Join the click for a kill or cuddle

October 15, 2004

Sperm whales have been revealed as both ruthless predators and gentle socialites in a study that lifts the lid on their hidden underwater world for the first time.

Advanced tracking devices have recorded the animals chasing down prey using bat-like echolocation as well as rubbing against each other as though cuddling.

Instruments developed by a team of scientists in Scotland and the US have captured every movement and sound emitted by 71 sperm whales tagged in the Mediterranean, the northwest Atlantic and the Gulf of Mexico.

Initial results have resolved unanswered questions about the behaviour of the animals.

The work was carried out by Patrick Miller, Royal Society international fellow at the Sea Mammal Research Unit, St Andrews University, and Mark Johnson, senior engineer, and Peter Tyack, senior scientist, at Woods Hole Oceanographic Institute in the US.

Dr Miller said: "For the first time, we actually experience the underwater world as the whale does. We are essentially riding on its back, hearing what it hears, seeing how it moves and gaining a new understanding of the components in its life."

An epoxy-coated package of instruments, the size of a cordless telephone receiver, is attached to the whale with suction cups. This pops off up to 12 hours later and floats to the surface, where it is retrieved by the scientists.

Data collected by orientation sensors and a digital sound recorder inside the package allows scientists to recreate behaviour from the sounds and movements.

The whales stick together while they are close to the surface but they dive alone, reaching depths of up to 1km. As they forage for squid and fish, they emit clicks between a half and two seconds apart. But when they detect prey, the sound changes to a creak, which is made up of much more frequent clicks. This stream of sound gives the whale fine details about what is around them and allows them to manoeuvre quickly to capture their food.

As they return to the surface, the whales interact once more, giving out precise patterns of clicks that often prompt two animals to rub together.

In one case, a mother and calf pushed against each other as they spiralled towards the surface.

"Just like it is for us, physical contact seems to be a really important part of the social life of the sperm whale," Dr Miller said.

The research is published in the Proceedings of the Royal Society B this week.

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