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The true owls or typical owls ( family Strigidae) are one of the two generally accepted families of owls, the other being the
barn owls The barn owl (''Tyto alba'') is the most widely distributed species of owl in the world and one of the most widespread of all species of birds, being found almost everywhere except for the polar and desert regions, Asia north of the Himalaya ...
(Tytonidae). This large family comprises 230 living or recently extinct
species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...
in 24 genera. The typical owls have a
cosmopolitan distribution In biogeography, cosmopolitan distribution is the term for the range of a taxon that extends across all or most of the world in appropriate habitats. Such a taxon, usually a species, is said to exhibit cosmopolitanism or cosmopolitism. The ext ...
and are found on every continent except
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...
.


Morphology

While typical owls (hereafter referred to simply as owls) vary greatly in size, with the smallest species, the
elf owl The elf owl (''Micrathene whitneyi'') is a small grayish-brown owl about the size of a sparrow found in the Southwestern United States, central Mexico, and the Baja California peninsula. It has pale yellow eyes highlighted by thin white "eyebrow ...
, being a hundredth the size of the largest, the
Eurasian eagle-owl The Eurasian eagle-owl (''Bubo bubo'') is a species of eagle-owl that resides in much of Eurasia. It is also called the Uhu and it is occasionally abbreviated to just the eagle-owl in Europe. It is one of the largest species of owl, and female ...
and
Blakiston's fish owl Blakiston's fish owl (''Bubo blakistoni''), the largest living species of owl, is a fish owl, a sub-group of eagle-owls which specialize in hunting in riparian areas. It is native to China, Japan, and the Russian Far East. This species is a part ...
, owls generally share an extremely similar body plan.Marks, J. S.; Cannings, R.J. and Mikkola, H. (1999). "Family Strigidae (Typical Owls)". ''In'' del Hoyo, J.; Elliot, A. & Sargatal, J. (eds.) (1999). '' Handbook of the Birds of the World. Volume 5: Barn-Owls to Hummingbirds.'' Lynx Edicions. They tend to have large heads, short tails, cryptic
plumage Plumage ( "feather") is a layer of feathers that covers a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage differ between species and subspecies and may vary with age classes. Within species, ...
, and round facial discs around the eyes. The family is generally
arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally, but others are exclusively arboreal. The habitats pose nu ...
(with a few exceptions like the
burrowing owl The burrowing owl (''Athene cunicularia''), also called the shoco, is a small, long-legged owl found throughout open landscapes of North and South America. Burrowing owls can be found in grasslands, rangelands, agricultural areas, deserts, or any ...
) and obtain their food on the wing. The wings are large, broad, rounded, and long. As is the case with most
birds of prey Birds of prey or predatory birds, also known as raptors, are hypercarnivorous bird species that actively hunt and feed on other vertebrates (mainly mammals, reptiles and other smaller birds). In addition to speed and strength, these predators h ...
, in many owl species females are larger than males. Because of their
nocturnal Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite. Nocturnal creatures generally have highly developed sens ...
habits, they tend not to exhibit sexual dimorphism in their plumage. Specialized feathers and wing shape suppress the noise produced by flying, both taking off, flapping and gliding. This silent flight allows owls to hunt without being heard by their prey. Owls possess three physical attributes that are thought to contribute to their silent flight capability. First, on the leading edge of the wing, there is a comb of stiff feathers. Second, the trailing edge of the wing contains a flexible fringe. Finally, owls have downy material distributed on the tops of their wings that creates a compliant but rough surface (similar to that of a soft carpet). All these factors result in significant aerodynamic noise reductions. The toes and tarsi are feathered in some species, and more so in species at higher latitudes. Numerous species of owls in the genus '' Glaucidium'' and the northern hawk-owl have eye patches on the backs of their heads, apparently to convince other birds they are being watched at all times. Numerous nocturnal species have ear-tufts, feathers on the sides of the head that are thought to have a
camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...
function, breaking up the outline of a roosting bird. The feathers of the facial disc are arranged in order to increase sound delivered to the ears. Hearing in owls is highly sensitive and the ears are asymmetrical allowing the owl to localise a sound in multiple directions. Owls can pinpoint the position of prey, such as a squeaking mouse, by computing when the sound from the object reaches the owl's ears. If the sound reaches the left ear first, the mouse must be to the left of the owl. The owl's brain will then direct the head to directly face the mouse. In addition to hearing, owls have massive eyes relative to their body size. Contrary to popular belief, however, owls cannot see well in extreme dark and are able to see well in the day. Owls are also able to rotate their heads by as much as 270 degrees in either direction without damaging the blood vessels in their necks and heads, and without disrupting blood flow to their brains. Researchers have found four major biological adaptations that allow for this unique capability. First, in the neck there is a major artery, called the vertebral artery, that feeds the brain. This artery passes through bony holes in the vertebra. These bony holes are ten times larger in diameter than the artery that passes through them (extra space in the transverse foramina). This creates cushiony air pockets that allow for more movement of the artery when twisted. 12 of the 14 cervical vertebrae in the owl's neck have this adaptation. This vertebral artery also enters the neck higher up than it does in other birds. Instead of going in at the 14th cervical vertebrae, it enters in at the 12th cervical vertebrae. Finally, the small vessel connection between the carotid and the vertebral arteries allow the exchanging of blood between two blood vessels. These cross connections allow for uninterrupted blood flow to the brain. This means that even if one route is blocked during extreme head rotations, another route can continue blood circulation to the brain. Several owl species also have fluorescent pigments called porphyrins under their wings. A large group of pigments defined by nitrogen-containing pyrole rings, including chlorophyll and heme (in animal blood), make up the porphyrins. Other bird species will use porphyrins to pigment eggshells in the oviduct. Owl species, however, use porphyrins as a pigment in their plumage. Porphyrins are most prevalent in new feathers and are easily destroyed by sunlight. Porphyrin pigments in feathers fluoresce under UV light, allowing biologists to more accurately classify the age of owls. The relative ages of the feathers are differentiated by the intensity of fluorescence that they emit when the primaries and secondaries are exposed to
black light A blacklight, also called a UV-A light, Wood's lamp, or ultraviolet light, is a lamp that emits long-wave ( UV-A) ultraviolet light and very little visible light. One type of lamp has a violet filter material, either on the bulb or in a sepa ...
. This method helps to detect the subtle differences between third and fourth generation feathers, whereas looking at wear and color makes age determination difficult.


