Saturday, December 15, 2007

Killer Whales

Unique orca hunting technique documented
A pack of killer whales uses waves to knock seals off the ice.

Matt Kaplan

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


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