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Underwater Penguin Action Captured
By Jennifer Viegas, Discovery News

March 31, 2004 — Marine biologists have obtained the first direct evidence for what penguins do underwater, and the data comes from a surprising source: penguins photographing other penguins.

The images were snapped from miniature digital cameras placed on the backs of Adélie (Pygoscelis adeliae) and chinstrap (P. antarctica) penguins near Signy Island, Antarctica. The study represents the first use of minicams on penguins.

The birds’ eye view photos reveal that penguins spend most of their underwater time searching for food with other penguins, and suggest that certain penguins swim and dive closely with other penguins during half of all foraging trips.

Akinori Takahashi, who led the research project and is a scientist at the National Institute of Polar Research in Japan, told Discovery News why penguins appear to prefer group swims over solo dives.

“Group behavior may help penguins to reduce the risk of predation in two ways,” Takahashi explained. “First, an individual penguin in a group could use the vigilance of its group-mates to increase the probability of detecting predators, such as seals. Second, an individual penguin in a group could decrease the chance to be preyed upon through dilution effect, meaning too many penguins for a predator.”

Takahashi added that penguins also could help each other in herding their prey, which, for the study birds, was almost exclusively Antarctic krill. Krill are small, shrimp-like crustaceans located near the base of the area’s food chain.

On average, she said birds would dive in groups ranging from one to eleven penguins. They can dive at depths over 590 feet.

In addition to showing the penguins foraging and diving in groups, the photographs revealed that, underwater, the penguins engage in porpoising, where they will zoom like mini torpedoes just below the surface before leaping out of the water and going under again. They also exhibited resting behavior, but did not appear to play underwater during the research.

Yasuhiko Naito, a colleague of Takahashi’s and one of the paper’s co-authors, developed the “penguin cam,” which also can be used on other marine mammals. Before this study, similar cameras were placed on blue whales, monk seals, sea turtles, sharks, sperm whales, and Weddell seals.

Daniel Costa, professor of ecology and evolutionary biology at the Long Marine Laboratory at the University of California at Santa Cruz, has used what he calls “crittercams” before, including work on a television special about New Zealand sea lions.

Costa agreed that Takahashi’s study presents the first images captured by penguins. He thinks that penguins dive in groups primarily to give them an edge over krill colonies.

“Schooling prey has an advantage over a solitary predator,” Costa said. “Predators can diffuse the advantage of schooling by foraging in groups. This is just like a wolf pack, a killer whale pod, or a school of dolphins.”

Costa next plans to deploy a tiny camera system on coyotes, while Takahashi and her colleagues hope to look at the density of krill populations to better understand the Antarctic food web and to help in penguin conservation.