Thursday, July 16, 2009

Adelie Penguins Annual Breeding Rituals

Penguin parenting: Adelie penguins reunite for their annual breeding rituals
Animals, July-August, 1997 by Michelle Alten

Near Antarctica's Ross Sea, a bitter wind rips across ice-covered beach. In the blizzard, Adelie penguins hunker 'clown on their nests, covering their newly laid eggs. It is November, and another rigorous breeding season is under way.

Life in Antarctica is a challenge. In the winter, coastal temperatures can drop to minus 22 degrees Fahrenheit; in the summer, they may climb only slightly above freezing. But despite seemingly unbeatable odds, Adelie populations flourish here with a breeding strategy finely tuned to this tempestuous polar region. Adelies are so well adapted to this frigid climate that, while most southern penguins breed in the subantarctic, on outer islands, or on the Antarctic Peninsula, Adelies have colonies all along the Antarctic coast. Emperor penguins also breed in the coldest regions of Antarctica, but Adelies are far more numerous, estimated at 2,465,800 pairs, compared with 195,400 pairs of emperors.

In late October, after a winter on the sea's pack ice, Adelies journey back to their breeding grounds. It is the austral spring, and a frozen sea means Adelies may travel across 60 miles of ice as they return to their colony. First the male arrives, then the female. Each recognizes its mate's call and nesting site from previous years, and perhaps even its partner's physical features. Unless one of the mates fails to return, a pair may reunite for many consecutive breeding seasons.

After a long winter apart, the two penguins thrust their beaks in the air, wave their heads, and let out a raucous call. After this display and renewed bonding, the birds ramble along the barren shore, gathering pebbles in their beaks. Then they strut back to the rookery and place them gingerly around their stone nests.

With the breeding season under way, the penguin colony is alive with activity. At the edge of the rookery, young males, three and four years old, stretch their bills toward the sky and cry out as they stake out their territory and attempt to attract a mate.

The female Adelie penguin lays two eggs. The male, in charge of the first stint of incubation, steps over the eggs and tucks them beneath two protective flaps of skin on his belly. These brood patches keep the eggs secure and warm. The female, free to feed, scampers through the colony down to the beach, pads over a stretch of ice, then disappears into the sea.

For the male, incubation is an endurance test. The father-to-be has not eaten since his arrival, and it may be weeks before his partner returns. This extensive fasting period, which may last as long as 40 days, can cause the penguin to lose a third of his weight.

After a boisterous greeting, the female returning from sea steps behind her partner and scoots into position to take over the job of incubation. Relieved of duty, the male toboggans down a snow-covered hillside and slips off to sea to feed on krill, small shrimplike creatures that are the keystone of Antarctica's complex food chain.

"Adelies capitalize on a huge food source by breeding in the Antarctic," explains Frank Todd, founder of Sea World's Penguin Encounter and author of numerous books on penguins. "They eliminate competition with birds that nest farther north, and even though emperors, which also nest in the Antarctic, include krill in their diet, they also feed extensively on fish and squid."

Penguins must keep careful watch over their eggs. At the rookery's edge, a sheathbill, a white scavenger with a fleshy pink wattle, pushes a penguin egg from its nest. Repeatedly the bird retreats, approaches, and pecks at the shell. Finally it shatters a hole in the egg and begins to eat. Other sheathbills gather for a share, until one flies off with the egg in its beak. Nearby, skuas, black gull-like birds, hover, also hoping to snatch an unguarded egg.

After about 36 days, the faint peeping of a newly hatched chick is heard amid the chatter of adult penguins. The charcoal chick taps at its shell with its egg tooth, gradually poking a way out. After a time, the hungry chick pecks at the parent's bill, begging for food. The adult reaches down, opens its beak, and regurgitates a meal of krill into the tiny, gaping bill.

While the chicks are being reared, pack ice can present a survival challenge, forcing the birds to walk rather than swim to the sea. While Adelies walk about three miles per hour, they can swim almost twice as fast. "The pack ice reduces the frequency that they can feed their chicks," notes David Ainley, an ornithologist and author of The Breeding Biology of the Adelie Penguin. "As a result, chicks can be smaller in weight. This gives them less of a time cushion in which to learn how to catch their own food."

Around the age of four weeks, Adelie chicks leave their parents' protection and gather to form a creche, a group of up to 100 or more youngsters. The chicks huddle together for warmth and for defense against skuas. Now both parents feed at sea, nourishing themselves and gathering food for their growing youngster.

Gradually the chicks lose their fuzzy down and gain their mature black and white feathers. After 56 days, many leave the creche behind. Now larger in size, they return to their nests, no longer fearing the assaults of skuas.

A cluster of adults forms at the water's edge. A few penguins peer over the ice. No leopard seals. One bird pauses, then dives into the icy ocean. The next one follows, then the next. Finally all the penguins tumble into the sea, like a chain of dominoes. In the water, penguins take no chances with leopard seals, which are ferocious predators. A seal will grab hold of a penguin, whip it inside out, removing its skin, and swallow it whole.

In Antarctica the Adelies face constant hazards. During the austral summer, storms with savage gales and freezing temperatures often rush in without warning. A layer of blubber and tightly packed feathers help adults withstand the cold. Young chicks are often not as lucky. If they are not sheltered by a parent or the creche, they may freeze or be buried in snow.

By February many Adelie juveniles have made it through the breeding season and are ready to fledge. Despite the rigors of Antarctic life, studies in the Ross Sea have shown that about 75 to 85 percent of chicks that hatch usually survive to the fledgling stage.

"The number of Adelie penguins has been increasing in the high-latitude areas of the Ross Sea," Ainley points out. "The changes may be due to decreases in the amount of pack ice, caused by global warming."

Meanwhile, at the close of each breeding season winter steals in, covering the continent with darkness. Antarctica's "ice birds" leave behind their colonies and head out on the frozen sea.
Bibliography for: "Penguin parenting: Adelie penguins reunite for their annual breeding rituals"

Michelle Alten "Penguin parenting: Adelie penguins reunite for their annual breeding rituals". Animals. 16 Jul, 2009.

Image: Flickr Uploaded on January 28, 2007 by mark van de wouw

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