Editing Owl (section)

== Anatomy ==
[[File:Chouettes.jpg|thumb|left|[[Tawny owl]] (''Strix aluco''), left, and [[western barn owl]] (''Tyto alba''), right, belonging respectively to the [[Strigidae]] and [[Tytonidae]] families]]
[[File:Athene cuniculariaa.jpg|thumb|upright|[[Burrowing owl]] (''Athene cunicularia'')]]

Owls possess large, forward-facing eyes and ear-holes, a [[hawk]]-like [[beak]], a flat face, and usually a conspicuous circle of feathers, a [[facial disc]], around each eye. The feathers making up this disc can be adjusted to sharply focus sounds from varying distances onto the owls' asymmetrically placed ear cavities. Most birds of prey have eyes on the sides of their heads, but the stereoscopic nature of the owl's forward-facing eyes permits the greater sense of [[depth perception]] necessary for low-light hunting. Owls have [[binocular vision]], but they must rotate their entire heads to change the focus of their view because, like most birds, their eyes are fixed in their sockets. Owls are farsighted and cannot clearly see anything nearer than a few centimetres of their eyes. Caught prey can be felt by owls with the use of [[filoplume]]s—hairlike feathers on the beak and feet that act as "feelers". Their far vision, particularly in low light, is exceptionally good.

Owls can rotate their heads and necks as much as 270°. Owls have 14 neck vertebrae — humans have only seven — and their vertebral circulatory systems are adapted to allow them to rotate their heads without [[cerebral infarction|cutting off blood to the brain]]. Specifically, the [[Intervertebral foramina|foramina]] in their vertebrae through which the vertebral arteries pass are about ten times the diameter of the artery, instead of about the same size as the artery, as is the case in humans; the vertebral arteries enter the [[cervical vertebra]]e higher than in other birds, giving the vessels some slack, and the [[carotid artery|carotid arteries]] unite in a very large [[anastomosis]] or junction, the largest of any bird's, preventing blood supply from being cut off while they rotate their necks. Other anastomoses between the carotid and vertebral arteries support this effect.<ref>{{Cite journal|title=International Science & Engineering Visualization Challenge: Posters & Graphics|journal=Science|date=1 February 2013|volume=339|issue=6119|pages=514–515|doi=10.1126/science.339.6119.514|doi-access=}}</ref><ref>{{cite web|title=Owl mystery unraveled: Scientists explain how bird can rotate its head without cutting off blood supply to brain| url=http://www.hopkinsmedicine.org/news/media/releases/owl_mystery_unraveled_scientists_explain_how_bird_can_rotate_its_head_without_cutting_off_blood_supply_to_brain|date=31 January 2013|publisher=Johns Hopkins Medicine|access-date=2013-03-03}}</ref>

The smallest owl—weighing as little as {{convert|31|g|oz|frac=32|abbr=on}} and measuring some {{convert|13.5|cm|in|frac=4|abbr=on}}—is the [[elf owl]] (''Micrathene whitneyi'').<ref name="Owls">Konig, Claus; Welck, Friedhelm and Jan-Hendrik Becking (1999) ''Owls: A Guide to the Owls of the World'', Yale University Press, {{ISBN|978-0-300-07920-3}}.</ref>  Around the same diminutive length, although slightly heavier, are the lesser known [[long-whiskered owlet]] (''Xenoglaux loweryi'') and [[Tamaulipas pygmy owl]] (''Glaucidium sanchezi'').<ref name="Owls"/> The largest owls are two similarly sized species; the [[Eurasian eagle-owl]] (''Bubo bubo'') and [[Blakiston's fish owl]] (''Ketupa blakistoni''). The largest females of these species are {{convert|71|cm|in|frac=2|abbr=on}} long, have a {{convert|190|cm|in|abbr=on}} wing span, and weigh {{convert|4.2|kg|lb|frac=4|abbr=on}}.<ref name="Owls"/><ref>[http://www.oiseaux-birds.com/card-eurasian-eagle-owl.html Eurasian Eagle Owl]. Oiseaux-birds.com. Retrieved 2013-03-02.</ref><ref>[http://www.owlpages.com/owls.php?genus=Bubo&species=bubo Eurasian Eagle Owl – Bubo bubo – Information, Pictures, Sounds]. Owlpages.com (13 August 2012). Retrieved 2013-03-02.</ref><ref>[http://quillcards.com/blog/index.php/2009/09/23/take-a-peek-at-boo-the-eagle-owl/ Take A Peek At Boo, The Eagle Owl – The Quillcards Blog] {{Webarchive|url=https://web.archive.org/web/20150426061347/http://quillcards.com/blog/index.php/2009/09/23/take-a-peek-at-boo-the-eagle-owl/ |date=26 April 2015 }}. Quillcards.com (23 September 2009). Retrieved 2013-03-02.</ref><ref>[http://www.fishowls.com/ Blakiston's Fish Owl Project]. Fishowls.com (26 February 2013). Retrieved 2013-03-02.</ref>

