sleeping disorders.
This research was published in the June
30, 2005 issue of Nature, and was funded
by the National
Institutes of Health, the National
Science Foundation, Department
of Veterans Affairs, Utrish Dolphinarium and DARPA.
Original source: http://www.sciencentral.com