Migration Trail: Any Shut-eye Along the Way?
Photo: Keith Jones
a snooze near the surface?
Photo: Jane Duden
Wondering About Rest. . .
whales travel 24 hours a day. Could
they possibly make their 10,000-mile annual migration without any
rest or sleep?
Gray whales are voluntary breathers. This means they have
to think each time they take a breath. Humans don't have to do this.
basically go unconscious while we sleep and breathe automatically.
How do whales
sleep if they must be conscious to breathe?
years, scientists were unsure about these questions. They had long
whales lying motionless on the surface in an activity called logging.
Whales "log" for 20 to 30 minutes at a time, but no one knew
what was actually happening. Whales were resting during these periods,
but were they sleeping? If so, do they sleep like we do?
Looking for Answers
Sleep: The First Breakthrough
For many years, people who worked with dolphins thought these marine
mammals could shut down half their brain and rest it. The other half
would stay active.
sounded far-fetched, and scientists were skeptical about the idea. But
then a Russian scientist put this idea to the test. He placed electrodes
on the heads of bottlenose dolphins and recorded their brain waves over
time. His results showed that these dolphins did put half their brain
to rest at a time, while the other half remained active! Were whales
the same thing, allowing them to "sleep" for short periods
Whale Observations in a Sea World Pool
A team of scientists, still searching for clues
on gray whale sleep, studied a rescued gray whale in a pool at Sea World.
For nine days, they made continuous video-recordings and observations.
They collected data on the whale's behaviors. Here's what they found:
- The gray
whale rested in two ways: (1) by hanging just below the surface
its blowhole above water and (2) by lying on the bottom of the pool.
- In both
cases, the whale's breathing slowed. Its fins and tail moved
slowly until it was fully resting. Then the whale only moved to take
breaths of air.
- When the
whale rested on the bottom of the pool, it rose to the surface every
few minutes and breathed.
- At different
times, the whale slept with both eyes open, both eyes shut, and
one eye open (indicating that only half its brain was active).
- The whale
was more likely to be active during the day and resting or sleeping
sleep, the whale's body sometimes jerked and twitched. In humans
other mammals, these movements indicate a deeper state of sleep (and
Each study adds a little more to our understanding of whale sleep. But
plenty of questions remain. Here are a few:
gray whales behave the same way in their natural environment?
- Do migrating
whales rest or sleep in the same way as whales that are on feeding and
gray whales safely rest on the bottom in shallow waters?
- Do gray
whale calves have different sleep habits than adults?
- Do gray
questions do YOU have about gray whales and sleep? How
would you try to go about finding answers?