The Adélie penguin (Pygoscelis adeliae) is a species of penguin common along the entire coast of the Antarctic continent, which is its only habitat. It is the most widely spread penguin species,[2] as well as the most southerly distributed of all penguins, along with the emperor penguin. 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.[3] Adélie penguins obtain their food by both predation and foraging, with a diet of mainly krill and fish.[2]
Taxonomy
The Adélie penguin is one of three species in the genus Pygoscelis. Mitochondrial and nuclear DNA evidence suggests the genus split from other penguin species around 38 million years ago, about 2 million years after the ancestors of the genus Aptenodytes. In turn, the Adélie penguins split off from the other members of the genus around 19 million years ago.[4]
Description
These penguins are mid-sized, being 46 to 71 cm (18 to 28 in) in height and 3.6 to 6.0 kg (7.9 to 13.2 lb) in weight.[5][6] Distinctive marks are the white ring surrounding the eye and the feathers at the base of the bill. These long feathers hide most of the red bill. The tail is a little longer than other penguins' tails. The appearance looks somewhat like a tuxedo. They are a little smaller than most other penguin species.[7]
Adélie penguins usually swim at around 5 miles per hour (8.0 km/h).[8] They are able to leap some 3 metres (10 ft) out of the water to land on rocks or ice.[9]
Ecology
Diet
The Adélie penguin is known to feed mainly on: Antarctic krill, ice krill, Antarctic silverfish, sea krill and glacial squid (diet varies depending on geographic location) during the chick-rearing season. The stable isotope record of fossil eggshell accumulated in colonies over the last 38,000 years reveals a sudden change from a fish-based diet to krill that began around 200 years ago. This is most likely due to the decline of the Antarctic fur seal since the late 18th century and baleen whales during the early 20th century. The reduction of competition from these predators has resulted in a surplus of krill, which the penguins now exploit as an easier source of food.[10]
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.[11]
Predators
Adult Adélie penguins are regularly preyed upon by leopard seals. South polar skuas, in particular and Giant petrels kill many chicks and eat eggs as well. Giant petrels and orcas will occasionally kill adult Adelie penguins. Kelp gulls and snowy sheathbills also prey on chicks and eggs.[12]
Distribution and habitat
Based on a 2014 satellite analysis of fresh guano-discoloured red/brown coastal areas, 3.79 million breeding pairs of Adélie penguins are in 251 breeding colonies,[13] a 53% increase over a census completed 20 years earlier. The colonies are distributed around the coastline of the Antarctic land and ocean. Colonies have declined on the Antarctic Peninsula since the early 1980s,[14] but those declines have been more than offset by increases in East Antarctica[citation needed]. During the breeding season, they congregate in large breeding colonies, some over a quarter of a million pairs.[15] Individual colonies can vary dramatically in size, and some may be particularly vulnerable to climate fluctuations.[16] The Danger Islands have been identified as an "important bird area" by BirdLife International largely because it supports Adélie penguin colonies,[17] with 751,527 pairs recorded in at least five distinct colonies. In March 2018, a colony of 1.5 million was discovered.[18][19]
Adélie penguins breed from October to February on shores around the Antarctic continent. 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.
Behaviour
Apsley Cherry-Garrard was a survivor of Robert Falcon Scott's ill-fated British Antarctic Expedition of 1910, and he 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."[20] 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."[21]
One writer observed how the penguin's curiosity could also endanger them, which Scott found a particular nuisance:
The great trouble with [the dog teams] has been due to the fatuous conduct of the penguins. Groups of these have been constantly leaping onto our [ice] floe. From the moment of landing on their feet their whole attitude expressed devouring curiosity and a pig-headed disregard for their own safety. They waddle forward, poking their heads to and fro in their usually absurd way, in spite of a string of howling dogs straining to get at them. "Hulloa!" they seem to say, "here’s a game – what do all you ridiculous things want?" And they come a few steps nearer. The dogs make a rush as far as their harness or leashes allow. The penguins are not daunted in the least, but their ruffs go up and they squawk with semblance of anger.… Then the final fatal steps forward are taken and they come within reach. There is a spring, a squawk, a horrid red patch on the snow, and the incident is closed.[22]
Others on the mission to the South Pole were more receptive of this element of the Adélies' curiosity. Cherry-Garrard writes:
Meares and Dimitri exercised the dog-teams out upon the larger floes when we were held up for any length of time. One day, a team was tethered by the side of the ship, and a penguin sighted them and hurried from afar off. The dogs became frantic with excitement as he neared them: he supposed it was a greeting, and the louder they barked and the more they strained at their ropes, the faster he bustled to meet them. He was extremely angry with a man who went and saved him from a very sudden end, clinging to his trousers with his beak, and furiously beating his shins with his flippers.… It was not an uncommon sight to see a little Adélie penguin standing within a few inches of the nose of a dog which was almost frantic with desire and passion.[23]
