Most of the world's tundra biome is found in the north polar region, where it's called Arctic tundra. A small amount of tundra also exists on Antarctica. Survival in the tundra isn't easy. Soil is frozen, its top surface thawing only in the summer. Trees can't grow. Remarkably, numerous plants and animals have adapted and thrive, including penguins. Of the 17 penguin species worldwide, four breed on the Antarctic continent -- the Adelie, Chinstrap, Gentoo and Emperor.
Early Arctic explorers mistakenly classified penguins as fish, perhaps because the birds are so adept in the water. Their breastbones make excellent keels, and massive paddling muscles propel them at speeds up to 25mph. They're masters at "porpoising," leaping clear of the water every few feet at sea and onto raised ice edges and rock ledges at substantial heights. Flightless, penguins spend as much as 75 per cent of their lives in the water. Their bodies are insulated by thick blubber, and their dense plumage is waterproof. Some penguins dive to depths of 1000 feet or more, remaining submerged for up to 25 minutes.
All penguins breed on land or sea ice attached to land. Most breed in large, dense colonies called "rookeries." Some rookeries have more than 180,000 birds so the sights, sounds and smells are unforgettable. Most penguins build nests of stone and incubate one or two eggs. In most cases, adult pairs take turns incubating the eggs and feeding the chicks once they've hatched. Communication within rookeries is extremely critical for locating mates and offspring, for courting rituals and for signalling danger. In addition to vocal signals, penguins communicate by head and flipper waving, bowing, gesturing and preening.
Penguins are enjoying a population boom. This is partly attributed to the past overfishing of baleen whales, which resulted in a superabundance of krill, shrimp-like marine crustaceans that serve as penguin food. Aside from krill, penguins feed heavily on other crustaceans, fish and squid. Penguins have few natural enemies, but these do include seals, killer whales, and in the case of young chicks and eggs, several sea bird species. Healthy adult penguins have no predators on land. Interestingly, because of this, they have no natural fear of humans. Luckily for them, humans usually leave them alone.
The world's largest penguin, the Emperor, is the only penguin to remain in Antarctica permanently. Females lay a single egg in the coldest time of year, when temperatures plummet to minus 80 degrees Fahrenheit and winds rage up to 112mph. They pass their egg to their mates and go off to sea to feed. Males don't eat during the nine-week incubation period. They warm the eggs by balancing them on their feet where they're insulated by "brood pouches," thick rolls of feathers and skin. When females return after eggs have hatched and young have been warmed in brood pouches, males -- minus up to 1/3 of their body weight -- make long 60-mile treks over the ice to find food.