Owl

The Owls are the order Strigiformes, comprising 200 extant bird of prey species. Most are solitary, and nocturnal, with some exceptions (e.g. the Northern Hawk Owl). Owls hunt mostly small mammals, insects, and other birds, though a few species specialize in hunting fish. They are found in all regions of the Earth except Antarctica, most of Greenland, and some remote islands. Though owls are typically solitary, the literary collective noun for a group of owls is a parliament.

Living owls are divided into two families: the typical owls, Strigidae; and the barn-owls, Tytonidae.

Description

A little owl with its head completely facing the back.

Owls have 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. Although owls have binocular vision, their large eyes are fixed in their sockets, as with other birds, and they must turn their entire head to change views. Most birds of prey sport eyes on the sides of their heads, but the stereoscopic nature of the owl's forward-facing eyes permits a greater sense of depth perception necessary for low-light hunting.

Owls are farsighted and are unable to see anything clearly within a few centimeters of their eyes. Caught prey can be felt by owls with the use of filoplumes, which are small hair-like feathers on the beak and feet that act as "feelers". Their far vision, particularly in low light, is exceptionally good. Contrary to popular myth, an owl cannot turn its head completely backwards. It can turn its head 135 degrees in either direction; it can thus look behind its own shoulders, with a total 270-degree field of view.[1]

The smallest owl is the Elf Owl (Micrathene whitneyi), at as little as 31 g (1.1 oz) and 13.5cm (5.3 inches). Some of the pygmy owls are scarcely larger. The largest owls are two of the eagle owls; the Eurasian Eagle Owl (Bubo bubo) and Blakiston's Fish Owl (Bubo blakistoni)—which may reach a size of 60 - 71cm (28.4 in) long, have a wingspan of almost 2 m (6.6 ft), and an average weight of nearly 4.5kg (10 lb).

Eagle Owl

Different species of owls make different sounds; the wide range of calls aids owls in finding mates or announcing their presence to potential competitors, and also aids ornithologists and birders in locating these birds and recognizing species. The facial disc helps to funnel the sound of prey to their ears. In many species, these are placed asymmetrically, for better directional location.[2][verification needed]

The plumage of owls is generally cryptic, but many species have facial and head markings, including face masks, ear tufts and brightly coloured irises. These markings are generally more common in species inhabiting open habitats, and are thought to be used in signalling with other owls in low light conditions.[3]

Owl eggs are usually white and almost spherical, and range in number from a few to a dozen, depending on species. Eggs are laid at intervals of 1 to 3 days and do not hatch at the same time. This accounts for the wide variation in the size of sibling nestlings. Owls do not construct nests, but rather look for a sheltered nesting site or an abandoned nest in trees, underground burrows, or in buildings, barns and caves.
Behaviour

Most owls are nocturnal, actively hunting for prey only under the cover of darkness. Several types of owl, however, are crepuscular, active during the twilight hours of dawn and dusk; one example is the pygmy owl (Glaucidium). A few owls are also active during the day; examples are the Burrowing Owl (Speotyto cunicularia) and the Short-eared Owl (Asio flammeus).

The serrations on the leading edge of an owl's flight feathers reduce noise.

Much of the owls' hunting strategy depends on stealth and surprise. Owls have at least two adaptations that aid them in achieving stealth. First, the dull coloration of owls' feathers can render them almost invisible under certain conditions. Secondly, serrated edges on the leading edge owls' remiges muffle an owl's wingbeats, allowing its flight to be practically silent. Some fish-eating owls, for which silence is of no evolutionary advantage, lack this adaptation.

An owl's sharp beak and powerful talons allow it to kill its prey before swallowing it whole (unless it is too big). Scientists studying the diets of owls are helped by their habit of regurgitating the indigestible parts of their prey (such as bones, scales and fur) in the form of pellets. These "owl pellets", which are plentiful and easy to interpret, are often sold by companies to schools for dissection by students as a lesson in biology and ecology. [4]
Evolution and systematics

A Great Horned Owl (Bubo virginianus) sleeping at daytime in a hollow tree.

The systematic placement of owls is disputed. For example, the Sibley-Ahlquist taxonomy finds that, based on DNA-DNA hybridization, owls are more closely related to the nightjars and their allies (Caprimulgiformes) than to the diurnal predators in the order Falconiformes; consequently, the Caprimulgiformes are placed in the Strigiformes, and the owls in general become a family Strigidae. This is not supported by more recent research.[5] In any case, the relationships of the Caprimulgiformes, the owls, the falcons and the accipitrid raptors are not resolved to satisfaction; currently there is an increasing trend to consider each group (with the possible exception of the accipitrids) a distinct order.

There are some 220 to 225 extant species of owls, subdivided into two families: typical owls (Strigidae) and barn-owls (Tytonidae). Some entirely extinct families have also been erected based on fossil remains; these differ much from modern owls in being less specialized or specialized in a very different way (such as the terrestrial Sophiornithidae). The Paleocene genera Berruornis and Ogygoptynx show that owls were already present as a distinct lineage some 60 - 57 mya (million years ago), and presumably also some 5 million years earlier, at the extinction of the non-avian dinosaurs. This makes them one of the oldest known groups of non-Galloanserae landbirds. The supposed "Cretaceous owls" Bradycneme and Heptasteornis are apparently non-avialan maniraptors.[6]

During the Paleogene, the Strigiformes radiated into ecological niches now mostly filled by other groups of birds. The owls as we know them today, on the other hand, evolved their characteristic morphology and adaptations during that time, too. By the early Neogene, the other lineages had been displaced by other bird orders, leaving only barn-owls and typical owls. The latter at that time were usually a fairly generic type of (probably earless) owl similar to today's North American Spotted Owl or the European Tawny Owl; the diversity in size and ecology found in typical owls today developed only subsequently.

