From the ArcaMax Publishing, Trivia Newsletter:
http://www.arcamax.com/news/trivia/s-293635-980337
Orca whales are voluntary breathers. For this reason, they sleep with only half of their brain at one time. The other half remains alert to regulate breathing. Resident whales typically remain near the surface, breathing and swimming in a pattern. When traveling together, resident pods have been observed to breathe in unison. Although it is not known why this occurs, it could be a way of helping the pod keep tabs on one another.
This news arrived on: 01/26/2008