[Animals] Owl - Description - Lifestyle

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Owls are birds from the order Strigiformes[1] (/ˈstrɪdʒəfɔːrmiːz/), which includes over 200 species of mostly solitary and nocturnal birds of prey typified by an upright stance, a large, broad head, binocular vision, binaural hearing, sharp talons, and feathers adapted for silent flight. Exceptions include the diurnal northern hawk-owl and the gregarious burrowing owl. Owls are divided into two families: the true (or typical) owl family, Strigidae, and the barn-owl family, Tytonidae.[2] Owls hunt mostly small mammals, insects, and other birds, although a few species specialize in hunting fish. They are found in all regions of the Earth except the polar ice caps and some remote islands. A group of owls is called a "parliament".[3] Anatomy 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 filoplumes—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 cutting off blood to the brain. Specifically, the foramina in their vertebrae through which the vertebral arteries pass are about 10 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 vertebrae higher than in other birds, giving the vessels some slack, and the 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.[4][5]

The smallest owl—weighing as little as 31 g (1+3⁄32 oz) and measuring some 13.5 cm (5+1⁄4 in)—is the elf owl (Micrathene whitneyi).[6] Around the same diminutive length, although slightly heavier, are the lesser known long-whiskered owlet (Xenoglaux loweryi) and Tamaulipas pygmy owl (Glaucidium sanchezi).[6] The largest owls are two similarly sized eagle owls; the Eurasian eagle-owl (Bubo bubo) and Blakiston's fish owl (Bubo blakistoni). The largest females of these species are 71 cm (28 in) long, have a 190 cm (75 in) wing span, and weigh 4.2 kg (9+1⁄4 lb).[6][7][8][9][10] 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 ornithologists and birders 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 cryptic, although several species have facial and head markings, including face masks, ear tufts, and brightly colored irises. 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.[11]


Sexual dimorphism USSR stamp, 1979 Sexual dimorphism is a physical difference between males and females of a species. Female owls are typically larger than the males.[12] The degree of size dimorphism varies across multiple populations and species, and is measured through various traits, such as wing span and body mass.[12] One theory suggests that selection has led males to be smaller because it allows them to be efficient 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.[13] If food is scarce, the male first feeds himself before feeding the female.[14] 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.[14] Furthermore, owls have been observed to be roughly the same size as their prey.[14] This has also been observed in other predatory birds,[13] 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] 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.[12] 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.[14] 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.[15] 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.[16]

https://en.wikipedia.org/wiki/Owl