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"Penguin Ranch" Reveals Hunting, Swimming Secrets

James Owen
for National Geographic News
January 30, 2004
 
Harnessed up and ready to dive, the fat penguin looks as though it has its own mini scuba tank. Of course, emperor penguins don't need scuba tanks—they are bird-world record holders at holding their breath underwater. The device strapped to its back is, in fact, a Crittercam, one of National Geographic's animal-adapted camera systems.

It was attached by marine biologist and medical anesthesiologist Paul Ponganis, to provide, for the first time, a bird's-eye view of emperor penguins (Aptenodytes forsteri) as they hunt beneath the ice.


Ponganis, from the Scripps Institution of Oceanography in La Jolla, California, is trying to fathom out why the bird is such an amazing submariner.

For instance, why is it that emperor penguins can stay submerged for almost half an hour, longer than any other bird? And why are they able to dive well over half a kilometer down (more than 1,500 feet), far deeper than any biologist thought possible?

These are life-or-death questions, says Ponganis. Not just for penguins, but also for many critically ill humans whose lives could possibly be saved if scientists can discover the answers.

The penguins Ponganis works with live at his "Penguin Ranch," 20 miles (32 kilometers) off Ross Island, on frozen McMurdo Sound. Up to a dozen local birds are kept here temporarily before being allowed to waddle back to the wild. Their wooden fenced corral includes two dive holes. Isolated by miles of sea ice, the birds have no choice but to return to these holes after each hunting foray.

Ponganis says Crittercam doesn't impede the penguins significantly underwater, though the increased drag starts to slow them down after an hour or so. A video monitor back at the ranch shows them diving to 165 feet (50 meters) where they cruise around before accelerating towards the surface as they zero in on sub-ice fish (Pagothenia borchgrevinki). Up to six fish are caught during each dive.

"As far as I know, it was the first time feeding in the wild by an emperor penguin was actually recorded," said Ponganis, now back in California. "Documentation of this behavior was valuable because it demonstrated that even shallow foraging dives could be successful, and that the isolated dive hole is our best model for studying diving physiology."

Colleague and Antarctic veteran Jerry Kooyman, research professor at the Scripps Institution of Oceanography, was similarly thrilled with the Crittercam footage. Kooyman, a leading authority on what he calls the "icon of Antarctica," says he was surprised by the penguins' hunting success rate, and the distance at which they spotted their prey.

Biggest Penguin

Growing to over 3.8 feet (1.15 meters) tall and weighing up to 88 pounds (40 kilograms), emperor penguins are the largest of 17 penguin species. Some 200,000 pairs breed in colonies scattered across Antarctica. They are the only animals to breed here in winter. Chicks fledge in summer, when food is abundant and the weather relatively mild.

A single egg is incubated by the male while its partner heads for the sea. With the egg tucked carefully between its feet and belly, the bird huddles together with other males for warmth. They must survive horrendous gales and wind chill temperatures down to minus 76°F (minus 60°C) from the start of the breeding season until the females return. That's about four months, and without any food.

Excellent insulation is required if parent and egg are to survive. As well as four layers of scale-like feathers over a thick layer of fat, they have small bills and flippers to conserve heat.

Despite these adaptations, emperor penguins are also designed for life beneath the ice. Once in water, the birds become streamlined, athletic predators, accelerating to speeds of 16 feet per second (five meters per second). Tongues equipped with backward-facing barbs prevent fish, krill, and other prey from escaping.

But what really fascinates, and confounds, scientists is the emperor penguin's abilities as a deep-sea diver.

Recorded dives have lasted 22 minutes, and reached depths of 1,800 feet (550 meters). At 1,200 feet (366 meters) animals are subject to 40 times the barometric pressure they experience at the surface. Oxygen supply to the brain and other organs is severely restricted as air in the lungs is squeezed to a 40th of its usual volume. Huge pressures force nitrogen to dissolve in the blood, a condition which can be deadly.

If not actually crushed to death at such depths, unprotected humans would face other fatal effects, known collectively as barotrauma.

Ponganis said: "Anatomically, penguins have lost air spaces, that is their bones are solid, so they do not suffer from mechanical barotrauma. How they avoid 'the bends,' nitrogen narcosis, or high pressure nervous syndrome—common ailments among humans exposed to pressure—is unknown."

Conserving Oxygen

Scientists have a better idea why they are able to stay underwater for so long. Research by Ponganis and Kooyman suggests emperor penguins are metabolically adapted to conserve oxygen while swimming. Heart rate and body temperature measurements taken at Penguin Ranch indicate how they do this.

Ponganis said: "It had been hypothesized that hypothermia decreased metabolic rate, and that explained how penguins can dive for such long periods. However, we found that core temperature did not decline during diving, and we think that metabolic demands are lowered due to decreases in heart rate—down to 15 to 20 beats per minute in some dives."

In addition, recent studies suggest that during their descent emperor penguins cut off blood supply to much of the body. In effect, all but the most essential organs are shut down. This helps not only to conserve oxygen but reduces the risk of nitrogen getting in the bloodstream.

As a physician, Ponganis believes a deeper understanding of the emperor penguin's physiology could benefit human patients.

He said: "How their organs can survive such decreased blood flow and low oxygen levels during a dive is potentially relevant to how we might be able to treat human organs to better survive heart attacks and peripheral vascular disease because in both situations the organs experience very low blood flow and oxygen delivery."

Similarly, he says, the study of emperor penguins could enable us to preserve for longer organs intended for transplant.

They may look comical, out there on the ice, but don't be fooled. For us humans, emperor penguins could be a potential lifesaver.
 

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