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."[24]
Despite their size, Adélie penguins are known for their bold and boisterous personality, and will challenge other animals, including predators far larger than them.[25] 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 chase off a Southern giant petrel (Macronectes giganteus) that had landed to threaten a group of emperor penguin chicks, in spite of the species difference between them.[26]
Reproduction
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 (about −2 °C or 28 °F/-19°C or -2.2°F), 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 doesn't even leave to defecate but instead projects feces away from the nest.[27] In March, the adults and their young return to the sea. The Adélie penguin lives on sea ice, but needs the 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.[14]
Young Adélie penguins which have no experience in social interaction may react to false cues when the penguins gather to breed. They may, for instance, attempt to mate with other males, with young chicks or with dead females. The first to record such behavior was Dr. George Murray Levick, in 1911 and 1912, but his notes were deemed too indecent for publication at the time; they were rediscovered and published in 2012.[28][n 1]"The pamphlet, declined for publication with the official Scott expedition reports, commented on the frequency of sexual activity, auto-erotic behaviour and seemingly aberrant behaviour of young unpaired males and females, including necrophilia, sexual coercion, sexual and physical abuse of chicks and homosexual behaviour," states the analysis written by Douglas Russell and colleagues William Sladen and David Ainley. "His observations were, however, accurate, valid and, with the benefit of hindsight, deserving of publication."[29][30] Levick observed the Adélie penguins at Cape Adare, the site of the largest Adélie penguin rookery in the world.[31] As of June 2012, he has been the only one to study this particular colony and he observed it for an entire breeding cycle.[30] The discovery significantly illuminates the behaviour of the species whose population some researchers[32] believe to be a bellwether of climate change.[30]
Migration
Adélie penguins living in the Ross Sea region in Antarctica migrate an average of about 13,000 kilometres (8,100 mi) each year as they follow the sun from their breeding colonies to winter foraging grounds and back again. During the winter, the sun does not rise south of the Antarctic Circle, but sea ice grows during the winter months and increases for hundreds of miles from the shoreline, and into more northern latitudes, all around Antarctica. As long as the penguins live at the edge of the fast ice, they will see sunlight. As the ice recedes in the spring, the penguins remain on the edge of it, until once again, they are on the shoreline during a sunnier season. The longest treks have been recorded at 17,600 kilometres (10,900 mi).[34]
Osmoregulation
Adélie penguins are faced with extreme osmotic conditions, as their frozen habitats offer little fresh water. Such desert conditions mean that the vast majority of the available water is highly saline, causing the diets of Adélie penguins to be heavy in salt.[35] They manage to circumvent this problem by eating krill with internal concentrations of salt at the lower end of their possible concentrations, helping to lower the amount of ingested salts.[35] The amount of sodium imposed by this sort of diet is still relatively heavy and can create complications when considering the less tolerant chicks. Adult Adélie penguins feed their chicks by regurgitating the predigested krill, which can impose an excessive salt intake on the chicks. Adult birds address this problem by altering the ion concentrations while the food is still being held in their stomachs. By removing a portion of the sodium and potassium ions, adult Adélie penguins protect their chicks from ingesting excessive amounts of sodium.[35] Adélie penguins also manage their salt intake by concentrating cloacal fluids to a much higher degree than most other birds are capable. This ability is present regardless of ontogeny in Adélie penguins, meaning that both adults and juveniles are capable of extreme levels of salt ion concentration.[35] However, chicks do possess a greater ability to concentrate chloride ions in their cloacal fluids.[35] Salt glands also play a major role in the excretion of excess salts. In aquatic birds such as the Adelie penguin, nasal salt glands excrete an extremely concentrated sodium chloride solution, reducing the load on their kidneys.[36]
These excretions are crucial in the maintenance of Antarctic ecosystems. Penguin rookeries can be home to thousands of penguins, all of which are concentrating waste products in their digestive tracts and nasal glands.[37] These excretions inevitably drop to the ground. The concentration of salts and nitrogenous wastes helps to facilitate the flow of material from the sea to the land, serving to make it habitable for bacteria which live in the soils.[37]
Pygoscelis adeliae
Distribution of the Adélie penguin
Nesting sites in red
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