Underwater they can swim up to 25 mi (40.3 km) per hr as they pursue the fish, squid, and shrimp that form their diet. They do not eat while on land, subsisting on a layer of fat under the skin this results in weight losses of up to 75 lb (33.8 kg) during the two-month incubation period. Their chief enemies are the leopard seal, killer whale, and skua gull. Penguins are highly gregarious, and a population density of half a million birds in 500 acres has been counted at a colony in Antarctica.
There are 17 species of penguins, 10 of which are considered endangered or threatened. The largest penguins, the emperor and the king (3–4 ft/91.5–122 cm in height), incubate their eggs between their feet in a fold of skin. The smaller jackass penguins, Spheniscus demersus, are named for their braying cry, and crested penguins (genus Eudyptes ) are distinguished by yellow plumes on either side of the head. Smallest of all is the little blue penguin, Eudyptula minor, of New Zealand and Australia, which is 16–17 in. (41–44 cm) tall. Other penguins also live in more northerly waters, such as the Galápagos penguin Spheniscus mendiculus, found in equatorial waters.
Penguins are classified in the phylum Chordata , subphylum Vertebrata, class Aves, order Sphenisciformes, family Spheniscidae.
See E. G. Simpson, Penguins, (1982).
See more Encyclopedia articles on: Vertebrate Zoology
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