True owl

True owl or Typical owl (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 Strigidae. 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.

Morphology
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 and Blakiston's Fish Owl, owls generally share an extremely similar body plan. 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).

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. 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.

Behaviour
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.

Systematics
The nearly 200 extant species are assigned to a number of genera, which are in taxonomic order:

Ninoxinae: Hawk-owls

 * Genus Uroglaux - Papuan Hawk-owl
 * Genus Sceloglaux - Laughing Owl (extinct 1914?)
 * Genus Ninox - Australasian hawk-owls, some 20 species

Surniinae: Owlets and Pygmy-Owls

 * Genus Xenoglaux - Long-whiskered Owlet
 * Genus Micrathene - Elf Owl
 * Genus Aegolius - saw-whet owls, 4 species
 * Genus Heteroglaux - Forest Owlet
 * Genus Athene - 2 species
 * Genus Smithiglaux - 2 species
 * Genus Taenioglaux - 4 species
 * Genus Surnia - Northern Hawk-Owl
 * Genus Glaucidium - pygmy owls, about 30-35 species
 * Subgenus Phalaenopsis - 17 species

Otini: Scops-owls

 * Genus Pyrroglaux - Palau Owl
 * Genus Mascarenotus - Mascarene owls, 3 species (extinct c.1850)
 * Genus Otus: scops-owls; probably paraphyletic, about 45 species

Asionini: Eared Owls

 * Genus Ptilopsis - white-faced owls, 2 species
 * Genus Nesasio - Fearful Owl
 * Genus Asio - eared owls, 6-7 species

Megascopini: Screech-owls

 * Genus Psiloscops - Flammulated Owl
 * Genus Gymnoglaux - Bare-legged Owl or Cuban Screech-owl
 * Genus Megascops: screech-owls, some 20 species

Pulsatrigini

 * Genus Lophostrix - Crested Owl
 * Genus Pulsatrix - spectacled owls, 3 species

Strigini: Wood-owls

 * Genus Jubula - Maned Owl
 * Genus Strix - earless owls, some 10 species
 * Genus Ciccaba - split from Strix, 11 species

Bubonini: Eagle-owls

 * Genus Bubo - horned and eagle owls, some 10 species
 * Genus Nyctaetus - 2 species
 * Genus Scotopelia - 3 species
 * Genus Ketupa - 9 species

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 its own family for the time being.