Niche competition

It has been noted that there is some competition for niche space between the spotted owl and the
barred owl The barred owl (''Strix varia''), also known as the northern barred owl, striped owl or, more informally, hoot owl, is a North American large species of owl. A member of the true owl family, Strigidae, they belong to the genus '' Strix'', which ...
(both of which are true owls) . This competition is related to deforestation, and therefore a reduction in niche quantity and quality. This deforestation is more specifically the result of overlogging and
forest fires A wildfire, forest fire, bushfire, wildland fire or rural fire is an unplanned, uncontrolled and unpredictable fire in an area of combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identif ...
. These two species of owl are known to traditionally live in mature forests of old and tall trees, which at this point in time are mostly limited to public lands. As niche overlap is occurring in these two families, there is a concern with the barred owls encroaching on the spotted owl's North American habitats, causing a decline of the spotted owl. As noted above, these species prefer mature forests which, due to deforestation, are at limited supply and take a long time to reestablish after deforestation has occurred. Because the northern spotted owl shares its territories and competes with other species, it is declining at a more rapid pace. This invasion by barred owls occurred about 50 years ago in the Pacific Northwest, and despite their low numbers, they are considered an invasive species because of the harm done to native spotted owls. In this competition for resources, hunting locations and general niches, the barred owl is pushing the spotted owl to
local extinction Local extinction, also known as extirpation, refers to a species (or other taxon) of plant or animal that ceases to exist in a chosen geographic area of study, though it still exists elsewhere. Local extinctions are contrasted with global extinct ...
. It is thought that the rapid decrease in population size of spotted owls will cause a
trophic cascade Trophic cascades are powerful indirect interactions that can control entire ecosystems, occurring when a trophic level in a food web is suppressed. For example, a top-down cascade will occur if predators are effective enough in predation to reduce t ...
, since the spotted owls help provide a healthy ecosystem.


