Penguins (order Sphenisciformes, family Spheniscidae) are a group of aquatic, flightless birds living almost exclusively in the Southern Hemisphere. The number of penguin species is debated. Depending on which authority is followed, penguin biodiversity varies between 17 and 20 living species, all in the subfamily Spheniscinae. Some sources consider the White-flippered Penguin a separate Eudyptula species, while others treat it as a subspecies of the Little Penguin; the actual situation seems to be more complicated. Similarly, it is still unclear whether the Royal Penguin is merely a color morph of the Macaroni penguin. Also eligible to be a separate species is the Northern population of Rockhopper penguins. Although all penguin species are native to the southern hemisphere, they are not, contrary to popular belief, 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.
The largest living species is the Emperor Penguin (Aptenodytes forsteri): adults average 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 (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 (see below for more). 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.
Penguins seem to have no special fear of humans and have approached groups of explorers without hesitation. This is probably on account of there being no land predators in Antarctica or the nearby offshore islands that prey on or attack penguins. Instead, penguins are at risk at sea from predators such as the leopard seal. Typically, penguins do not approach closer than about 3 meters (10 ft) at which point they become nervous. This is also the distance that Antarctic tourists are told to keep from penguins (tourists are not supposed to approach closer than 3 meters, but are not expected to withdraw if the penguins come closer).
Penguins are superbly adapted to an aquatic life. Their vestigial 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. The air layer also helps insulate the birds in cold waters. On land, penguins use their tails and wings to maintain balance for their upright stance.
All penguins are countershaded for camouflage – that is, they have a white underside and a dark (mostly black) upperside. 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 which reach a depth of 565 m (1,870 ft) and last 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.
Penguins have a thick layer of insulating feathers which serve to keep them warm in water (heat loss in water is much greater than in air). The Emperor penguin (the largest penguin) has the largest body mass of all penguins, which further reduces relative surface area and heat loss. They also are able to control blood flow to their extremities, reducing the amount of blood which gets cold, but still keeping the extremities from freezing. In the extreme cold of the Antarctic winter, the females are at sea fishing for food leaving the males to brave the weather by themselves. They often huddle together to keep warm and rotate positions to make sure that each penguin gets a turn in the center of the heat pack.
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.
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, though the two largest species, the Emperor and the King Penguins, lay only one. With the exception of the Emperor Penguin in all penguins share the incubation duties. These incubation shifts can last days and even weeks as one member of the pair feeds at sea.
Penguin eggs are smaller than any other bird species when compared proportionally to the weight of the parent birds; at 52 grams, the Little Penguin egg is 4.7% of its mothers' weight, and the 450-gram 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.
Updated after Marples (1962), Acosta Hospitaleche (2004), and Ksepka et al. (2006).
Subfamily Spheniscinae – Modern penguins
The basal penguins lived around the time of the Cretaceous–Tertiary extinction event somewhere in the general area of (southern) New Zealand and Byrd Land, Antarctica. Due to plate tectonics, these areas were at that time less than apart rather than the of today. The most recent common ancestor of penguins and their sister clade can be roughly dated to the Campanian–Maastrichtian boundary, around 70–68 mya. What can be said as certainly as possible in the absence of direct (i.e., fossil) evidence is that by the end of the Cretaceous, the penguin lineage must have been evolutionarily well distinct, though much less so morphologically; it is fairly likely that they were not yet entirely flightless at that time, as flightless birds have generally low resilience to the breakdown of trophic webs which follows the initial phase of mass extinctions because of their below-average dispersal capabilities (see also Flightless Cormorant).
Perudyptes from northern Peru was dated to 42 mya. An unnamed fossil from Argentina proves that by the Bartonian (Middle Eocene), some 39–38 mya, primitive penguins had spread to South America and were in the process of expanding into Atlantic waters.
But size plasticity seems to have been great at this initial stage of penguin radiation: on Seymour Island, Antarctica, for example, around 10 known species of penguins ranging in size from medium to huge apparently coexisted some 35 mya during the Priabonian (Late Eocene). It is not even known whether the gigantic palaeeudyptines constitute a monophyletic lineage, or whether gigantism was evolved independently in a much restricted Palaeeudyptinae and the Anthropornithinae – whether they were considered valid, or whether there was a wide size range present in the Palaeeudyptinae as delimited as usually done these days (i.e., including Anthropornis nordenskjoeldi). The oldest well-described giant penguin, the 5-foot-tall Icadyptes salasi, actually occurred as far north as northern Peru about 36 mya.
In any case, the gigantic penguins had disappeared by the end of the Paleogene, around 25 mya. Their decline and disappearance coincided with the spread of the Squalodontoidea and other primitive, fish-eating toothed whales, which certainly competed with them for food, and were ultimately more successful. A new lineage, the Paraptenodytes which includes smaller but decidedly stout-legged forms, had already arisen in southernmost South America by that time. The early Neogene saw the emergence of yet another morphotype in the same area, the similarly-sized but more gracile Palaeospheniscinae, as well as the radiation which gave rise to the penguin biodiversity of our time.
The genus Aptenodytes appears to be the basalmost divergence among living penguins; they have bright yellow-orange neck, breast, and bill patches; incubate by placing their eggs on their feet, and when they hatch the chicks are almost naked. This genus has a distribution centered on the Antarctic coasts and barely extends to some subantarctic islands today.
