General Information about Penguins
Penguins are flightless birds (Class - Aves). As other birds they have feathers, lay eggs and have forelimbs modified as wings (in the penguins' case stiff flippers for swimming). They are also warm-blooded (around 40 degree C) and have a reduced reproductive system (one functional ovary or testis) similar to other birds. Their Order is Sphenisciformes and the Family is Spheniscidae which includes all penguins living and extinct.
Fossil Records
Scientists recognize 35 species of extinct penguins. Penguins probably evolved from flying birds more than 40 million years ago. The first penguin fossils were found in New Zealand in the mid-1800's. One fossil penguin, Palaeeudyptes antarcticus lived in the Eocene Period (38 to 42 million years ago). It was estimated to be 4-5 feet tall. Fossil records showed that largest penguins lived in the Miocene Period (11 to 25 million years ago). Pachydyptes ponderous probably stood 4.5 to 5 feet and weighed 198 to 298 pounds, and the Anthropomis nordenskjoldi probably stood 5 to 5.9 feet and weighed 198 to 298 pounds.
In the fall of 2008, researchers discovered a previously unknown New Zealand species, the Waitaha penguin that was hunted to extinction by 1500.The extinction of the Waitaha penguin allowed the yellow-eyed penguin to thrive.
Recently (2010) paleontologists have unearthed in Peru the first extinct penguin with preserved evidence of scales and feathers.The 36 million year old fossil shows the new giant penguin's feathers were reddish brown and gray. The new species, Inkayacu paracasensis, or Water King was nearly 5 feet tall and weighed between 119 and 132 pounds. It lived in a period when the planet was very warm, totally unlike today's penguins.
The Water King penguin had feathers with broad shafts similar to living penguins which aid streamlining the body. Bird feathers get their some of their coloration from the size and arrangements of nanoscale structures called melanosomes. Melanosomes in Inkayacacu were similar to those in birds, but not to living penguins. Why? The Eocene seas were a different kind of place. There were no seals. The living penguin's feathers are black, so perhaps the change of feather coloration is related to the primary penguin predators. However, the odd arrangement of melanosomes in the living penguin feathers may br due to the need for increased structural support. Since the wide, tight packed melanosomes make feathers resistant to breaking, some authors feel the change in melanosomes might have been driven by the pressure of flying underwater. See artist's rendition of how this penguin might have looked.
The reasons for most penguins' extinction is not clear. Some scientists hypothesize that seals, whales and penguins may have competed for the same food source, and that the penguins may have become prey themselves. The closet living relatives to penguins are in the order Procellariiformes (the albatrosses, shearwaters and petrels)
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Physical Characteristics
The penguin body is fusiform and streamlined, adapted for swimming. The tail is short and wedge-shaped. The legs and webbed feet are set far back on the body, which causes penguins to walk upright on land and also to aid in streamlining and steering while swimming. All adult penguins are counter shaded: that is they are dark on their dorsal (back) surfaces and white on their ventral (underside) surfaces. Their wings are modified into paddle like flippers. The bones are much flattened, solid, dense, broadened, with the joint of the elbow and wrist essentially fused. This forms a rigid, tapered flat flipper for swimming. Their cruising speed speed in water is about 6 miles per hour. Each flipper is covered with short, scale-like feathers. Penguins have bills to capture fish, squid and crustaceans. The bills tend to be long and thin is species that are primarily fish eaters, and shorter and stouter in those that mainly feed on krill. The mouth is lined with horny, rear-directed spines to aid in swallowing live prey. Penguin legs are short, strong and have knees. Feet are webbed, with visible claws. The legs are set far back on the body to aid streamlining and steering, while swimming. Penguins walk with short hops or steps, sometimes using their bills or tails to assist them on steep climbs. Antarctic species can move much faster over ice by tobogganing on their bellies, using their flippers and feet to help them move along. The tail is short and wedge shaped with 14 to 18 stiff tail feathers. The Pygoscelis genus has longer tail feathers, which they often use as a prop when on land. Males are generally larger than females.
