Penguins (order Sphenisciformes, family Spheniscidae) are an order of flightless birds living in the southern hemisphere. They are not, contrary to popular belief, only found in cold climates, such as Antarctica. Many species live as far north as the Galapagos Islands and will occasionally cross the equator while feeding.
Penguins like to stay and move within large groups. Most penguins live off krill, fish, squid, and other forms of sealife that they catch while swimming underwater. They spend half of their life time on land and half in the oceans.
The largest species is the Emperor Penguin: adults average about 1.1 meter tall and mass 30 or more kilograms. The smallest penguin species is the Little Blue Penguin (also known as the Fairy Penguin), which is typically 35 to 40 cm tall and 1 kilogram. Generally larger penguins retain heat better and thus inhabit colder regions, while smaller penguins are found in temperate or even tropical climates.
Penguins emerged in the Eocene era 40 million years ago. Birds like Palaeeudyptes from the Eocene, Pachydyptes from the Miocene and the now extinct Great Auks resembled modern penguins. The links between other bird orders and penguins are still unknown. A distant relationship between penguins and petrels is assumed, but not proved. Most fossil penguins known were large, but not larger than the modern Emperor Penguin. All lived in the southern hemisphere.
Penguins are superbly adapted to an aquatic life. Their wings have become flippers, useless for flight in the air; in the water, however, penguins are astonishingly agile. Within the smooth plumage a layer of air is preserved, ensuring buoyancy. This is the reason a chain of air bubbles stretches behind a diving penguin. The air layer also helps insulate the bird in the icy waters of the Antarctic. The plumage of penguins in tropical and temperate zones is much thinner.
On land, they use their tails and wings to maintain balance.
All penguins have a white underside and a dark (mostly black) upperside. This is for camouflage. A predator looking up from below (such as a Killer Whale or a Leopard Seal) has difficulty distinguishing between a white penguin belly and the reflective water surface.
Diving penguins reach 6 to 12 km/h, though there are reports of velocities of 27 km/h (which are probably realistic in the case of precipitate flight). The small penguins do not usually dive deep, their prey is caught near the surface, and most dives are only one or two minutes in duration. They can dive deep in case of need, however: the large Emperor Penguin has been recorded reaching a depth of 267 metres and staying down for 18 minutes.
On land, penguins are clumsy. They either waddle on their feet or slide on their belly across the snow. However, they can actually run as fast or faster than most humans. They slide on their stomachs, called "tobogganing", to conserve energy and move relatively fast at the same time.
Penguins have an excellent sense of hearing. Their eyes are adapted for underwater vision, and are their primary means of locating prey and avoiding predators; in air, conversely, they are nearsighted. Their sense of smell has not been researched so far.