Two blue whales filter feeding at sea surface.

Two blue whales (Balaenoptera musculus) feed on krill in the Pacific Ocean off the coast of California. Credit: Doc White/

Animal behaviour

When blue whales ignore their rightward leanings

World’s biggest mammals take sides when catching prey.

Much as humans do, blue whales usually favour their right side — but they switch to their left to gain an advantage over prey.

Blue whales (Balaenoptera musculus) feed on tiny marine creatures called krill by rolling to one side while swimming with their mouths agape. Ari Friedlaender, currently at the University of California, Santa Cruz, and his colleagues used motion sensors to track 63 blue whales off the coast of California.

The team found that most whales preferred to roll to the right as they hunted. But many preferred to roll left in shallow waters, where krill patches are smaller and less dense.

The leftward rolls allowed the whales to see the krill patches with their right eye. The right eye sends visual information to the left hemisphere of the brain, which is responsible for coordination, movement and planning.

Ignoring their innate preference could help blue whales to capture prey more efficiently, the authors say.