Behaviour

Owls are generally
nocturnal Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite. Nocturnal creatures generally have highly developed sens ...
and/or
crepuscular In zoology, a crepuscular animal is one that is active primarily during the twilight period, being matutinal, vespertine, or both. This is distinguished from diurnal and nocturnal behavior, where an animal is active during the hours of daylig ...
and spend much of the day
roosting Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight ...
. They are often misperceived as ‘tame’ since they allow humans to approach quite closely before taking flight, but in reality they are attempting to avoid detection through stillness. Their cryptic
plumage Plumage ( "feather") is a layer of feathers that covers a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage differ between species and subspecies and may vary with age classes. Within species, ...
and the inconspicuous locations they adopt are an effort to avoid predators and
mobbing Mobbing, as a sociological term, means bullying of an individual by a group, in any context, such as a family, peer group, school, workplace, neighborhood, community, or online. When it occurs as physical and emotional abuse in the workplace, suc ...
by small birds.


Communication

Owls, such as the eagle-owl, will use visual signaling in intraspecific communication (communication within the species), both in territorial habits and parent-offspring interactions. Some researchers believe owls can employ various visual signals in other situations involving intraspecific interaction. Experimental evidence suggests that owl feces and the remains of prey can act as visual signals. This new type of signaling behavior could potentially indicate the owls' current reproductive state to intruders, including other
territorial A territory is an area of land, sea, or space, particularly belonging or connected to a country, person, or animal. In international politics, a territory is usually either the total area from which a state may extract power resources or an ...
owls or non-breeding floaters. Feces are an ideal material for marking due to its minimal energetic costs, and can also continue to indicate territorial boundaries even when occupied in activities other than territorial defense. Preliminary evidence also suggests that owls will use feces and the feathers of their prey to signal their breeding status to members within the same species.


Migration

Some species of owl are migratory. One such species, the northern saw-whet owl, migrates south even when food and resources are ample in the north.


Habitat, climate and seasonal changes

Some owls have a higher survival rate and are more likely to reproduce in a habitat that contains a mixture of old growth forests and other vegetation types. Old growth forests provide ample dark areas for owls to hide from predators Like many organisms, spotted owls rely on forest fires to create their habitat and provide areas for foraging. Unfortunately, climate change and intentional fire suppression have altered natural fire habits. Owls avoid badly burned areas but they benefit from the mosaics of heterogeneous habitats created by fires. This is not to say that all fires are good for owls. Owls only thrive when fires are not of high severity and not large stand-replacing (high-severity fires that burn most of the vegetation) which create large canopy gaps that are not adequate for owls.


Parasites

Avian malaria or '' Plasmodium relictum'' affects owls and specifically, 44% of northern and Californian spotted owls harbor 17 strains of the parasite. As mentioned in the niche competition section above, spotted owls and barred owls are in competition so their niche overlap may be resulting in the plasmodium parasite having more hosts in a concentrated area but this is not certain.


Predators

The main predators of owls are other species of owls. An example of this occurs with the northern saw-whet owl that lives in the northern U.S. and lives low to the ground in brushy areas typically of cedar forests. These owls eat mice and perch in trees at eye level. Their main predators are barred owls and great horned owls.