Different species of owls produce different sounds; this distribution of calls aids owls in finding mates or announcing their presence to potential competitors, and also aids [[ornithologist]]s and [[birder]]s in locating these birds and distinguishing species. As noted above, their facial discs help owls to funnel the sound of prey to their ears. In many species, these discs are placed asymmetrically, for better directional location.

Owl [[plumage]] is generally [[crypsis|cryptic]], although several species have facial and head markings, including face masks, [[ear tuft]]s, and brightly colored [[Iris (anatomy)|iris]]es. These markings are generally more common in species inhabiting open habitats, and are thought to be used in signaling with other owls in low-light conditions.<ref>{{cite journal|last=Galeotti|first=Paolo |author2=Diego Rubolini|date=November 2007|title=Head ornaments in owls: what are their functions? |journal=Journal of Avian Biology|volume=38|issue=6|pages=731–736 | doi = 10.1111/j.0908-8857.2007.04143.x}}</ref>

=== Sexual dimorphism ===
[[File:Owl. Birds - defenders of the forest. USSR stamp. 1979.jpg|thumb|A stamp from the Soviet Union, 1979]]
[[Sexual dimorphism]] is a physical difference between males and females of a species. Female owls are typically larger than the males.<ref name=":0">{{Cite journal|title = Adaptive advantages of reversed sexual size dimorphism in European owls|last = Lundberg|first = Arne|date = May 1986|journal = Ornis Scandinavica|volume = 17|issue = 2|pages = 133–140|doi = 10.2307/3676862|jstor = 3676862}}</ref> The degree of size dimorphism varies across multiple populations and species, and is measured through various traits, such as wing span and body mass.<ref name=":0" />

One theory suggests that selection has led males to be smaller because it allows them to be efficient [[Foraging|foragers]]. The ability to obtain more food is advantageous during breeding season. In some species, female owls stay at their nest with their eggs while it is the responsibility of the male to bring back food to the nest.<ref name=":2">{{Cite journal|url = https://sora.unm.edu/sites/default/files/journals/wilson/p0387-p0406.pdf|title = The evolution of reversed sexual size dimorphism in hawks, falcons and owls: a comparative study|last = Krüger|first = Oliver|date = September 2005|journal = Evolutionary Ecology|volume = 19|issue = 5|pages = 467–486|doi = 10.1007/s10682-005-0293-9|s2cid = 22181702}}</ref> If food is scarce, the male first feeds himself before feeding the female.<ref name=":1">{{Cite journal|url = https://sora.unm.edu/sites/default/files/journals/wilson/p0387-p0406.pdf|title = The evolution of reversed sexual dimorphism in owls: an empirical analysis of possible selective factors|last = Mueller|first = H.C.|date = 1986|journal = The Wilson Bulletin|volume = 19|issue = 5|page = 467|doi = 10.1007/s10682-005-0293-9|s2cid = 22181702}}</ref> Small birds, which are agile, are an important source of food for owls. Male burrowing owls have been observed to have longer wing chords than females, despite being smaller than females.<ref name=":1" /> Furthermore, owls have been observed to be roughly the same size as their prey.<ref name=":1" /> This has also been observed in other predatory birds,<ref name=":2" /> which suggests that owls with smaller bodies and long wing chords have been selected for because of the increased agility and speed that allows them to catch their prey.{{citation needed|date=July 2019}}

Another popular theory suggests that females have not been selected to be smaller like male owls because of their sexual roles. In many species, female owls may not leave the nest. Therefore, females may have a larger mass to allow them to go for a longer period of time without starving. For example, one hypothesized sexual role is that larger females are more capable of dismembering prey and feeding it to their young, hence female owls are larger than their male counterparts.<ref name=":0" />

A different theory suggests that the size difference between male and females is due to sexual selection: since large females can choose their mate and may violently reject a male's sexual advances, smaller male owls that have the ability to escape unreceptive females are more likely to have been selected.<ref name=":1" />

