Orcas avoid being overheard by their prey by hunting in „stealth mode“, according to researchers.

The scientists wanted to know how orcas, commonly known as killer whales, communicate when hunting mammals, which can hear their distinctive calls.

The researchers thought the predators might switch to very high frequency whistles to co-ordinate the hunt.

But the orcas actually go completely silent and are somehow still able to form organised hunting groups.

Volker Deecke from the University of St Andrews in Scotland and Rüdiger Riesch from North Carolina State University in Raleigh, US, carried out the study, which was published in the journal Behavioural Ecology and Sociobiology. ….
The researchers focused on transient orcas, in the Pacific Ocean off the coast of Canada and Alaska. These tend to live in smaller social groups and to move around more than resident orcas.

Some scientists believe that the two are distinct sub-species.

„The most striking difference between the two is their diet,“ explained Dr Deecke.

Residents eat fish, whereas transients hunt and eat marine mammals, including seals and porpoises.

Dr Deecke added: „In the 40 years that these animals have been studied, scientists have never seen a resident eat a mammal and never seen a transient eat a fish

Source and more:
http://news.bbc.co.uk/earth/hi/earth_news/newsid_9409000/9409694.stm

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