True owl

True owl

name = True owls

image_width = 200px
image_caption = Eastern Screech Owl
regnum = Animalia
phylum = Chordata
classis = Aves
ordo = Strigiformes
familia = Strigidae
familia_authority = Vigors, 1825
subdivision_ranks = Genera
subdivision = some 25, see text
synonyms =Striginae "sensu" Sibley & Ahlquist

True owls or typical owls (family Strigidae) are one of the two generally accepted families of owls, the other being the barn owls (Tytonidae). The Sibley-Ahlquist taxonomy unites the Caprimulgiformes with the owl order; here, the typical owls are a subfamily Striginae. This is unsupported by more recent research (see Cypselomorphae for details), but the relationships of the owls in general are still unresolved. This large family comprises around 189 living species in 25 genera. The typical owls have a cosmopolitan distribution and are found on every continent except Antarctica.


While typical owls (hereafter referred to simply as owls) vary greatly in size, with the smallest species, the Elf Owl, being a hundred times smaller than the largest, the Eurasian Eagle Owl, owls generally share an extremely similar body plan.J. S. Marks, R. J. Cannings & H. Mikkola (1999) "Family Strigidae (Typical Owls)". "In" del Hoyo, J.; Elliot, A. & Sargatal, J. (editors). (1999). "Handbook of the Birds of the World. Volume 5: Barn-Owls to Hummingbirds." Lynx Edicions. ISBN 8487334253 ] They tend to have large heads short tails, cryptic plumage and round facial discs around the eyes. The family is generally arboreal (with a few exceptions like the Burrowing Owl) and obtain their food on the wing. The wings are large, broad, rounded and long. Like other birds of prey many owl species exhibit reverse sexual dimorphism in size, where females are larger than males (as opposed to the more typical situation in birds where males are larger). [Caroline M. Earhart and Ned K. Johnson (1970) "Size Dimorphism and Food Habits of North American Owls" "Condor" 72 (3): 251-264]

Because of their nocturnal habits they tend not to exhibit sexual dimorphism in their plumage. The feathers are soft and the base of each is downy, allowing for silent flight. The toes and tarsus are feathered in some species, and more so in species at higher latitudes. [Kelso L & Kelso E (1936) "The Relation of Feathering of Feet of American Owls to Humidity of Environment and to Life Zones" "Auk" 53 (1): 51-56] Numerous species of owl 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 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 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 fine in the day.


Owls are generally nocturnal and spend much of the day roosting. They are often perceived as tame since they will allow people to approach quite closely before taking flight, but they are instead attempting to avoid detection. The cryptic plumage and inconspicuous locations adopted are an effort to avoid predators and mobbing by small birds.


The nearly 200 extant species are assigned to a number of genera, which are in taxonomic order:
* Genus "Megascops": screech-owls, some 20 species
* Genus "Otus": scops-owls; probably paraphyletic, about 45 species
* Genus "Pyrroglaux" - Palau Owl
* Genus "Gymnoglaux" - Bare-legged Owl or Cuban Screech-owl
* Genus "Ptilopsis" - white-faced owls, 2 species
* Genus "Mimizuku" - Giant Scops-owl or Mindanao Eagle-owl
* Genus "Bubo" - horned owls, eagle-owls and fish-owls; paraphyletic with "Nyctea", "Ketupa" and "Scotopelia", some 25 species
* Genus "Strix" - earless owls, some 15 species
* Genus "Ciccaba" - 4 species
* Genus "Lophostrix" - Crested Owl
* Genus "Jubula" - Maned Owl
* Genus "Pulsatrix" - spectacled owls, 3 species
* Genus "Surnia" - Northern Hawk-owl
* Genus "Glaucidium" - pygmy owls, about 30-35 species
* Genus "Xenoglaux" - Long-whiskered Owlet
* Genus "Micrathene" - Elf Owl
* Genus "Athene" - 2-4 species (depending on whether "Speotyto" and "Heteroglaux" are included or not)
* Genus "Aegolius" - saw-whet owls, 4 species
* Genus "Ninox" - Australasian hawk-owls, some 20 species
* Genus "Uroglaux" - Papuan Hawk-owl
* Genus "Pseudoscops" - Jamaican Owl and possibly Striped Owl
* Genus "Asio" - eared owls, 6-7 species
* Genus "Nesasio" - Fearful Owl

Recently extinct

* Genus "Mascarenotus" - Mascarene owls, 3 species (extinct c.1850)
* Genus "Sceloglaux" - Laughing Owl (extinct 1914?)

=Late Quaternary prehistoric extinctions=

* Genus "Grallistrix" - Stilt-owls, 4 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, 1-2 species
**Cuban Giant Owl, "Ornimegalonxy oteroi"
**"Ornimegalonyx" sp. - probably subspecies of "O. oteroi"

Fossil record

* "Mioglaux" (Late Oligocene? - Early Miocene of WC Europe) - includes "Bubo" poirreiri"
* "Intutula" (Early/Middle Miocene of WC Europe) - includes "Strix/Ninox" brevis"
* "Alasio" (Middle Miocene of Vieux-Collonges, France) - includes "Strix" collongensis"

Placement unresolved:
*"Otus/Strix" wintershofensis" - fossil (Early/Middle Miocene of Wintershof West, Germany) - may be close to extant genus "Ninox" (Olson 1985:131)
* "Strix" edwardsi" - fossil (Middle Miocene of Grive-Saint-Alban, France)
* "Asio" pygmaeus" - fossil (Early Pliocene of Odessa, Ukraine)
* Strigidae gen. et sp. indet. UMMP V31030 (Rexroad Late Pliocene of Kansas, USA) - "Strix"/"Bubo"? (Feduccia 1970)
*Ibiza Owl, Strigidae gen. et sp. indet. - prehistoric (Late Pleistocene/Holocene of Es Pouàs, Ibiza) - see Sánchez Marco 2004

The supposed fossil heron "Ardea" lignitum" (Late Pliocene of Germany) was apparently a strigid owl, possibly close to "Bubo" (Olson 1985:167). The Early - Middle Eocene genus "Palaeoglaux" from west-central Europe is sometimes placed here, but given its age it is probably better considered an own family for the time being.


* (1970): Some birds of prey from the Upper Pliocene of Kansas. "Auk" 87(4): 795-797. [ PDF fulltext]
* (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.
* (2004): Avian zoogeographical patterns during the Quaternary in the Mediterranean region and paleoclimatic interpretation. "Ardeola" 51(1): 91-132. [ PDF fulltext]

External links

* [ ITIS - Strigidae Taxonomy]
* [ Typical owl videos] on the Internet Bird Collection
* [ Strigidae sounds from the Neotropics] on
* [ The Owl Pages] about owls - photos, calls, books, art, mythology and more.

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