If the character is stable, there can be different optimums for both sexes. Selection operates on both sexes at the same time; therefore it is necessary to explain not only why one of the sexes is relatively bigger, but also why the other sex is smaller.<ref>Székely T, Freckleton R. P., Reynolds J. D. (2004) Sexual selection explains Rensch's rule of size dimorphism in shorebirds. ''PNAS'', '''101''', N. 33, p. 12224–12227.</ref> If owls are still evolving toward smaller bodies and longer wing chords, according to V. Geodakyan's Evolutionary Theory of Sex, males should be more advanced on these characters. Males are viewed as an evolutionary vanguard of a population, and sexual dimorphism on the character, as an evolutionary "distance" between the sexes.  "Phylogenetic rule of sexual dimorphism" states that if there exists a sexual dimorphism on any character, then the evolution of this trait goes from the female form toward the male one.<ref>Geodakyan V. A. (1985) Sexual dimorphism. In: Evolution and morphogenesis. (Mlikovsky J., Novak V. J. A., eds.), Academia, Praha, p. 467–477.</ref>

=== Hunting adaptations ===
All owls are carnivorous birds of prey and live on diets of insects, small rodents and lagomorphs. Some owls are also specifically adapted to hunt fish. They are very adept in hunting in their respective environments. Since owls can be found in nearly all parts of the world and across a multitude of ecosystems, their hunting skills and characteristics vary slightly from species to species, though most characteristics are shared among all species.<ref>{{Cite web |date=2023-05-28 |title=Are Owls Omnivores Herbivores or Carnivores? [Answered!] |url=https://birdsatfirstsight.com/are-owls-omnivores-herbivores-or-carnivores/ |access-date=2023-07-24 |website=Birds at First Sight |language=en-US}}</ref>

==== Flight and feathers ====
{{external media|width=230px|video1=[https://www.youtube.com/watch?v=d_FEaFgJyfA Experiment! How Does An Owl Fly So Silently?], from [[BBC Earth]]}}
Most owls share an innate ability to fly almost silently and also more slowly in comparison to other birds of prey. Most owls live a mainly nocturnal lifestyle and being able to fly without making any noise gives them a strong advantage over prey alert to the slightest sound in the night. A silent, slow flight is not as necessary for diurnal and crepuscular owls given that prey can usually see an owl approaching. Owls' feathers are generally larger than the average birds' feathers, have fewer radiates, longer pennulum, and achieve smooth edges with different [[rachis]] structures.<ref name="Bachmann2007"/> Serrated edges along the owl's remiges bring the flapping of the wing down to a nearly silent mechanism. The serrations are more likely reducing aerodynamic disturbances, rather than simply reducing noise.<ref>{{Cite news|last=Stevenson|first=John|date=November 18, 2020|title=Small finlets on owl feathers point the way to less aircraft noise|work=[[Phys.org]]|url=https://phys.org/news/2020-11-small-finlets-owl-feathers-aircraft.html|access-date=November 20, 2020}}</ref> The surface of the flight feathers is covered with a velvety structure that absorbs the sound of the wing moving. These unique structures reduce noise frequencies above 2&nbsp;kHz,<ref name="Neuhaus1973"/> making the sound level emitted drop below the typical hearing spectrum of the owl's usual prey<ref name="Neuhaus1973"/><ref name=Willott/> and also within the owl's own best hearing range.<ref>{{cite journal |last1=Dyson |first1=M. L. |last2=Klump |first2=G. M. |last3=Gauger |first3=B. |title=Absolute hearing thresholds and critical masking ratios in the European barn owl: a comparison with other owls |journal=Journal of Comparative Physiology |date=April 1998 |volume=182 |issue=5 |pages=695–702 |doi=10.1007/s003590050214|s2cid=24641904 }}</ref><ref>{{cite book |last1=Webster |first1=Douglas B. |last2=Fay |first2=Richard R. |title=The Evolutionary Biology of Hearing |date=December 6, 2012 |publisher=Springer Science & Business Media |isbn=978-1-4612-2784-7 |page=547 |chapter=Hearing in Birds}}</ref> This optimizes the owl's ability to silently fly to capture prey without the prey hearing the owl first as it flies, and to hear any noise the prey makes. It also allows the owl to monitor the sound output from its flight pattern.
[[File:Great Horned Owl in a Rain Storm in the Mojave.jpg|thumb|right|A [[great horned owl]] with wet [[feathers]], waiting out a [[rainstorm]]]]