Feathers
Shiny feathers uniformly overlap to cover the penguin's skin. They are highly specialized-short broad and closely spaced, the outer part of the feather is waterproof, helping to keep water away from the skin. The inner down section traps an insulating layer of air, keeping the penguin warm when in freezing water. Penguins have more feathers than most other birds, with about 70 feathers per square inch. Penguins generally have trouble staying cool when out of water. Penguins often hold out their flippers to radiate heat and make their feathers stand up to flush some of the warm air trapped within. Some species have bare skin on their face with which to radiate heat, while others nest underground or in the forest. Most penguins go through one complete molt (shed their feathers) annually generally after the breeding season. Molting is an essential function as feathers wear out. Feathers become worn when penguins rub against each other, come in contact with the ground and water, and regularly preen (clean, rearrange and oil) their feathers. New feathers grow under the old ones pushing them out. During the molt penguins stay out of the water as their feathers lose some insulating and waterproofing capabilities. They therefore have to fast, so before their molt they build a fat layer, that provides energy until the molt is over.
Longevity and predators
The average penguin lives 15 to 20 years, some considerably longer. There is a high mortality especially among the young. With the crested penguin the smaller egg or chick characteristically has a high mortality. When in the water penguins main predators are leopard seals, fur seals, sharks and killer whales. When on land the adult \penguins have no predators. However introduced land predators as feral dogs, foxes, cats and stoats (a member of the weasel family) prey on eggs and chicks. Antarctic and subantarctic eggs and chicks are susceptible to antarctic skuas, sheath bills and giant petrels.
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Human Influence
Humans probably have hunted penguins and eggs for centuries. Mass exploitation occurred when early explorers, whalers, sealers turned to penguin colonies as a source of fresh meat and eggs. During much of the 19th century and into the 20th century penguins skins were used to make caps, slippers and purses. Feathers were used for clothing decorations and as mattress stuffing. The extraction of oil from penguins' fat layers became economically important in the 1800's and early 1900's. Oil was used for lighting, tanning leather, and fuel. Over a 16 years period an estimated 2.5 million penguins were killed in the Falkland Islands. Introduced predators have caused the decline of many different penguin species. Human construction can of course affect penguins as well as ecotourism. Oil spills are a continuing threat.
At Sea
Some penguins spend up to 75% of their lives at sea. Some species spend several months at sea coming ashore to breed and molt. Swimming speeds are not well known. The fastest swimmers belong to the genus Aptenodytes. Emperors have been observed swimming at 8.9 mph. Both the King and Chinstrap have been recorded at 5.3 mph, Adelies at 4.9 mph and little penguins at 1.6 mph. Most penguins porpoise and can maintain a steady speed of 4.3 to 6.2 mph. Porpoising may confuse predators. Since most of the prey of penguins inhabit the upper water layers, most penguins do not have to dive to great depths for long periods of time. Most species stay submerged for less than a minute, but the Gentoo and Adelie penguins have been recorded staying under water for seven minutes. During deep dives the penguin heart rate slows. Adelie and Gentoo penguins heart rate goes from 80 to 100 bpm to 20 bpm with deep dives. The Emperor's heart rate fall 15%. Like other sea birds, penguins have glands in the bill that help rid the body of excess salt. So effective are these glands that penguins can drink salt water without any adverse effects.
Senses
Penguins sleep with their bill tucked behind the flipper. To conserve energy while fasting, penguins may increase the time they spend sleeping. The internal temperature range of penguins is 100 F to 102 F. They conserve or release body heat to maintain body temperature through their circulatory system, much as human's do. There is vasoconstriction when the body is too cold and vasodilatation when the body becomes too warm.
As in most birds, the penguin hearing is thought to be good, but not as good as marine mammals. While hearing for penguins has not been well studied, vocalization has. Vocalizations (calls) are important in communication and mate recognition, particularly in penguin rookeries of many thousands of birds. Penguin eyes are adapted for underwater vision.. On land penguins are nearsighted. Penguins have exhibited color vision, sensitive to blue, green and violet light. Sense of taste in birds is poorly developed in birds and assumed to be in penguins also. Penguins have some sense of smell and the olfactory lobe of the penguin brain is large.