var presentation = ["<word>adapted to aquatic life<\/word>","<word>useless for flight<\/word>","<word>buoyancy<\/word>","<phrase>Penguins are superbly <strong data-readahead=\"adapted to aquatic life\" class=\"presentation_word\">adapted to aquatic life<\/strong>. Their wings have evolved to become flippers, <strong data-readahead=\"useless for flight\" class=\"presentation_word\">useless for flight<\/strong> in the air. In the water, however, penguins are astonishingly agile. Penguins' swimming looks very similar to the bird's flight in the air. Within the smooth plumage, a layer of air is preserved, ensuring <strong data-readahead=\"buoyancy\" class=\"presentation_word\">buoyancy<\/strong>. The air layer also helps insulate the birds in cold waters. On land, penguins use their tails and wings to maintain balance for their upright stance.<\/phrase>","<word>countershaded for camouflage<\/word>","<phrase>All penguins are <strong data-readahead=\"countershaded for camouflage\" class=\"presentation_word\">countershaded for camouflage<\/strong> \u2013 that is, they have black backs and wings with white fronts. A predator looking up from below (such as an orca or a leopard seal) has difficulty distinguishing between a white penguin belly and the reflective water surface. The dark plumage on their backs camouflages them from above.<\/phrase>","<word>emperor penguin<\/word>","<phrase>Diving penguins reach 3.7 to 7.5 mph, though there are reports of velocities of 17 mph (which are more realistic in the case of startled flight). The small penguins do not usually dive deep; they catch their prey near the surface in dives that normally last only one or two minutes. Larger penguins can dive deep in case of need. Dives of the large <strong data-readahead=\"emperor penguin\" class=\"presentation_word\">emperor penguin<\/strong> have been recorded reaching a depth of 1,854 ft for up to 22 minutes.<\/phrase>","<word>waddle on their feet<\/word>","<word>slide on their bellies<\/word>","<word>tobogganing<\/word>","<phrase>Penguins either <strong data-readahead=\"waddle on their feet\" class=\"presentation_word\">waddle on their feet<\/strong> or <strong data-readahead=\"slide on their bellies\" class=\"presentation_word\">slide on their bellies<\/strong> across the snow while using their feet to propel and steer themselves, a movement called \"<strong data-readahead=\"tobogganing\" class=\"presentation_word\">tobogganing<\/strong>\", which conserves energy while moving quickly. They also jump with both feet together if they want to move more quickly or cross steep or rocky terrain.<\/phrase>","<word>underwater vision<\/word>","<phrase>Penguins have an average sense of hearing for birds; this is used by parents and chicks to locate one another in crowded colonies. Their eyes are adapted for <strong data-readahead=\"underwater vision\" class=\"presentation_word\">underwater vision<\/strong>, and are their primary means of locating prey and avoiding predators; in air it has been suggested that they are nearsighted, although research has not supported this hypothesis.<\/phrase>","<word>emperor penguin<\/word>","<word>afterfeathers<\/word>","<word>plumules<\/word>","<word>filoplumes<\/word>","<phrase>Penguins have a thick layer of insulating feathers that keeps them warm in water (heat loss in water is much greater than in air). The <strong data-readahead=\"emperor penguin\" class=\"presentation_word\">emperor penguin<\/strong> has a maximum feather density of about nine feathers per square centimeter which is actually much lower than other birds that live in antarctic environments. However, they have been identified as having at least four different types of feather: in addition to the traditional feather, the emperor has <strong data-readahead=\"afterfeathers\" class=\"presentation_word\">afterfeathers<\/strong>, <strong data-readahead=\"plumules\" class=\"presentation_word\">plumules<\/strong>, and <strong data-readahead=\"filoplumes\" class=\"presentation_word\">filoplumes<\/strong>. The <strong data-readahead=\"afterfeathers\">afterfeathers<\/strong> are downy plumes that attach directly to the main feathers and were once believed to account for the bird's ability to conserve heat when under water; the <strong data-readahead=\"plumules\">plumules<\/strong> are small down feathers that attach directly to the skin, and are much more dense in penguins than other birds; lastly the <strong data-readahead=\"filoplumes\">filoplumes<\/strong> are small (less than 1 cm long) naked shafts that end in a splay of fibers- <strong data-readahead=\"filoplumes\">filoplumes<\/strong> were believed to give flying birds a sense of where their plumage was and whether or not it needed preening, so their presence in penguins may seem inconsistent, but penguins also preen extensively.<\/phrase>","<word>emperor penguin<\/word>","<word>huddle together to keep warm<\/word>","<phrase>The <strong data-readahead=\"emperor penguin\" class=\"presentation_word\">emperor penguin<\/strong> has the largest body mass of all penguins, which further reduces relative surface area and heat loss. They also are able to control blood flow to their extremities, reducing the amount of blood that gets cold, but still keeping the extremities from freezing. In the extreme cold of the Antarctic winter, the females are at sea fishing for food leaving the males to brave the weather by themselves. They often <strong data-readahead=\"huddle together to keep warm\" class=\"presentation_word\">huddle together to keep warm<\/strong> and rotate positions to make sure that each penguin gets a turn in the centre of the heat pack.<\/phrase>","<word>marine endotherms<\/word>","<word>axillary artery<\/word>","<phrase>Calculations of the heat loss and retention ability of <strong data-readahead=\"marine endotherms\" class=\"presentation_word\">marine endotherms<\/strong> suggest that most extant penguins are too small to survive in such cold environments. In 2007, Thomas and Fordyce wrote about the \"heterothermic loophole\" that penguins utilize in order to survive in Antarctica. All extant penguins, even those that live in warmer climates, have a counter-current heat exchanger called the humeral plexus. The flippers of penguins have at least three branches of the <strong data-readahead=\"axillary artery\" class=\"presentation_word\">axillary artery<\/strong>, which allows cold blood to be heated by blood that has already been warmed and limits heat loss from the flippers. This system allows penguins to efficiently use their body heat and explains why such small animals can survive in the extreme cold.<\/phrase>","<word>can drink salt water<\/word>","<word>convergent evolution<\/word>","<phrase>They <strong data-readahead=\"can drink salt water\" class=\"presentation_word\">can drink salt water<\/strong> because their supraorbital gland filters excess salt from the bloodstream. The salt is excreted in a concentrated fluid from the nasal passages.\nThe great auk of the Northern Hemisphere, now extinct, was superficially similar to penguins, and the word penguin was originally used for that bird, centuries ago. They are only distantly related to the penguins, but are an example of <strong data-readahead=\"convergent evolution\" class=\"presentation_word\">convergent evolution<\/strong>.<\/phrase>"];
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