Published online 14 December 2007 | Nature | doi:10.1038/news.2007.380

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A pack of killer whales uses waves to knock seals off the ice.

Several orcas work together to make a wave that will wash this seal into the water. Courtesy of the researchers

Some Antarctic orcas use the cunning tactic of regularly hunting in packs and making waves to wash seals off floating ice, researchers have confirmed.

The behaviour was first seen in 1979, but at the time it was considered a one-time moment of orca ingenuity. Now, Ingrid Visser of the Orca Research Trust in New Zealand and her colleagues report on six further observations of the animals using group hunting behaviour to divide ice floes, push them into open water, and create waves to wash animals off them into their waiting jaws. The behaviour has been seen only along the Antarctic Peninsula and nowhere else in the world, they note, including other icy orca habitats in the Arctic and Antarctic. The report is published1 in the journal Marine Mammal Science, and a recent video of the behaviour is available on You Tube (with the key moment happening 2 minutes 40 seconds into the tape).

It is not the first time a complex behaviour has been seen in just a few orcas. In the early 1970s, an orca was seen in Argentina beaching itself next to seals. At first it seemed to be in distress, but then it lunged at seals nearby, grabbed one by the neck, and dragged it back into the water. This beaching hunting technique has since been observed hundreds of times in Argentina among a small group of orcas. Studies have shown that the orcas can time their forays onto land to coincide with the tides, so they run less risk of becoming permanently beached.

Hunting school

Both the beaching and the wave hunting seem to be techniques that pod elders teach to younger animals. The Argentinean orcas have been seen nudging youngsters onto the shore, encouraging them to try the tactic, often coming up alongside to demonstrate. In the group at the Antarctic Peninsula, young orcas are often present during the hunt, and adults sometimes put living seals back on the ice after catching them, seemingly so that the young can have another try.

“This is orca culture,” says Visser.

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The unique cultural characteristics of different orca pods may spur a reconsideration of their conservation status says Astrid van Ginneken at the Center for Whale Research in Friday Harbor, Washington.

Orcas (Orcinus orca) are not considered an endangered or threatened species; they are found in all the world's oceans. Some local populations, however, are threatened by changes to their habitat. Whether subsets of orcas with unique cultures should be considered separately is a matter that has not really been dealt with, she says. “Distinct social populations with specialized traditions are far more at risk than the genetic population, and our conservation policies need to reflect that,” says van Ginneken.