Wed 9 Aug 2006

IAN JOHNSTON SCIENCE CORRESPONDENT

KILLER whales sing with their own distinctive style of song, new research has revealed.

Group calls to signal changes of movement while hunting and other messages have been found to be delivered with an "individual signature", according to a team of academics from St Andrews University and two American institutions.

This communication ability appears to put killer whales on a par with chimpanzees and bottlenose dolphins, who similarly customise group signals.

The animals were tracked as they swam in the Johnstone Strait, off British Columbia, and their calls were recorded by an underwater array of "hydrophones". Laser range finders were also used to help identify which animal was making any given call.

Anna Nousek, the lead researcher who works at both St Andrews and Florida State universities, says the study has produced the "first indication that shared killer whale calls contain some degree of individual signature information".

In a Royal Society paper published today, she writes: "This study has shown variations within shared call types, with strongly recognisable group signatures and less prominent individual signatures, which may allow both efficient transmission of group-level information and individual identity discrimination.

"Less-distinctive cues may suffice for individual recognition, as a receiver has only to discriminate among a few group members.

"Calls of individuals from different matrilines [groups related through the female line] were much more strongly distinguishable."

Killer whales have been so called for at least 2,000 years - in the 1st century the Roman scholar, Pliny the Elder, wrote: "A killer whale cannot be properly depicted or described except as an enormous mass of flesh armed with savage teeth."

However, they are now also known by a less pejorative name, orca.

It is thought superior communication skills may have developed to help killer whales hunt in groups.

They live in highly stable family groups, called pods, that share a common female ancestor. Pods that share any calls are said to belong to the same clan.

Social animals often make noises, such as warning cries, that are unique to their own group.

The Royal Society paper says: "Many behaviours, such as direction changes or co-operative foraging, may involve all the group members. In such contexts, a group-specific call may enable each group member to extract the relevant information from the background calls from other groups."

Individual identification appears in animals such as chimpanzees and bottlenose dolphins, which are generally regarded as more intelligent. While the greater spear-nosed bat makes group-specific screeches, they are not used to identify individuals.

However, the scientists say they wanted to check whether the killer whales were actually able to tell the difference between the different kinds of calls detected by the scientists' equipment.

"Signatures at different social levels must ultimately be tested using playback experiments to determine whether killer whales themselves perceive and respond to the reported differences," the paper says. "However, the presence of individual signatures strong enough to be distinguished with statistical analysis suggests the potential for individuals to acoustically distinguish between the highly similar shared calls of their matrilineal relatives."

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