Subject: How do whales sleep/Why do they migrate?

Jennifer D. Philips (
Tue, 05 May 1998 20:34:25 -1000

>I need this information for a project at school. So could you please 
>answer my 2 questions.
>How do whales sleep?
>Why do they migrate?
>Tee Chow Lee
>New Zealand Student 

Hi - 

How do whales sleep?  As you know, whales have to breath air, as do all
mammals.  But because they also spend most of their time diving under the
water, they have adapted to be 'voluntary breathers', which is unlike most
other mammals.  This means that they must think about and control each
breath they take, so that their body does not attempt to take in air while
they are diving.  The same is even true while they are sleeping.  Whales
and dolphins handle this by basically sleeping "one hemisphere at a time".
Like other mammals, whales and dolphins have two halves of their brain,
each with its own functions and uses.  When one half of a whales brain is
sleeping, the other is basically conscious and is in control of breathing.
During rest, whales tend to be very  inactive, resting close to or at the
surface.  When a breath is needed, the brain is conscious enough to cause
the whale to swim to the surface and take a breath.  Whales and dolphins
never enter a deep sleep, and they never enter that time of sleep during
which other mammals would be dreaming, called REM sleep.  

Why do whales migrate?  This is a result of the overall niche that whales
fill - in other words, whales are very large animals, but they eat very
small, abundant crustaceans called krill.  Krill is most abundant in very
cold waters, so because whales need to eat so much in order to sustain
their body, they must go where the krill are.  BUT, whales also must give
birth to their young, and they must do it in the water.  To maximize the
chance that their young will survive, they must give birth in warm, calm
seas.  They cold northern waters may have krill but they are neither warm
nor calm!  So whales migrate so that they can be in the right place at the
right time.  They go to the cold waters to feed at the right time of the
year and they travel thousands of miles away to the warm waters to give
birth, nurse their new young, and mate again.  

I hope this answers your questions!  Good luck on your project!

Aloha - 



Jennifer D. Philips

Marine Mammal Research Program
HIMB, University of Hawaii at Manoa
PO Box 1106			
Kailua, HI  96734
voice:  (808) 247-5063
fax: (808) 247-5831