Penguins
Birds that gave up flight for swimming.
Penguins are flightless seabirds of the southern hemisphere. Around 18 species range from Antarctica to the Galápagos at the equator — the common belief that they are all polar animals is wrong, and only two species breed on the Antarctic mainland.
No penguin lives in the Arctic. Penguins and polar bears never meet outside advertising.
Built for water, not air
Wings became stiff flattened flippers that cannot fold, and the bones are solid rather than hollow — heavier, which helps in diving. Flight was traded for underwater propulsion, and penguins effectively fly through water, generating thrust on both the up and down stroke.
Staying warm
- Dense overlapping feathers, roughly 100 per square inch, trapping an insulating air layer.
- A thick blubber layer beneath the skin.
- Countercurrent heat exchange in the flippers and legs: outgoing arterial blood warms incoming venous blood, so heat is recovered rather than lost at the extremities.
- Huddling — emperor penguins rotate through a huddle so individuals take turns at the cold edge.
Breeding
Emperor penguins breed through the Antarctic winter. The female lays one egg and departs to feed; the male incubates it on his feet under a brood pouch for about 65 days in temperatures below −40 °C, without eating, losing much of his body mass before she returns.