Summary
4 March 2011
Orcas are usually highly communicative killer whales, but researchers from St Andrews University have found out that they hunt in complete silence to avoid being overheard by their prey.
Reporter:
Victoria Gill
Orcas - also known as killer whales - usually hunt in groups
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Killer whales whistle to talk to each other and click to find their way around. It's the echoes from these clicks that help the animals to map their surroundings and to pinpoint the location of their next meal.
But while one type of killer whale eats fish, the other hunts marine mammals, including seals and porpoises. A shoal of salmon can't hear the clicking of an approaching killer whale, but the mammals, with their highly sensitive underwater hearing, can.
The researchers used underwater microphones to listen to killer whales hunting seals off the coast of Alaska. They found that the animals fell completely silent when they were hunting. But, somehow, they still managed to organise themselves into groups - often spreading out up to a mile apart, before coming back together and calling loudly to each other while they shared their catch.
The scientists now hope to attach satellite trackers to individual killer whales, to find out more about this stealthy behaviour.
Victoria Gill, 大象传媒 News
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Vocabulary
- whistle
make a loud, high sound
- echoes
sounds which can be heard to repeat after the original noise has stopped
- surroundings
the area around a person or animal
- to pinpoint
to search and find
- mammals
certain types of warm-blooded animals (e.g. humans, dogs)
- shoal
large group of fish, swimming together
- fell silent
became completely quiet
- spreading out
separating to cover a wider area
- catch
food caught while hunting
- stealthy
moving about in a careful way, trying not to be seen
