The Adélie penguin (Pygoscelis adeliae) is a species of penguin common along the entire coast of the Antarctic continent. It is the most widespread penguin species in the Antarctic, and, along with the emperor penguin, is the most southerly distributed of all penguins. It is named after Adélie Land, in turn, named for Adèle Dumont d'Urville, who was married to French explorer Jules Dumont d'Urville, who first discovered this penguin in 1840. Adélie penguins obtain their food by both predation and foraging, with a diet of mainly krill and fish.
Taxonomy and systematics
The first Adélie penguin specimens were collected by crew members of French explorer Jules Dumont d'Urville on his expedition to Antarctica in the late 1830s and early 1840s. Jacques Bernard Hombron and Honoré Jacquinot, two French surgeons who doubled as naturalists on the journey, described the bird for science in 1841, giving it the scientific name Catarrhactes adeliæ. They used specimens collected from an area of the continent which had been named "", French for Adélie Land, itself named for Dumont d'Urville's wife, Adèle. The bird was later placed in several other genera, including Eudyptes, Pygoscelis and the now-defunct genus Dasyrhamphus, and was also later inadvertently redescribed as Pygoscelis brevirostris.
The Adélie penguin is one of three species now assigned to the genus Pygoscelis. DNA evidence suggests the Pygoscelis lineage diverged from that of other penguin species some 38 million years ago, roughly 2 million years after the ancestors of the genus Aptenodytes diverged. Adélie penguins evolved about 19 million years ago, branching from the ancestor of the other two members of the genus (chinstrap and gentoo penguins), both of which evolved some 5 million years later.
Although it has no identifiable subspecies, the Adélie penguin has two distinct genetic lineages: one found primarily in the Ross Sea, and the other widespread throughout the Antarctic.
Etymology
The genus name Pygoscelis is a compound word, composed of the Ancient Greek words , meaning "rump", and skelos, meaning "leg". The members of this genus are often called "brush-tailed penguins", a reference to their long, stiff tail feathers. The birds regularly use their tails for support, and the stiff feathers sweep the ground as the penguins walk. The specific name adeliae indicates the location from which the type specimen was collected.
Distribution and habitat
The Adélie penguin is one of only four penguin species to nest on the continent itself. Breeding colonies are scattered along Antarctica's coasts and on a number of sub-Antarctic islands, including those in the South Orkneys, the South Shetlands, the South Sandwich Islands, the Balleny Islands, Scott Island and South Georgia. The penguins are much less common north of the 60th parallel south but have occurred as vagrants in Australia, New Zealand and southern South America.
During the breeding season, they need bare, rocky ground on which to build their nests. They will not nest on ice, and preferentially choose areas where wind or the angle of the sun (or both) helps to keep snow drifts from accumulating. At the start of the breeding seasons, colony sites may be up to from open water, though the distance decreases as summer progresses and the pack ice breaks up. Once they have finished breeding, adult Adélie penguins typically move to ice floes or ice shelves to moult, though some remain onshore.
During the winter, the birds remain in the pack ice zone, with most moving north to reach areas where there is visible light for at least part of the day – thus north of roughly 73°S. While some remain near their breeding colonies, others may move hundreds or thousands of kilometres away. As long as there are breaks in the pack ice, they can survive hundreds of kilometres south of open water, and birds are known to forage in winter in areas with up to 80% pack ice cover.
Description
thumb|Adult with chicks
The Adélie penguin is a mid-sized bird, measuring in length and weighing . Although the sexes look the same, females have shorter wings and beaks and weigh significantly less. The adult is black on the head, throat and upper parts, with snowy white underparts. It has a conspicuous white around a black iris. The beak is largely covered with black feathers, leaving only the tip exposed; this is primarily black, though it can show indistinct reddish-brown markings. The upper surface of the wing is black with a white trailing edge, while the underside is white with a narrow black leading edge and a small black tip. The legs and feet, which are mostly unfeathered, are pinkish.
Upon hatching, the chick is fully covered in down feathers. This coat of feathers is typically silvery-grey (darker on the head), though some birds are much darker overall. Within 10 days, the chick moults into another set of down feathers, this time all dark smoky-grey. Once they have moulted a third time, 7–9 weeks after hatching, the immature birds are similar to adults in appearance, though they tend to be smaller with a bluer tinge to their upperparts and white (rather than black) chins and throats. They lack the full white eye ring of the adult until they are at least a year old.