Around the Paleogene-Neogene boundary (some 25 mya), barn-owls were the dominant group of owls in southern Europe and adjacent Asia at least; the distribution of fossil and present-day owl lineages indicates that their decline is contemporary with the evolution of the different major lineages of typical owls, which for the most part seems to have taken place in Eurasia. In the Americas, there was rather an expansion of immigrant lineages of ancestral typical owls.

The supposed fossil herons "Ardea" perplexa (Middle Miocene of Sansan, France) and "Ardea" lignitum (Late Pliocene of Germany) were more probably owls; the latter was apparently close to the modern genus Bubo. Judging from this, the Late Miocene remains from France described as "Ardea" aureliensis should also be restudied.[7] The Messelasturidae, some of which were initially believed to be basal Strigiformes, are now generally accepted to be diurnal birds of prey showing some convergent evolution towards owls. The taxa often united under Strigogyps[8] were formerly placed in part with the owls, specifically the Sophiornithidae; they appear to be Ameghinornithidae instead.[9]

For fossil species and paleosubspecies of extant taxa, see the genus and species articles.

Unresolved and basal forms (all fossil)
Berruornis (Late Paleocene of France) - basal? Sophornithidae?
Strigiformes gen. et ap. indet. (Late Paleocene of Zhylga, Kazakhstan)
Palaeoglaux (Middle – Late Eocene of WC Europe) - own family Palaeoglaucidae or Strigidae?
Palaeobyas (Late Eocene/Early Oligocene of Quercy, France) - Tytonidae? Sophiornithidae?
Palaeotyto (Late Eocene/Early Oligocene of Quercy, France) - Tytonidae? Sophiornithidae?
Strigiformes gen. et spp. indet. (Early Oligocene of Wyoming, USA)[10]
Ogygoptyngidae
Ogygoptynx (Middle/Late Paleocene of Colorado, USA)
Protostrigidae
Eostrix (Early Eocene of WC USA and England - Middle Eocene of WC USA)
Minerva (Middle – Late Eocene of W USA) - formerly Protostrix, includes "Aquila" ferox, "Aquila" lydekkeri, and "Bubo" leptosteus
Oligostrix (mid-Oligocene of Saxony, Germany)
Sophiornithidae
Sophiornis
Strigidae: Typical owls

A Long-eared Owl, Asio otus, in erect pose
Aegolius: saw-whet owls, four species
Asio: eared owls, 6–7 species
Athene: 2–4 species (depending on whether Speotyto and Heteroglaux are included or not)
Bubo: horned owls, eagle-owls and fish-owls; paraphyletic with Nyctea, Ketupa and Scotopelia, some 25 species
Ciccaba: four species
Glaucidium: pygmy-owls, about 30–35 species
Gymnoglaux: Bare-legged Owl or Cuban Screech-owl
Jubula: Maned Owl
Lophostrix: Crested Owl
Megascops: screech-owls, some 20 species
Micrathene: Elf Owl
Mimizuku: Giant Scops-owl or Mindanao Eagle-owl
Ninox: Australasian hawk-owls, some 20 species
Nesasio - Fearful Owl
Otus: scops-owls; probably paraphyletic, about 45 species
Pseudoscops: Jamaican Owl and possibly Striped Owl
Ptilopsis: white-faced owls, two species
Pulsatrix: spectacled owls, three species
Pyrroglaux: Palau Owl
Strix: earless owls, about 15 species
Surnia: Northern Hawk-owl
Uroglaux: Papuan Hawk-owl
Xenoglaux: Long-whiskered Owlet
Mascarenotus: Mascarene owls, three species; extinct (c.1850)
Sceloglaux: Laughing Owl; extinct (1914?)
Grallistrix: stilt-owls, four species; prehistoric
Ornimegalonyx: Caribbean giant owls, 1–2 species; prehistoric

Fossil genera
Mioglaux (Late Oligocene? - Early Miocene of WC Europe) - includes "Bubo" poirreiri
"Otus/Strix" wintershofensis: fossil (Early/Middle Miocene of Wintershof West, Germany) - may be close to extant genus Ninox[10]
Intutula (Early/Middle –? Late Miocene of C Europe) - includes "Strix/Ninox" brevis
Alasio (Middle Miocene of Vieux-Collonges, France) - includes "Strix" collongensis

Placement unresolved

Masked Owl, Tyto novaehollandiae.
"Strix" edwardsi: fossil (Middle Miocene)
"Asio" pygmaeus: fossil (Early Pliocene of Odessa, Ukraine)
Ibiza Owl, Strigidae gen. et sp. indet.: prehistoric[11]
Tytonidae: Barn-owls
Genus Tyto: typical barn-owls, stand up to 1⁄2 feet (0.15 m) tall. Some 15 species and possibly one recently extinct
Genus Phodilus: bay-owls, 1–2 extant species and possibly one recently extinct

Fossil genera
Nocturnavis (Late Eocene/Early Oligocene) - includes "Bubo" incertus
Necrobyas (Late Eocene/Early Oligocene - Late Miocene) - includes "Bubo" arvernensis and Paratyto
Selenornis (Late Eocene/Early Oligocene) - includes "Asio" henrici
Prosybris (Early Oligocene? - Early Miocene)