By Ruairidh Villar
TOKYO (Reuters) - Fish of the Antarctic, be very afraid. There's an unlikely stealth predator on the loose - Adelie penguins.
Forget their ungainly waddling on land or comical bobbing at the ocean's surface. As soon as these penguins dive into the icy Antarctic ocean, they become calculating, efficient killing machines, say Japanese researchers.
"You could say the penguins have an amazing stealth mode," said Yuuki Watanabe, a researcher at Japan's National Institute of Polar Research. "They're great at sneaking up on their prey and taking them unaware."
Watanabe this week released footage recorded in December 2010 showing a bird's eye view of a hunt for fish and small crustaceans called krill, captured using a small video camera strapped to the backs of more than a dozen penguins.
"The krill wiggle their bodies about, they clearly make an attempt to swim off at full speed and escape," Watanabe said of his findings, published in the U.S.-based Proceedings of the National Academy of Sciences this week.
"But that doesn't make the slightest difference to the penguins. They just gobble up the krill that are trying to get away and swallow them whole."
Using the "penguin cams," which were set to automatically switch on when a penguin entered the water and shoot for 90 minutes, Watanabe and his team were able to capture the secrets of penguins on the hunt.
Additional information came from two accelerometers strapped to each bird that measured its head and body movements to calculate how fast it devoured its prey.
"We didn't really know if the penguins caught krill one-by-one. I'd thought that maybe they just got into their stomachs when they were after some other prey," Watanabe said. "But when we saw the footage it turned out the penguins were doing just that, eating these tiny little creatures one after the other."
Not only that, the penguins didn't swim randomly but hung poised on the edge of the ice until a thick swarm neared, then swooped into the water. Footage showed a penguin zooming under the ice and then deeper, its head snapping rapidly up as it fed.
The krill killing-rate was both fast and efficient. The penguins gobbled an average of two krill per second when the krill were clustered in swarms, a much faster rate than under general hunting conditions when the penguins consumed about 244 krill in roughly 90 minutes.
"I was so happy when I got the footage of a penguin going straight into a swarm of krill and gorging itself," Watanabe said.
Penguin research completed, Watanabe now aims to repeat the same exercise with sharks.
(Writing by Elaine Lies, Editing by Michael Perry)