Similar species
The adult Adélie penguin is unlikely to be confused with any other species, but the white-throated immature bird can resemble the chinstrap penguin. However, the black on its face extends below its eyes, and it lacks a black line under the throat (the "chinstrap") that the chinstrap penguin has. In addition, the bill of the chinstrap penguin is longer, and lacks the feathering that covers most of the bill of the Adélie penguin. Along with the chinstrap penguins, gentoo penguins are fairly similar to the Adélie due to their Antarctic habitat, as well as their mainly krill and fish centered diet.
Behaviour and ecology
thumb|right|[[Cape Adare]]
thumb|right|In Antarctica
Apsley Cherry-Garrard, a survivor of Robert Falcon Scott's ill-fated British Antarctic Expedition of 1910, documented details of penguin behaviour in his book The Worst Journey in the World. "They are extraordinarily like children, these little people of the Antarctic world, either like children or like old men, full of their own importance..." George Murray Levick, a Royal Navy surgeon-lieutenant and scientist who also accompanied Scott, commented on displays of selfishness among the penguins during his surveying in the Antarctic: "At the place where they most often went in [the water], a long terrace of ice about six feet in height ran for some hundreds of yards along the edge of the water, and here, just as on the sea-ice, crowds would stand near the brink. When they had succeeded in pushing one of their number over, all would crane their necks over the edge, and when they saw the pioneer safe in the water, the rest followed." Levick also detailed the mating habits of Adélie penguins.
One writer observed how the penguin's curiosity could also endanger them, which Scott found a particular nuisance:
thumb|right|Chicks in Antarctica, with [[MV Explorer (1969)|MS Explorer|alt=Chicks in Antarctica, with MS Explorer and icebergs in the background]]
Others on the mission to the South Pole were more receptive to this element of the Adélies' curiosity. Cherry-Garrard writes:
Cherry-Garrard held the birds in great regard. "Whatever a penguin does has individuality, and he lays bare his whole life for all to see. He cannot fly away. And because he is quaint in all that he does, but still more because he is fighting against bigger odds than any other bird, and fighting always with the most gallant pluck, he comes to be considered as something apart from the ordinary bird..."
Despite their size, Adélie penguins are known for their bold and boisterous personality and will challenge other animals, including predators far larger than them. In footage shot for the 2018 BBC Earth documentary Spy in the Snow, the boisterous behaviour of Adélie penguins was made especially apparent when an individual arrived to defend a group of emperor penguin chicks that were being menaced by a southern giant petrel (Macronectes giganteus). Despite the species difference between the Adélie and the emperors, the individual charged the petrel, then placed itself between the predator and the chicks until it retreated.
Adélie penguins usually swim at around . They are able to leap some out of the water to land on rocks or ice.
Food and feeding
The Adélie penguin is known to feed mainly on Antarctic krill, ice krill, Antarctic silverfish, lanternfish (specifically, the Antarctic lanternfish), amphipods (Themisto gaudichaudii, Cyllopus lucassi, Hyperia and unidentified gammariids), sea krill, glacial squid and other cephalopods
Jellyfish including species in the genera Chrysaora and Cyanea were found to be actively sought-out food items, while they previously had been thought to be only accidentally ingested. Similar preferences were found in the little penguin, yellow-eyed penguin and Magellanic penguin.
Breeding
thumb|An egg in the [[Muséum de Toulouse]]
left|thumb|Mating in [[Antarctica]]
thumb|With young chicks
thumb|With a rock for nest construction
Adélie penguins breed from October to February. Adélies build rough nests of stones. Two eggs are laid; these are incubated for 32 to 34 days by the parents taking turns (shifts typically last for 12 days). The chicks remain in the nest for 22 days before joining crèches. The chicks moult into their juvenile plumage and go out to sea after 50 to 60 days.
Adélie penguins arrive at their breeding grounds in late October or November, after completing a migration that takes them away from the Antarctic continent for the dark, cold winter months. Their nests consist of stones piled together. In December, the warmest month in Antarctica (ranging from about to ), the parents take turns incubating the egg; one goes to feed and the other stays to warm the egg. The parent that is incubating does not eat and does not even leave to defecate but instead projects faeces away from the nest. In March, the adults and their young return to the sea. The Adélie penguin lives on sea ice but needs ice-free land to breed. With a reduction in sea ice, populations of the Adélie penguin have dropped by 65% over the past 25 years in the Antarctic Peninsula.