Birds
Penguin
Spheniscidae · also called penguins
A penguin is a bird that gave up the sky for the sea. Its wings no longer bend or fold; they are stiff flippers that beat underwater in a stroke that is genuinely flapping flight, just in a denser medium. Everything else — the heavy bones, the fat, the packed feathers, the upright waddle — follows from that one decision.
Overview
Penguins are the family Spheniscidae, around 18 species, all in the Southern Hemisphere. They range from the 1 kg little penguin to the emperor penguin at nearly 40 kg. Every species is flightless, superbly adapted to cold seas, and comes ashore only to breed and moult. They eat fish, krill, and squid caught on dives.
Flippers, ballast, and a warm core
A penguin’s wing is a flattened, near-rigid paddle driven by large flight muscles. Its bones are solid rather than hollow, cutting buoyancy so diving costs less effort. Emperor penguins reach depths beyond 500 m and hold their breath over 20 minutes, dropping the heart rate to a few beats a minute. Warmth comes from the densest feather coat of any bird, a fat layer beneath, and heat-exchange plumbing in the legs and flippers.
Breeding at the edge of the possible
Penguin breeding is built around long fasts and shared shifts. A male emperor balances the egg on his feet through the Antarctic winter for about 65 days without food, huddling with thousands of others and losing nearly half his weight. Most other species nest in dense colonies on rock or in burrows, both parents taking turns to incubate and to make long foraging trips.
A southern family in decline
Despite the polar image, many penguins live in temperate or tropical seas, and more than half of all species are now threatened or near threatened. The African, Galapagos, yellow-eyed, and northern rockhopper penguins are falling fast, hit by overfishing of their prey, warming and shifting currents, introduced predators, and oil spills.
Status
Penguins as a family are Not Evaluated, but the overall trend is decreasing, and several species could be lost within decades without changes to fishing and stronger protection of their colonies and feeding grounds.
Penguin: common questions
Why can't penguins fly?
Because they became so good at swimming instead. Flight and diving pull a wing in opposite directions, since flying rewards a large, light, flexible wing and a buoyant body, while diving rewards a small, stiff paddle and a heavy body that sinks easily. A penguin's ancestors, which could fly, gradually shifted all the way to the swimming end, flattening the wing into a flipper, filling in the bones, and packing on fat and muscle. Related birds such as the auks of the north show the halfway point, still flying but only just. For a penguin the trade has paid off, giving it access to food no flying seabird can reach.
How do penguins stay warm in freezing water?
With several layers working together. The outer coat is the densest of any bird, made of short stiff feathers packed 15 or more to the square centimetre, each with a downy base, and kept oiled and overlapping so that water and wind barely reach the skin. Under that lies a thick pad of fat. Blood vessels going to the feet and flippers run alongside the returning vessels and hand over their heat on the way, so the extremities stay just above freezing without draining warmth from the core. On land, penguins huddle in tight groups that cut each bird's heat loss dramatically and share the coldest outer positions.
Do penguins mate for life?
Many stay with the same partner from one year to the next, but it is not the lifelong bond it is sometimes described as. Reunion rates vary a lot by species, from around 15 per cent in emperor penguins, who have no fixed nest site to meet at, to 80 per cent or more in some smaller species that return to the same burrow. Pairs that raise chicks successfully are more likely to stay together, and birds will divorce after a failed breeding season or if a partner arrives late. Within a season most penguins are faithful, and both parents share incubation and feeding.
Are there penguins at the North Pole?
No wild ones, and there never have been. Every penguin species lives in the Southern Hemisphere, and while several are nowhere near ice, living in South Africa, southern Australia, or the Galapagos, none has crossed the warm tropical seas to reach the north. The Arctic has its own unrelated diving birds, the auks, including puffins, guillemots, and the extinct great auk, which fill a similar role and look superficially alike through convergent evolution. The great auk was even originally called a penguin, and the southern birds took the name later.