The disadvantage of such feather adaptations for barn owls is that their feathers are not waterproof.<ref name="auto">{{cite web|url=https://sussexwildlifetrust.org.uk/news/barn-owl-feathers|first=Charlotte|last=Owen|title=Barn Owl feathers|publisher=[[Sussex Wildlife Trust]]|date=23 August 2022|access-date=11 February 2024}}</ref> The adaptations mean that barn owls do not use the [[uropygial gland]], informally the "preen" or "oil" gland, as most birds do, to spread oils across their plumage through preening.<ref>{{cite web|url=https://www.aiwc.ca/blog/unveiling-the-intricate-mechanisms-of-avian-waterproofing/|first=Julia|last=Gaume|title=Unveiling the intricate mechanisms of avian waterproofing|publisher=Alberta Institute for Wildlife Conservation|date=26 July 2023|access-date=13 February 2024}}</ref> This makes them highly vulnerable to heavy rain when they are unable to hunt.<ref>{{cite web|url=https://www.barnowltrust.org.uk/barn-owl-facts/barn-owl-adaptations/#:~:text=Compared%20with%20other%20birds%2C%20Barn,increase%20noise%20and%20reduce%20efficiency.|title=Barn Owl adaptations|publisher=[[Barn Owl Trust]]|access-date=11 February 2024}}</ref> Historically, they would switch to hunting indoors in wet weather, using [[barn]]s and other agricultural buildings, but the decline in the numbers of these structures in the 20th and 21st centuries has reduced such opportunities.<ref name="auto"/> The lack of waterproofing means that barn owls are also susceptible to drowning, in [[Manger|drinking troughs]] and other structures with smooth sides. The [[Barn Owl Trust]] provides advice on how this can be mitigated, by the installation of floats.<ref>{{cite web|url=https://www.barnowltrust.org.uk/hazards-solutions/water-troughs-barn-owls/|title=Barn Owl Hazards: Water troughs|publisher=[[Barn Owl Trust]]|access-date=11 February 2024}}</ref>

==== Vision ====
Eyesight is a particular characteristic of the owl that aids in nocturnal prey capture. Owls are part of a small group of birds that live nocturnally, but do not use [[Animal echolocation|echolocation]] to guide them in flight in low-light situations. Owls are known for their disproportionally large eyes in comparison to their skulls. An apparent consequence of the evolution of an absolutely large eye in a relatively small skull is that the eye of the owl has become tubular in shape. This shape is found in other so-called nocturnal eyes, such as the eyes of [[Strepsirrhini|strepsirrhine]] [[primate]]s and [[bathypelagic fish]]es.<ref name="Walls1942"/> Since the eyes are fixed into these sclerotic tubes, they are unable to move the eyes in any direction.<ref name="König1999"/> Instead of moving their eyes, owls swivel their heads to view their surroundings. Owls' heads are capable of swiveling through an angle of roughly 270°, easily enabling them to see behind them without relocating the torso.<ref name="König1999"/> This ability keeps bodily movement at a minimum, thus reduces the amount of sound the owl makes as it waits for its prey. Owls are regarded as having the most frontally placed eyes among all avian groups, which gives them some of the largest binocular fields of vision. Owls are farsighted and cannot focus on objects within a few centimetres of their eyes.<ref name="Walls1942"/><ref name=Hughes/> These mechanisms are only able to function due to the large-sized retinal image.<ref name="Martin1982"/> Thus, the primary nocturnal function in the vision of the owl is due to its large posterior nodal distance; retinal image brightness is only maximized to the owl within secondary neural functions.<ref name="Martin1982"/> These attributes of the owl cause its nocturnal eyesight to be far superior to that of its average prey.<ref name="Martin1982"/>

==== Hearing ====
[[File: Great Horned Owl at twilight, Mojave Desert.jpg|thumb|right|A [[great horned owl]] perched on the top of a Joshua tree at evening ([[twilight]]) in the [[Mojave Desert]], U.S.]]
{{further|Sound localization in owls}}