Pygoscelis contains species with a fairly simple black-and-white head pattern; their distribution is intermediate, centered on Antarctic coasts but extending somewhat northwards from there. In external morphology, these apparently still resemble the common ancestor of the Spheniscinae, as Aptenodytes' autapomorphies are in most cases fairly pronounced adaptations related to that genus' extreme habitat conditions. As the former genus, Pygoscelis seems to have diverged during the Bartonian, but the range expansion and radiation which led to the present-day diversity probably did not occur until much later; around the Burdigalian stage of the Early Miocene, roughly 20–15 mya.
The genera Spheniscus and Eudyptula contain species with a mostly subantarctic distribution centered on South America; some, however, range quite far northwards. They all lack carotenoid coloration, and the former genus has a conspicuous banded head pattern; they are unique among living penguins by nesting in burrows. This group probably radiated eastwards with the Antarctic Circumpolar Current out of the ancestral range of modern penguins throughout the Chattian (Late Oligocene), starting approximately 28 mya. While the two genera separated during this time, the present-day diversity is the result of a Pliocene radiation, taking place some 4–2 mya.
The Megadyptes–Eudyptes clade occurs at similar latitudes (though not as far north as the Galapagos Penguin), has its highest diversity in the New Zealand region, and represent a westward dispersal. They are characterized by hairy yellow ornamental head feathers; their bills are at least partly red. These two genera diverged apparently in the Middle Miocene (Langhian, roughly 15–14 mya), but again, the living species of Eudyptes are the product of a later radiation, stretching from about the late Tortonian (Late Miocene, 8 mya) to the end of the Pliocene.
The geographical and temporal pattern or spheniscine evolution corresponds closely to two episodes of global cooling documented in the paleoclimatic record. The emergence of the subantarctic lineage at the end of the Bartonian corresponds with the onset of the slow period of cooling that eventually led to the ice ages some 35 million years later. With habitat on the Antarctic coasts declining, by the Priabonian more hospitable conditions for most penguins existed in the subantarctic regions rather than in Antarctica itself. Notably, the cold Antarctic Circumpolar Current also started as a continuous circumpolar flow only around 30 mya, on the one hand forcing the Antarctic cooling, and on the other facilitating the eastward expansion of Spheniscus to South America and eventually beyond.
Later, an interspersed period of slight warming was ended by the Middle Miocene Climate Transition, a sharp drop in global average temperature from 14–12 mya, and similar abrupt cooling events followed at 8 mya and 4 mya; by the end of the Tortonian, the Antarctic ice sheet was already much like today in volume and extent. The emergence of most of today's subantarctic penguin species almost certainly was caused by this sequence of Neogene climate shifts.
What seems clear is that penguins belong to a clade of Neoaves (living birds except paleognaths and fowl) which comprises what is sometimes called \"higher waterbirds\" to distinguish them from the more ancient waterfowl. This group contains such birds as storks, rails, and the seabirds, with the possible exception of the Charadriiformes.
Inside this group, penguin relationships are far less clear. Depending on the analysis and dataset, a close relationship to Ciconiiformes or to Procellariiformes has been suggested. Some think the penguin-like plotopterids (usually considered relatives of anhingas and cormorants) may actually be a sister group of the penguins, and that penguins may have ultimately shared a common ancestor with the Pelecaniformes and consequently would have to be included in that order, or that the plotopterids were not as close to other pelecaniforms as generally assumed, which would necessitate splitting the traditional Pelecaniformes in three.
It is also possible that penguin comes from the Latin pinguis, “fat”. This is supported by the fact that the corresponding words in most other languages (e.g., French pingouin, German Pinguin) have i instead of e as the first vowel. However, a Welsh i is often sound-shifted to an e in the English language.
Another theory states that the word is an alteration of “pen-wing”, with reference to the rudimentary wings of both Great Auks and penguins, but there is no evidence to support this.
What may be a King Penguin but certainly is a member of the Spheniscidae appears on a 1599 map at the Strait of Magellan with the caption "Pinguyn". The map's features are labeled in Latin, such as Fretum Magellanicum ("Strait of Magellan"). In addition, there is ample evidence that the Latin term anser magellanicus ("Goose of Magellan" or "Magellanic Goose") was the usual term for penguins in the scholarly literature of that time. If the English word was derived from Latin – e.g. avis pinguis ("fat bird") or pinguinus ("the fat one") – it must have originated considerably earlier than 1600.
The pronunciation of the word in English varies somewhat: as either "PEN-guin" or "PENG-guin".
Penguins are popular around the world, primarily for their unusually upright, waddling gait and (compared to other birds) lack of fear of humans. Their striking black-and-white plumage is often likened to a tuxedo suit. Mistakenly, some artists and writers have penguins based at the North Pole. This is incorrect, as there are almost no wild penguins in the northern hemisphere, except the small group on the northernmost of the Galápagos.
Penguins have been the subject of many books and films such as Happy Feet and Surf's Up, both CGI films; March of the Penguins, a documentary based on the migration process of Emperors; and a parody entitled Farce of the Penguins. Penguins have also found their way into a number of cartoons and television dramas; perhaps the most notable of these is Pingu, created by Silvio Mazzola in 1986 and covering more than 100 short episodes.
The tendency of penguins to form large groups feeds the stereotype that they all look exactly alike, a popular notion exploited by cartoonists such as Gary Larson.
In the mid-2000s, penguins became one of the most publicized species of animals that form lasting homosexual couples. A children's book, And Tango Makes Three, was written about one such penguin family in the New York Zoo.