Systematics

The family Strigidae was introduced by the English zoologist William Elford Leach in a guide to the contents of the
British Museum The British Museum is a public museum dedicated to human history, art and culture located in the Bloomsbury area of London. Its permanent collection of eight million works is among the largest and most comprehensive in existence. It documen ...
published in 1820. A
molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...
study of the owls published in 2019 found that the family Strigidae was divided into two sister clades and some of the traditional genera were paraphyletic. The placement of three monotypic genera remained uncertain due to the degraded nature of the available DNA. Based on these results
Frank Gill Frank Gill may refer to: * Frank Gill (Australian footballer) (1908–1970), Australian rules footballer with Carlton * Frank Gill (footballer, born 1948), footballer for Tranmere Rovers * Frank Gill (politician) (1917–1982), New Zealand politici ...
,
Pamela Rasmussen Pamela Cecile Rasmussen (born October 16, 1959) is an American ornithologist and expert on Asian birds. She was formerly a research associate at the Smithsonian Institution in Washington, D.C., and is based at the Michigan State University. She ...
and David Donsker updated the online list of world birds that they maintain on behalf of the International Ornithological Committee (IOC) but as currently defined '' Pseudoscops '' is embedded in ''
Asio ''Asio'' is a genus of typical owls, or true owls, in the family Strigidae. This group has representatives over most of the planet, and the short-eared owl is one of the most widespread of all bird species, breeding in Europe, Asia, North and ...
'' while '' Scotopelia '' and '' Ketupa'' are both embedded in ''
Bubo A bubo (Greek βουβών, ''boubṓn'', 'groin') is adenitis or inflammation of the lymph nodes and is an example of reactive lymphadenopathy. Classification Buboes are a symptom of bubonic plague and occur as painful swellings in the thighs ...
''. The above
cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...
is based on the results of a molecular phylogenetic study by Salter and collaborators published in 2019. The subfamilies are those defined by
Edward Dickinson Edward Dickinson (January 1, 1803 – June 16, 1874) was an American politician from Massachusetts. He is also known as the father of the poet Emily Dickinson; their family home in Amherst, the Dickinson Homestead, is a museum dedicated to her. ...
and James Van Remsen Jr. in 2013. The 235 extant or recently extinct
species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...
are assigned to 24 genera: * Genus ''
Uroglaux The Papuan hawk-owl (''Uroglaux dimorpha'') is a medium-sized, sleek owl with a proportionately small head, long tail, and short, rounded wings. Its white facial disk is small and indistinct, with black streaks, and white eyebrows. It has buff-co ...
'' – Papuan hawk-owl * Genus ''
Ninox ''Ninox'' is a genus of true owls comprising 36 species found in Asia and Australasia. Many species are known as hawk-owls or boobooks, but the northern hawk-owl (''Surnia ulula'') is not a member of this genus. Taxonomy The genus was introduce ...
'' – Australasian hawk-owls, 37 species of which one is recently extinct * Genus '' Margarobyas'' – bare-legged owl or Cuban screech-owl * Genus '' Taenioptynx'' – two species previous placed in ''Glaucidium'' * Genus '' Micrathene'' – elf owl * Genus '' Xenoglaux'' – long-whiskered owlet * Genus ''
Aegolius ''Aegolius'' is a genus of small true owls. The genus name is from Latin, ''aegolius'', is a type of screech owl that was thought to be a bird of ill omen. Taxonomy The genus ''Aegolius'' was introduced in 1829 by the German naturalist Johann J ...
'' – saw-whet owls, five species of which one is recently extinct * Genus '' Athene'' – nine species * Genus '' Surnia'' – northern hawk-owl * Genus '' Glaucidium'' – pygmy owls, 29 species * Genus ''
Otus Otus may refer to: * Otus (education), a K-12 educational technology company * HMS ''Otus'', two ships in the Royal Navy * ''Otus'' (bird), genus of owls * Otus (mythology), giant in Greek mythology, brother of Ephialtes, one of Aloadae * Otus ...
'' – scops owls, 58 species including three extinct species formerly placed in ''Mascarenotus'' * Genus '' Ptilopsis'' – white-faced owls, two species * Genus ''
Asio ''Asio'' is a genus of typical owls, or true owls, in the family Strigidae. This group has representatives over most of the planet, and the short-eared owl is one of the most widespread of all bird species, breeding in Europe, Asia, North and ...
'' – eared owls, nine species * Genus '' Jubula'' – maned owl * Genus ''
Bubo A bubo (Greek βουβών, ''boubṓn'', 'groin') is adenitis or inflammation of the lymph nodes and is an example of reactive lymphadenopathy. Classification Buboes are a symptom of bubonic plague and occur as painful swellings in the thighs ...
'' – horned owls, eagle-owls and fish-owls, 19 species * Genus ''
Scotopelia Fishing owls are a group of sub-Saharan African birds in the family Strigidae, the true owls. Fishing owls have traditionally been placed in the genus ''Scotopelia'', but DNA evidence suggests they should be included in genus ''Bubo A bubo (G ...
'' – three species embedded within ''Bubo'' * Genus '' Ketupa'' – three species embedded within ''Bubo'' * Genus '' Psiloscops'' – flammulated owl * Genus '' Gymnasio'' – Puerto Rican owl * Genus ''
Megascops Screech owls are typical owls (Strigidae) belonging to the genus ''Megascops'' with 23 living species. For most of the 20th century, this genus was merged with the Old World scops owls in ''Otus'', but nowadays it is again considered separate ...
'' – screech-owls, 25 species * Genus '' Pulsatrix'' – spectacled owls, three species * Genus '' Lophostrix'' – crested owl * Genus '' Strix'' – earless owls, 22 species, including four previously placed in ''Ciccaba''


