Editing Penguin (section)

==Anatomy and physiology==
[[File:Penguin Wing.svg|thumb|Penguin wings have the same general bone structure as flighted birds, but the bones are shorter and stouter to allow them to serve as fins. 1). Humerus 2). Sesamoid Bone 3). Radius 4). Ulna 5). Radial Carpal bone 6). Carpometacarpus 7). Phalanges]]
[[File:Taxidermy of a penguin skin.jpg|thumb|Taxidermized penguin skin]]
Penguins are superbly adapted to [[Aquatic ecosystem|aquatic]] life. Their [[wing]]s have evolved to become flippers, useless for flight in the air. In the water, however, penguins are astonishingly agile. Penguins' swimming looks very similar to birds' flight in the air.<ref>{{cite web |url=https://www.youtube.com/watch?v=knZ6E_YV4_c |title=Penguin swimming under water, Galapagos |publisher=Youtube.com |date=April 14, 2008 |access-date=September 8, 2013 |archive-url=https://web.archive.org/web/20140608005622/http://www.youtube.com/watch?v=knZ6E_YV4_c |archive-date=June 8, 2014 |url-status=live }}</ref> Within the smooth [[plumage]] a layer of air is preserved, ensuring buoyancy. The air layer also helps insulate the birds in cold waters. On land, penguins use their [[tail]]s and wings to maintain balance for their upright stance.

All penguins are [[Countershading|countershaded]] for [[camouflage]] – that is, they have black backs and [[wing]]s with white fronts.<ref>{{cite book|last=Buskey|first=Theresa|title=The Polar Regions|editor=Alan Christopherson, M.S.|publisher=Alpha Omegan Publications, Inc|location=804 N. 2nd Ave. E., Rock Rapids, IA|series=LIFEPAC|chapter=The Antarctic Polar Region|date=March 2001|isbn=978-1-58095-156-2}}</ref> 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.

Gentoo penguins are the fastest underwater birds in the world. They are capable of reaching speeds up to 36&nbsp;km (about 22 miles) per hour while searching for food or escaping from predators. They are also able to dive to depths of 170–200 meters (about 560–660 feet).<ref>{{cite news |last1=Rafferty |first1=John |title=Gentoo Penguin |url=https://www.britannica.com/animal/gentoo-penguin |newspaper=Encyclopedia Britannica |publisher=Encyclopedia Britannica Inc. |access-date=January 20, 2021 |archive-date=January 25, 2021 |archive-url=https://web.archive.org/web/20210125133319/https://www.britannica.com/animal/gentoo-penguin |url-status=live }}</ref> 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. Emperor penguins are the world's deepest-diving birds. They can dive to depths of approximately {{convert|550|m|ft|abbr=off|sp=us}} while searching for food.<ref>{{cite web|last1=Rafferty |first1=John |title=Emperor Penguin |url=https://www.britannica.com/animal/emperor-penguin |website=Britannica Online Encyclopedia |publisher=Britannica Encyclopedia Inc. |access-date=January 20, 2021 |archive-date=January 25, 2021 |archive-url=https://web.archive.org/web/20210125140129/https://www.britannica.com/animal/emperor-penguin |url-status=live}}</ref>

Penguins either waddle on their feet or slide on their bellies across the snow while using their feet to propel and steer themselves, a movement called "tobogganing", 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.

Penguins have an average sense of [[hearing (sense)|hearing]] for birds;<ref name="Wever">{{Cite journal
 | pmid = 5259756|jstor=59401
| pmc = 223504
| year = 1969
| last1 = Wever
| first1 = E. G.
| title = Hearing in the blackfooted penguin, ''Spheniscus demersus'', as represented by the cochlear potentials
| journal = Proceedings of the National Academy of Sciences of the United States of America
| volume = 63
| issue = #3
| pages = 676–80
| last2 = Herman
| first2 = P. N.
| last3 = Simmons
| first3 = J. A.
| last4 = Hertzler
| first4 = D. R.
 | doi=10.1073/pnas.63.3.676
| bibcode = 1969PNAS...63..676W
|doi-access=free
}}</ref> this is used by parents and chicks to locate one another in crowded [[Seabird colony|colonies]].<ref name="Jouventin">{{Cite journal
| pmid = 10373249
| year = 1999
| last1 = Jouventin
| first1 = P
| title = Finding a parent in a king penguin colony: The acoustic system of individual recognition
| journal = Animal Behaviour
| volume = 57
| issue = #6
| pages = 1175–1183
| last2 = Aubin
| first2 = T
| last3 = Lengagne
| first3 = T
| doi = 10.1006/anbe.1999.1086
| s2cid = 45578269
}}</ref> Their eyes are adapted for underwater vision 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.<ref name="Sivak">{{Cite journal
 | pmid = 2881308|jstor=36191
| year = 1987
| last1 = Sivak
| first1 = J
| title = Vision of the Humboldt penguin (''Spheniscus humboldti'') in air and water
| journal = Proceedings of the Royal Society of London B
| volume = 229
| issue = #1257
| pages = 467–72
| last2 = Howland
| first2 = H. C.
| last3 = McGill-Harelstad
| first3 = P
 | doi=10.1098/rspb.1987.0005
| bibcode = 1987RSPSB.229..467S
|s2cid=32860474
}}</ref>
[[File:Pygoscelis papua -Nagasaki Penguin Aquarium -swimming underwater-8a.jpg|thumb|left|[[Gentoo penguin]] swimming underwater at the Nagasaki Penguin Aquarium]]
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 [[emperor penguin]] 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 [[afterfeather]]s<!-- Can somebody make a page for this. I can not make this page myself -->, [[Down feather|plumule]]s, and [[filoplume]]s. The afterfeathers 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 plumules are small down feathers that attach directly to the skin, and are much more dense in penguins than other birds; lastly the filoplumes are small (less than 1&nbsp;cm long) naked shafts that end in a splay of fibers— filoplumes 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.<ref>{{cite news|title=Busting Myths About Penguin Feathers|author=Ed Young|date=October 20, 2015|url=https://www.nationalgeographic.com/science/phenomena/2015/10/20/busting-myths-about-penguin-feathers/|work=National Geographic|access-date=October 7, 2018|archive-url=https://web.archive.org/web/20181007183640/https://www.nationalgeographic.com/science/phenomena/2015/10/20/busting-myths-about-penguin-feathers/|archive-date=October 7, 2018|url-status=dead}}</ref>

