Penguins (order Sphenisciformes, family Spheniscidae) are a group of aquatic, flightless birds living almost exclusively in the southern hemisphere, especially in Antarctica. Highly adapted for life in the water, penguins have countershaded dark and white plumage, and their wings have evolved into flippers. Most penguins feed on krill, fish, squid and other forms of sealife caught while swimming underwater. They spend about half of their lives on land and half in the oceans.
Although all penguin species are native to the southern hemisphere, they are not found only in cold climates, such as Antarctica. In fact, only a few species of penguin live so far south. Several species are found in the temperate zone, and one species, the Galápagos Penguin, lives near the equator.
The largest living species is the Emperor Penguin (Aptenodytes forsteri): on average adults are about 1.1 m (3 ft 7 in) tall and weigh 35 kg (75 lb) or more. The smallest penguin species is the Little Blue Penguin (Eudyptula minor), also known as the Fairy Penguin, which stands around 40 cm tall (16 in) and weighs 1 kg (2.2 lb). Among extant penguins, larger penguins inhabit colder regions, while smaller penguins are generally found in temperate or even tropical climates (see also Bergmann's Rule). Some prehistoric species attained enormous sizes, becoming as tall or as heavy as an adult human. These were not restricted to Antarctic regions; on the contrary, subantarctic regions harboured high diversity, and at least one giant penguin occurred in a region not quite 2,000 km south of the equator 35 mya, in a climate decidedly warmer than today.
Etymology
The word "Penguin" first appears in the 16th century as a synonym for Great Auk. It may be derived from the Welsh pen gwyn "white head", although the etymology is debated. When European explorers discovered what are today known as penguins in the Southern Hemisphere, they noticed their similar appearance to the Great Auk of the northern hemisphere, and named them after this bird, although they are not related.
The etymology of the word "penguin" is still debated. The English word is not apparently of French, nor of Breton or Spanish origin (both attributed to the French word pingouin "auk"), but first appears in English or Dutch.
Some dictionaries suggest a derivation from Welsh pen, "head" and gwyn, "white", including the Oxford English Dictionary, the American Heritage Dictionary, the Century Dictionary and Merriam-Webster, on the basis that the name was originally applied to the great auk, either because it was found on White Head Island (Welsh Pen Gwyn) in Newfoundland, or because it had white circles around its eyes (though the head was black).
An alternative etymology links the word to Latin pinguis which means "fat". In Dutch the alternative word for penguin is 'fat-goose' ('vetgans' see: Dutch wiki or dictionaries under Pinguïn), and would indicate this bird received its name from its appearance.
Anatomy and physiology
All penguins are countershaded for camouflage – that is, they have black backs and wings with white fronts. A predator looking up from below (such as an orca or a leopard seal) has difficulty distinguishing between a white penguin belly and the reflective water surface. The dark plumage on their backs camouflages them from above.
Diving penguins reach 6 to 12 km/h (3.7 to 7.5 mph), though there are reports of velocities of 27 km/h (17 mph) (which are more realistic in the case of startled flight). The small penguins do not usually dive deep; they catch their prey near the surface in dives that normally last only one or two minutes. Larger penguins can dive deep in case of need. Dives of the large Emperor Penguin have been recorded reaching a depth of 565 m (1,870 ft) for up to 22 minutes.
Penguins either waddle on their feet or slide on their bellies across the snow, a movement called "tobogganing", which conserves energy while moving quickly. They also jump with both feet together if they want to move more quickly or cross steep or rocky terrain.
Penguins have an average sense of hearing for birds; this is used by parents and chicks to locate one another in crowded colonies. Their eyes are adapted for underwater vision, and are their primary means of locating prey and avoiding predators; in air it has been suggested that they are nearsighted, although research has not supported this hypothesis.
They can drink salt water because their supraorbital gland filters excess salt from the bloodstream.[ The salt is excreted in a concentrated fluid from the nasal passages.
The Great Auk of the Northern Hemisphere, now extinct, was superficially similar to penguins, and the word "penguin" was originally used for that bird, centuries ago. They are not related to the penguins at all, but are an example of convergent evolution.
Isabelline penguins
Perhaps one in 50,000 penguins (of most species) are born with brown rather than black plumage. These are called isabelline penguins. Isabellinism is different from albinism. Isabelline penguins tend to live shorter lives than normal penguins, as they are not well-camouflaged against the deep, and are often passed over as mates.
Distribution and habitat
See also: List of Sphenisciformes by population
Although all penguin species are native to the southern hemisphere, they are not found only in cold climates, such as Antarctica. In fact, only a few species of penguin actually live so far south. At least 10 species live in the temperate zone; one, the Galápagos Penguin, lives as far north as the Galápagos Islands, but this is only made possible by the cold, rich waters of the Antarctic Humboldt Current that flows around these islands.Several authors have suggested that penguins are a good example of Bergmann's Rule where larger bodied populations live at higher latitudes than smaller bodied populations. There is some disagreement about this, and several other authors have noted that there are fossil penguin species that contradict this hypothesis and that ocean currents and upwellings are likely to have had a greater effect on species diversity than latitude alone.
Major populations of penguins are found in Antarctica, Argentina, Australia, Chile, New Zealand, and South Africa.
Behaviour
Breeding
Penguins for the most part breed in large colonies, the exceptions being the Yellow-eyed and Fiordland species; these colonies may range in size from as few as a 100 pairs for Gentoo Penguins, to several hundred thousand in the case of King, Macaroni and Chinstrap Penguins. Living in colonies results in a high level of social interaction between birds, which has led to a large repertoire of visual as well as vocal displays in all penguin species. Agonistic displays are those intended to confront or drive off, or alternately appease and avoid conflict with, other individuals.Penguins form monogamous pairs for a breeding season, though the rate the same pair recouples varies drastically. Most penguins lay two eggs in a clutch, although the two largest species, the Emperor and the King Penguins, lay only one. With the exception of the Emperor Penguin, where the male does it all, all penguins share the incubation duties. These incubation shifts can last days and even weeks as one member of the pair feeds at sea.
Penguins generally only lay one brood; the exception is the Little Penguin, which can raise two or three broods in a season.
Penguin eggs are smaller than any other bird species when compared proportionally to the weight of the parent birds; at 52 g (2 oz), the Little Penguin egg is 4.7% of its mothers' weight, and the 450 g (1 lb) Emperor Penguin egg is 2.3%. The relatively thick shell forms between 10 and 16% of the weight of a penguin egg, presumably to minimise risk of breakage in an adverse nesting environment. The yolk, too, is large, and comprises 22–31% of the egg. Some yolk often remains when a chick is born, and is thought to help sustain it if parents are delayed in returning with food.
When mothers lose a chick, they sometimes attempt to "steal" another mother's chick, usually unsuccessfully as other females in the vicinity assist the defending mother in keeping her chick. In some species, such as Emperor Penguins, young penguins assemble in large groups called crèches.