Late Quaternary prehistoric extinctions

* Genus ''
Grallistrix The stilt-owls (''Grallistrix'') is an extinct genus of true owls which contains four species, all of which lived on the Hawaiian Islands. ''Grallistrix'' can be loosely translated as "owl on stilts". The genus received this name due to the lon ...
'' – stilt-owls, four species ** Kaua‘i stilt-owl, ''Grallistrix auceps'' ** Maui stilt-owl, ''Grallistrix erdmani'' ** Moloka‘i stilt-owl, ''Grallistrix geleches'' ** O‘ahu stilt-owl, ''Grallistrix orion'' * Genus '' Ornimegalonyx'' – Caribbean giant owls, one or two species ** Cuban giant owl, ''Ornimegalonyx oteroi'' **''Ornimegalonyx'' sp. – probably subspecies of ''O. oteroi'' * Genus ''
Asphaltoglaux The asphalt miniature owl (''Asphaltoglaux cecileae'') is an extinct species of true owl which existed in what is now California, U.S.A. during the Late Pleistocene epoch. The species is known from the La Brea Tar Pits. Its osteology suggests a ...
'' **
Asphalt miniature owl The asphalt miniature owl (''Asphaltoglaux cecileae'') is an extinct species of true owl which existed in what is now California, U.S.A. during the Late Pleistocene epoch. The species is known from the La Brea Tar Pits. Its osteology suggests a ...
, ''Asphaltoglaux cecileae'' *Genus '' Oraristrix'' ** La Brea owl, ''Oraristrix brea''


Fossil record

* '' Mioglaux'' (Late Oligocene? – Early Miocene of WC Europe) – includes ''"Bubo" poirreiri'' * '' Intulula'' (Early/Middle Miocene of WC Europe) – includes ''"Strix/Ninox" brevis'' * '' Alasio'' (Middle Miocene of Vieux-Collonges, France) – includes ''"Strix" collongensis'' The fossil database for Strigiformes is highly diverse and shows an origin from ~60MYA into the Pleistocene. The maximum age range for the Strigiformes clade extends to 68.6MYA. Placement unresolved: *''"Otus/Strix" wintershofensis'' – fossil (Early/Middle Miocene of Wintershof West, Germany) – may be close to extant genus ''Ninox'' * ''"Strix" edwardsi'' – fossil (Middle Miocene of Grive-Saint-Alban, France) * ''"Asio" pygmaeus'' – fossil (Early Pliocene of
Odessa Odesa (also spelled Odessa) is the third most populous city and municipality in Ukraine and a major seaport and transport hub located in the south-west of the country, on the northwestern shore of the Black Sea. The city is also the administrativ ...
, Ukraine) * Strigidae gen. et sp. indet. UMMP V31030 (Rexroad Late Pliocene of Kansas, USA) – ''Strix''/''Bubo''? *
Ibiza owl Ibiza (natively and officially in ca, Eivissa, ) is a Spanish island in the Mediterranean Sea off the eastern coast of the Iberian Peninsula. It is from the city of Valencia. It is the third largest of the Balearic Islands, in Spain. Its la ...
, Strigidae gen. et sp. indet. –
prehistoric Prehistory, also known as pre-literary history, is the period of human history between the use of the first stone tools by hominins 3.3 million years ago and the beginning of recorded history with the invention of writing systems. The use o ...
(Late Pleistocene/Holocene of Es Pouàs, Ibiza) The supposed fossil
heron The herons are long-legged, long-necked, freshwater and coastal birds in the family Ardeidae, with 72 recognised species, some of which are referred to as egrets or bitterns rather than herons. Members of the genera ''Botaurus'' and ''Ixobrychu ...
''"Ardea" lignitum'' (Late Pliocene of Germany) was apparently a strigid owl, possibly close to ''Bubo''.Olson, p. 167 The Early–Middle Eocene genus ''
Palaeoglaux ''Palaeoglaux'' is a genus of fossil owls from the Eocene epoch. The two known species are ''P. perrierensis'' from the Upper Eocene of Quercy, France, and ''P. artophoron'' from the Middle Eocene Messel shales, Germany.Mourer-Chauviré, Cécile ...
'' from west-central Europe is sometimes placed here, but given its age, it is probably better considered its own family for the time being.


References


Bibliography

*Olson, Storrs L. (1985). The fossil record of birds. ''In:'' Farner, D.S.; King, J.R. & Parkes, Kenneth C. (eds.): ''Avian Biology'' 8: 79–238. Academic Press, New York.


External links


ITIS – Strigidae TaxonomyTypical owl videos
on the Internet Bird Collection
The Owl Pages
about owls – photos, calls, books, art, mythology and more. {{Authority control Owls *