Owls exhibit specialized hearing functions and ear shapes that also aid in hunting. They are noted for asymmetrical ear placements on the skull in some genera. Owls can have either internal or external ears, both of which are asymmetrical. Asymmetry has not been reported to extend to the middle or internal ear of the owl. Asymmetrical ear placement on the skull allows the owl to pinpoint the location of its prey. This is especially true for strictly nocturnal species such as the barn owls ''Tyto'' or Tengmalm's owl.<ref name=" König1999"/> With ears set at different places on its skull, an owl is able to determine the direction from which the sound is coming by the minute difference in time that it takes for the sound waves to penetrate the left and right ears.<ref>{{Cite news |last=Knudsen |first=Eric I. |date=1 December 1981 |url=https://www.scientificamerican.com/article/the-hearing-of-the-barn-owl/ |title=The Hearing of the Barn Owl |work=Scientific American}}</ref> The owl turns its head until the sound reaches both ears at the same time, at which point it is directly facing the source of the sound. This time difference between ears is about 30 microseconds. <!-- Like the eyes, which use feather movements to focus light,{{citation needed|date=January 2014}}{{dubious|date=January 2014}} the ears are surrounded by feathers to maximize hearing capabilities. --> Behind the ear openings are modified, dense feathers, densely packed to form a facial ruff, which creates an anterior-facing, concave wall that cups the sound into the ear structure.<ref name=Norberg/> This facial ruff is poorly defined in some species, and prominent, nearly encircling the face, in other species. The facial disk also acts to direct sound into the ears, and a downward-facing, sharply triangular beak minimizes sound reflection away from the face. The shape of the facial disk is adjustable at will to focus sounds more effectively.<ref name="König1999"/>

The prominences above a great horned owl's head are commonly mistaken as its ears. This is not the case; they are merely feather tufts. The ears are on the sides of the head in the usual location (in two different locations as described above).

==== Talons ====
While the auditory and visual capabilities of the owl allow it to locate and pursue its prey, the talons and beak of the owl do the final work. The owl kills its prey using these talons to crush the skull and knead the body.<ref name="König1999"/> The crushing power of an owl's talons varies according to prey size and type, and by the size of the owl. The burrowing owl (''Athene cunicularia''), a small, partly insectivorous owl, has a release force of only 5&nbsp;N. The larger [[Western barn owl|barn owl]] (''Tyto alba'') needs a force of 30&nbsp;N to release its prey, and one of the largest owls, the [[great horned owl]] (''Bubo virginianus''), needs a force over 130&nbsp;N to release prey in its talons.<ref name="Marti1974"/> An owl's talons, like those of most birds of prey, can seem massive in comparison to the body size outside of flight. The [[Tyto novaehollandiae castanops|Tasmanian masked owl]] has some of the proportionally longest talons of any bird of prey; they appear enormous in comparison to the body when fully extended to grasp prey.<ref name="Einoder2007"/> An owl's claws are sharp and curved. The family Tytonidae has inner and central toes of about equal length, while the family Strigidae has an inner toe that is distinctly shorter than the central one.<ref name="Marti1974"/> These different morphologies allow efficiency in capturing prey specific to the different environments they inhabit.

==== Beak ====
The beak of the owl is short, curved, and downward-facing, and typically hooked at the tip for gripping and tearing its prey. Once prey is captured, the scissor motion of the top and lower bill is used to tear the tissue and kill. The sharp lower edge of the upper bill works in coordination with the sharp upper edge of the lower bill to deliver this motion. The downward-facing beak allows the owl's field of vision to be clear, as well as directing sound into the ears without deflecting sound waves away from the face.<ref>{{Cite web|last=Shamim1410|date=2020-04-22|title=Owl Bird Traits, Adaptations and Surprising Facts|url=https://www.birdbaron.com/owl-bird/|access-date=2022-02-04|website=Bird Baron|language=en-US}}</ref>

==== Camouflage ====
[[File:Harfang en vol 1.jpg|thumb|The [[snowy owl]] has effective [[snow camouflage]]]]

The coloration of the owl's plumage plays a key role in its ability to sit still and blend into the environment, making it nearly invisible to prey. Owls tend to mimic the coloration and sometimes the texture patterns of their surroundings, the barn owl being an exception. The [[snowy owl]] (''Bubo scandiacus'') appears nearly bleach-white in color with a few flecks of black, mimicking their snowy surroundings perfectly, while the speckled brown plumage of the [[tawny owl]] (''Strix aluco'') allows it to lie in wait among the deciduous woodland it prefers for its habitat. Likewise, the [[mottled wood owl]] (''Strix ocellata'') displays shades of brown, tan, and black, making the owl nearly invisible in the surrounding trees, especially from behind. Usually, the only tell-tale sign of a perched owl is its vocalizations or its vividly colored eyes.