The emperor penguin 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 huddle together to keep warm and rotate positions to make sure that each penguin gets a turn in the centre of the heat pack.

Calculations of the heat loss and retention ability of marine endotherms<ref name="Calculating">{{cite journal|last1=Downhower|first1=J.F.|last2=Blumer|first2=L.S.|title=Calculating just how small a whale can be|journal=Nature|date=1988|volume=335|pages=675|doi=10.1038/335675b0|pmid=3173490|issue=#6192|bibcode=1988Natur.335..675D|s2cid=47562824}}</ref> suggest that most extant penguins are too small to survive in such cold environments.<ref name="The penguins">{{cite book|last1=Williams|first1=T.D.|title=The penguins: Spheniscidae|date=1995|publisher=Oxford University Press|location=New York}}</ref> In 2007, Thomas and Fordyce wrote about the "heterothermic loophole" that penguins utilize in order to survive in Antarctica.<ref name="The heterothermic loophole exploited by penguins">{{cite journal |last1=Thomas |first1=D.B. |last2=Fordyce |first2=R.E. |author-link2=Ewan Fordyce |date=2007 |title=The heterothermic loophole exploited by penguins |journal=Australian Journal of Zoology |volume=55 |issue=#5 |pages=317–321 |doi=10.1071/zo07053}}</ref> 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 axillary artery, 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.<ref name="Biological plasticity in penguin heat-retention structures">{{cite journal|last1=Thomas|first1=D.B.|last2=Fordyce|first2=R.E.|title=Biological plasticity in penguin heat-retention structures|journal=Anatomical Record|date=2012|volume=295|issue=#2|pages=249–256|doi=10.1002/ar.21538|pmid=22213564|s2cid=23175291|doi-access=}}</ref>

They can drink salt water because their [[supraorbital gland]] filters excess salt from the bloodstream.<ref>{{cite web |url=http://www.zoo.org/educate/fact_sheets/penguin/penguin.htm |title=Animal Fact Sheets |access-date=July 21, 2006 |url-status=dead |archive-url=https://web.archive.org/web/20060720223700/http://www.zoo.org/educate/fact_sheets/penguin/penguin.htm |archive-date=July 20, 2006 }}</ref><ref>{{cite web |url=http://www.stlzoo.org/animals/abouttheanimals/birds/penguins/humboldtpenguin.htm |title=Humboldt Penguin: Saint Louis Zoo |access-date=July 21, 2006 |url-status=dead |archive-url=https://web.archive.org/web/20060928083710/http://www.stlzoo.org/animals/abouttheanimals/birds/penguins/humboldtpenguin.htm |archive-date=September 28, 2006 }}</ref><ref>{{cite web|url=http://users.iafrica.com/b/bo/boulders/Vans%20book.htm|author=van der Merwe, H.J.|work=iafrica.com|title=African Penguins and Penguins of the World|access-date=July 21, 2006|archive-url=https://web.archive.org/web/20061012221527/http://users.iafrica.com/b/bo/boulders/Vans%20book.htm|archive-date=October 12, 2006|url-status=dead}}</ref> The salt is excreted in a concentrated fluid from the nasal passages.

The [[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 [[convergent evolution]].<ref>[http://evo.bio.psu.edu/hedgeslab/Publications/PDF-files/128.pdf Convergence and divergence in the evolution of aquatic birds] {{webarchive|url=https://web.archive.org/web/20080529081926/http://evo.bio.psu.edu/hedgeslab/Publications/PDF-files/128.pdf |date=May 29, 2008 }} by Marcel Van Tuinen, Dave Brian Butvill, John A. W. Kirsch and S. Blair Hedges.</ref>

[[File:Penguins on Gourdin Island.jpg|thumb|An [[Isabelline (colour)|isabelline]] [[Adélie penguin]] on [[Gourdin Island]]]]
Around one in 50,000 penguins (of most species) are born with brown rather than black plumage. These are called [[Isabelline (colour)|isabelline]] penguins. Isabellinism is different from albinism. Isabelline penguins tend to live shorter lives than normal penguins, as they are not well-camouflaged against the deep and are often passed over as mates.