The Unfeathered Bird

500 years after Leonardo, the mechanics of bird flight still enthralls.

(Katrina van Grouw)

Little Penguin

(Katrina van Grouw)

Part of penguins’ appeal is our inclination to sympathize with them,. We see them as mini-humans, unable to fly and making the best of a cold climate, instead of as the highly specialized seabirds they are. Flying and swimming have conflicting demands. Flying requires lightness and a large wing area, whereas the optimal conditions for swimming are increased body weight and, for wing-propelled birds, a small wing area. In an environment free from terrestrial predators there is little selective advantage in retaining the powers of flight. It takes little more effort to propel a large streamlined body underwater than a small one, so body size was able to develop independently of wing size, leaving penguins with wings often disproportionately small. Meanwhile, wing area was able to decrease. The long primary and secondary feathers necessary for flight play no part in underwater locomotion and merely hamper a bird’s progress. Penguins have neither, leaving them with a wing area that is small and narrow—ideal for swimming. Pictured at right: A baby penguin.

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