Penguin - biology.

Penguin - biology. I INTRODUCTION Penguin, common name for 17 species of flightless seabirds widely distributed in cooler waters and along coastlines in the Southern Hemisphere. Skilled swimmers, penguins have streamlined, barrel-like bodies that reduce drag in the water. Their wings, modified to form thin, stiff flippers, provide propulsion while swimming. Unlike the bones of other birds, penguin bones are solid, not hollow, which helps them remain submerged underwater. On land penguins have a waddling gait due to their short, thick legs set far back on the body. Penguins come ashore to breed, but they are, in fact, true marine animals, spending as much as 80 percent of their lives at sea. II RANGE AND HABITAT Although penguins are generally associated with extremely cold climates, only two species--the Adélie penguin (Pygoscelis adeliae) and the emperor penguin (Aptenodytes forsteri)--live on the frozen Antarctic continent. Most penguin species live in subantarctic regions (around and just north of the Antarctic Circle) or temperate regions farther north. The greatest variety of penguin species occurs in southern New Zealand, which is home to seven species, and the Falkland Islands, home to five species. Penguin populations are largest on the coast of the Antarctic Peninsula (the northernmost tip of Antarctica) and on subantarctic islands. One small species, the Galápagos penguin (Spheniscus mendiculus), lives on the Galápagos Islands just south of the equator, and several penguin species inhabit the hot, desert coastlines of South America and southern Africa. The birds living in these warmer regions rely on cold and nutrient-rich water currents to survive. III PHYSICAL CHARACTERISTICS Penguins vary in size from the little penguin (Eudyptula minor), which weighs 1.1 kg (2.4 lb) and is about 40 cm (16 in) tall, to the emperor penguin, which grows to 30 kg (66 lb) in weight and stands about 115 cm (45 in) tall. The emperor penguin is small compared to the fossil penguin Anthropornis, which lived 37 million to 45 million years ago on Seymour Island near Antarctica. Fossil records indicate that Anthropornis was around 170 cm (66 in) in height. All penguins have a black back and head and a white breast, but individual species can be distinguished by certain physical characteristics. For instance, the birds in the genus Eudyptes are commonly known as crested penguins for the tuft of bright yellow plumage on their head. Adélie penguins have white, spectacle-like rings around their eyes. Other penguins can be distinguished by bare, pink skin on the head and neck, or varied black and white breast bands. Penguin bills can be black or red, ranging in shape from short and stout to long and curved. Penguin feet are webbed with three toes. Male and female penguins are similar in appearance, although males usually weigh more than females and there are small differences in bill size between the sexes. Penguins are well adapted to cold weather. Their short, stiff feathers form a dense waterproof coat that prevents excess heat loss. Some species have a thick layer of blubber under their skin, but this fat layer mainly acts as a food reserve and contributes little to insulation. IV LIFE OF PENGUINS Penguins spend most of their lives in water and they are excellent swimmers. They travel long distances underwater, propelling themselves with their flipper-like wings and using their webbed feet as rudders. They commonly leap out of the water--a movement known as porpoising--to breathe. On land penguins hop or waddle awkwardly, and in icy or snow areas they can toboggan on their stomachs, paddling themselves forward with their wings. All penguins eat only when they are in the water, catching fish, squid, and crustaceans. Penguins search for food while swimming near the water's surface and then swiftly dive to pursue their prey. Recently scientists have learned more about the diving behavior of penguins by attaching special miniaturized computers to the backs of the birds. These devices record various activities of penguins, providing data on the number and depth of dives made, swimming speeds, and even how often a bird catches and swallows prey. Early results from these studies indicate that penguins are champion divers. The large emperor penguin can reach depths of over 500 m (1,600 ft). A gentoo penguin (Pygoscelis papua) was recorded making over 450 successive dives in 15 hours, at times reaching depths of 160 m (525 ft). A Courting, Nesting, and Egg-Laying Penguins go through courtship, mating, nesting, and the incubation period (warming and hatching of eggs) on land. During this time, which can last over 100 days in some species, many penguins do not return to the sea to feed, and some species, such as male Adélie penguins, can lose up to 30 percent of their body mass. Most penguin species nest in colonies that range from less than 100 pairs to several hundred thousand pairs at a single site. In these colonies the birds live very closely together, with up to three penguin pairs per square meter. The Fiordland penguin (Eudyptes pachyrhynchus) and yellow-eyed penguin (Megadyptes antipodes) are exceptions, breeding as solitary pairs. Some penguins, such as the crested penguins, only visit a colony during breeding or to molt (shed feathers), typically during the Southern Hemisphere summer between October and March. They spend the rest of the year at sea often a long way from land. The gentoo penguin does not migrate long distances and instead stays near its breeding colony throughout the year, feeding in inshore waters. The emperor penguin is unusual in that it returns to its breeding colony on the ice of the Antarctic continent between March and April, at the end of the Southern Hemisphere summer. It then proceeds to lay and incubate its egg and rear the chick during the Antarctic winter in temperatures as low as -62°C (-80°F). Crowded penguin breeding colonies enable penguins to experience social stimulation and interaction. Penguins use a varied and complex range of postural displays and calls in the process of obtaining and defending a nest site and in finding a mate. The gentoo penguin raises and lowers its flippers and calls or bows to its mate, sometimes using its bill to deliver a stone as a gift. The jackass penguin (Spheniscus demersus) throws its head back and gives a loud jackass-like braying call; and the king penguin (Aptenodytes patagonicus) stretches its neck skyward and sings a duet of long calls with its partner. Penguin pairs may remain together for many years, and they often return to the same breeding site year after year. Penguins typically nest on ground surfaces in open habitats, and their nests consist of