There are 3 penguins in the Pygoscelis Genus and DNA evidence suggests that the genus split off from other penguins around 38 million years ago and the Adelie's split from the Chinstraps and the Gentoo penguins about 19 million years ago. In 1830 the French explorer Jules Dumont d'Urville named them for his wife, along with Adelie Land.
The popular image of a penguin with a glistening white front, dapper black head, back and wings with the expressive white eye ring, the Adelie Penguin is the most widely distributed, but not the most numerous of the Antarctic penguins. Weighing 3.8 to 6.8 kg (8.3 -15 lbs)
Adelie Penguins are social birds and nest and feed in groups. Colonies can contains thousands of nests packed close together and the birds leave for the sea and return in groups. This acts as protection from their main predator, Leopard Seals. These large seals patrol the waters off a penguin colony and entering the water in a group reduces the chance of a penguin being singled out as dinner. On land skuas can present a risk to unattended eggs or chicks and the birds will work in pairs to provoke brooding penguins into leaving their nests so that a chick or egg can be stolen.
Studies on fossilised eggshells from sites where Adelies have been for a long time reveal that 200 years ago there was a sudden change in diet from fish to krill, this is thought to coincide with the commercial harvesting of Antarctic Fur seals and later of the baleen whales, so leaving more krill for the penguins to eat. The[y still eat not only krill but some fish and squid.
Ninety percent of an Adelie Penguins life is spent at sea where it can dive for up to 5 minutes and to a depth of 500ft. Although they don't usually dive this deep.
During the summer breeding season Adelie Penguins are common along all the Antarctic coasts with land and some sub antarctic islands. The Adelie nests further south than any other penguin with its nesting colony at Cape Royds (77°33'S 166°9'E)being the furthest south until, in the mid 1980's they recolonised Cape Barne (77°35'S 166°9'E And as far north as Zavodovski Island in the South Sandwich Islands (56°20'S 27°35'W)
During the winter months the Adelie Penguins feed and rest in the pack ice surrounding Antarctica's land fast ice, in the Austral spring, October or November the males arrive at their breeding grounds and occupy their simple nest of stones from the previous year. Soon the females arrive. They usually seek out their partner from the previous year, if he has survived the winter and courting begins. There is always a lot of noise and excitement about theft of stones from each others nests and stones are often presented proudly as courting gifts.
The stones are so important that some female Adelie Penguins appear to be involved in prostitution, having sex in exchange for stones. Researchers from the University of Otago in New Zealand were surprised to see females removing stones from other nests and on several occasions they witnessed the female mating with a male who wasn't her partner and afterwards returning to her nest with a stone from his nest. A good stone nest is important because in the event of a warm spell it can keep the eggs out of the puddles and guano which might either chill the eggs or suffocate the embryo. By carbon dating solidified stomach contents, peat moss deposits and bone and feather samples from various moulting sites, researchers have shown that Adelie penguins have returned to the same nest sites for a staggering 44,000 years.
The eggs are laid in December and parents take it in turns to incubated the two eggs. Initially one parent remains with the chicks to warm and protect them but as they grow and require more food, both parents forage. When the chicks are nearly full grown the return of an adult bird to the colony prompts a mobbing and the bird runs, fast, until it has shaken off all but the most persistent chicks which it then feeds, as there is a good chance that they have recognised their parent and stayed the course. As February turns into March the chicks are fledged, their back feathers are a very dark grey and the white on their fronts comes higher up under their chins than it will when they are mature. Adults and juvenile birds leave the nesting beaches and head out into the pack ice.
In the SCAR (Scientific Committee on Antarctic Research) report of 1993 the populations in all areas were described as increasing but the recent report by the University of Michigan http://sitemaker.umich.edu/section3group1/results_and_discussion uses data collected up until 2006 to show that the severe decline in the population of Adelie penguins can be linked to the decline in sea ice extent, that then impacts on the food resources, algae and krill, of the Adelie penguins.
Text © B & C Alexander