Bird Fact Friday – Emperor Penguins

Adapted from pages 174-176 of Far From Land:

Diving to any sub-surface feast necessarily poses problems. An obvious problem is that, when underwater, the bird cannot breathe and must eke out those oxygen stores with which it submerges for as long as possible. The adaptations that help the diving bird overcome this difficulty has been most extensively studied in Emperor Penguins.

Given its size, and therefore predictable rate of oxygen consumption, an Emperor Penguin could remain underwater for about five minutes if its body processes continued to function as they do when it is breathing air. This ‘limit’ is comfortably exceeded by recorded dives lasting some 20 minutes. Just as a breathless athlete striving for the finishing line builds up lactic acid, so the underwater penguin builds up lactate, principally in the muscles. This is then flushed out when it returns eventually to the surface.

Another key adaptation to diving is a reduction in heart rate underwater, exactly as also occurs in diving seals and whales. Detected via attached electrocardiogram (ECG) recorders, the heart rate of a resting Emperor Penguin is around 70 beats/minute. This value roughly doubles immediately before the dive. If the dive is short, under five minutes, the underwater rate is about the same as when resting. If the dive is long, heart rate drops off dramatically, and may reach as low as three beats/minute. Just before the penguin surfaces, the rate accelerates. It can be around 200 beats/minute when the penguin surfaces and can breathe once more to replenish its oxygen stores.

Emperor Penguins are probably the deepest-diving of all seabirds, sometimes plumbing depths in excess of 500 m in pursuit of fish and squid. Illustration by: Bruce Pearson

Remembering that even in tropical seas, the water temperature below 200 m is probably no higher than 5°C, a further physiological problem faced by seabirds underwater is potentially that of cold. Penguins and auks have tight plumage that retains air close to the skin. This assists heat retention, albeit by creating buoyancy that hinders the downward dive. The situation is different in cormorants and shags. Their plumage is notoriously wettable. Think of the classic pose of a perched cormorant hanging out its wings to dry after a spell of swimming. If the water has reached the skin, the cormorant will have lost more heat than another seabird whose skin remains dry. How they retain heat became evident when European researchers looked at the plumage more closely. All four subspecies studied, living in sub-Arctic to subtropical climes, retained an insulating air layer in their plumage, which was, however, much thinner than for other species of diving birds. Detailed examination of the plumage showed that each cormorant body feather has a loose, instantaneously wet, outer section and a highly waterproof central portion.

Far From Land
Michael Brooke
With illustrations by Bruce Pearson

Seabirds evoke the spirit of the earth’s wildest places. They spend large portions of their lives at sea, often far from land, and nest on beautiful and remote islands that humans rarely visit. Thanks to the development of increasingly sophisticated and miniaturized devices that can track their every movement and behavior, it is now possible to observe the mysterious lives of these remarkable creatures as never before. This beautifully illustrated book takes you on a breathtaking journey around the globe to reveal where these birds actually go when they roam the sea, the tactics they employ to traverse vast tracts of ocean, the strategies they use to evade threats, and more.

Michael Brooke has visited every corner of the world in his lifelong pursuit of seabirds. Here, he draws on his own experiences and insights as well as the latest cutting-edge science to shed light on the elusive seafaring lives of albatrosses, frigatebirds, cormorants, and other ocean wanderers. Where do puffins go in the winter? How deep do penguins dive? From how far away can an albatross spot a fishing vessel worth following for its next meal? Brooke addresses these and other questions in this delightful book. Along the way, he reveals that seabirds are not the aimless wind-tossed creatures they may appear to be and explains the observational innovations that are driving this exciting area of research.

Featuring illustrations by renowned artist Bruce Pearson and packed with intriguing facts, Far from Land provides an extraordinary up-close look at the activities of seabirds.

This post is part of a series, explore additional posts here<< Bird Fact Friday – Virginia’s Warbler