a simple hollow among boulders or tussock grass, lined with a few stones or bits of vegetation. Some penguins, such as the chinstrap (Pygoscelis antarctica) and gentoo, construct a substantial platform of small stones to support a small nest cup. The little penguin, the Humboldt penguin (Spheniscus humboltdi), and the Magellanic penguin (Spheniscus magellanicus) dig nesting burrows underground up to 1 m (3 ft) in length, but they will also nest under bushes or in caves and crevices among rocks. The king and emperor penguins do not build nests; instead a bird incubates the egg by resting it on top of the feet, covering it with the lower part of the belly. Most penguin species lay two similar-sized white or green eggs at one time, although the king and emperor penguins lay a single large egg. The crested penguins are unique among all birds in laying two eggs of very different sizes--the first egg laid is often less than half the size of the second, and it is the chick from the second egg that is most likely to survive. Scientists do not understand why crested penguins lay two eggs and why the chick from the first egg rarely survives. B Parents and Offspring Once female penguins lay their eggs, both the parents incubate the eggs. The incubation period varies according to species, ranging from 33 days for the little penguin to about 63 days for the emperor penguin. In most medium-sized penguins incubation takes 35 to 38 days. The incubation routine is highly variable among penguin species, although in general both sexes participate in incubation and feeding of young. Male and female Adélie penguins take turns incubating their eggs. The male usually incubates the eggs for the first two weeks, while the female returns to the sea to feed before coming back to take over incubation duties for the next 12 days. When the female takes a turn at incubation the male goes to sea to feed but returns to complete the last incubation shift of 8 days before the chicks hatch. The male emperor penguin incubates for the entire 62 to 64 day period. Not all species undergo such prolonged incubation shifts: in gentoo and Magellanic penguins, incubation typically involves daily changeovers between the male and female, each bird incubating for 24-hour shifts. Chicks hatch with only a thin covering of downy feathers, and they are unable to regulate their own body temperatures or feed themselves. Parents feed their young by regurgitating partially digested food into the chicks' mouths. Chicks remain in the nest, entirely dependent on their parents for food, warmth, and protection for up to several weeks after hatching. This "guard" period lasts only 15 days in the little penguin, but 40 to 50 days in the king and emperor penguins. During this time parents sit on their chicks or partially cover them to transfer their own heat to the chicks in a practice known as brooding. Parents alternate brooding with trips to the sea to obtain food for the chicks. In Adélie, chinstrap, and gentoo penguins, parents share brooding duties equally with changeovers every one to two days. The males in the crested penguins and the females in the emperor penguins perform all brooding duties. In most medium-sized penguins, both parents start feeding at sea around 20 to 30 days after the chicks hatch. The chicks are left in the colony to form loose groups called crèches. Both parents continue to return daily or every few days to feed the chicks. When a parent arrives on shore, it calls its chicks and waits for an answering call from the offspring. Parents and chicks can recognize each other's calls, enabling each parent to locate and feed its own chick even in colonies numbering thousands of birds. In some cases a "feeding chase" ensues in which one or both chicks leave the crèche and chase after the food-laden parent. The parent eventually ends the chase by stopping and regurgitating partially digested food for the chicks. Toward the end of the crèche phase, which lasts around 20 to 30 days, young penguins shed their down and acquire their first full plumage prior to entering the sea to fend for themselves. In several species, young birds in their first or second year will return to the same colony to breed. Macaroni and king penguins may delay breeding until they are five to eight years of age. Penguins may live from 15 to 20 years. Once chicks depart the breeding colony, most adults go to sea to feed and fatten up before returning to the colony for molting. While most birds shed their feathers and grow new ones during a relatively long period of the year, penguins renew their entire plumage over two to four weeks. A molting penguin generally stands immobile during its molting period, and has a very swollen, disheveled appearance. During molting penguins do not enter the water to feed and may lose up to 50 percent of their body mass. V CONSERVATION STATUS The populations of many penguin species remain abundant. Exceptions include the erect-crested, yellow-eyed, and Galápagos penguins, all of which are listed as endangered on the Red List of Threatened Species of the World Conservation Union (IUCN), a nongovernmental organization that compiles global information on endangered plants and animals. Penguins have only a few natural predators. On land, skuas, gulls, and giant petrels feed on penguin eggs and chicks; at sea, leopard seals hunt adult penguins. In some areas penguins nest within the territories of fur seals, and male seals can destroy penguin nests and even kill adult penguins during fights with other males. On Macquarie Island just south of Australia elephant seals can completely demolish the nests and eggs of gentoo penguin colonies just by moving through them. Perhaps due to the remoteness of penguin breeding sites, particularly those on uninhabitable islands, humans do not pose a large direct threat to penguins. In the past, sailors killed hundreds of thousands of penguins, in particular king penguins on Macquarie Island and the Falkland Islands, and used their body parts to create oil for lubricants and fuel. Elsewhere, particularly on previously uninhabited islands such as those in the Galápagos and parts of New Zealand, animals introduced by humans, including dogs, rats, and cats, hunt penguin eggs and chicks or disturb breeding colonies. A number of human-created global problems, such as oil spills, global warming or overfishing, may eventually endanger penguin populations, and these threats require continuing research and monitoring efforts in order to protect these remarkable birds. Scientific classification: Penguins make up the family Spheniscidae in the order Sphenisciformes. Contributed By: Tony D. Williams Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.