Tytonidae

The bird family Tytonidae, which includes the barn owls Tyto and the bay owls Phodilus, is one of the two families of owls, the other being the true owls or typical owls, Strigidae. Tytonidae are medium to large owls with large heads and characteristic heart-shaped faces. They have long, strong legs with powerful talons. Tytonidae also differ from the Strigidae in structural details relating in particular to the sternum and feet.
The family is wide-ranging, although they are not very tolerant of severe winter cold, so are absent from northern areas of Europe, Asia, and North America; they are also absent from driest desert regions. They live in a wide range of habitats from semi-deserts to forests, and from temperate latitudes to the tropics. Within these habitats, they live near agricultural areas with high amounts of human activity. The majority of the 20 living species of barn owls are poorly known. Some, like the red owl, have barely been seen or studied since their discovery, in contrast to the western barn owl Tyto alba, which is one of the best-known owl species in the world. However, some subspecies of the western barn owl possibly deserve to be separate species, but are very poorly known.
Five species of barn owl are threatened, and some island species went extinct during the Holocene or earlier. Barn owls are mostly nocturnal and generally non-migratory, living in pairs or singly.

Taxonomy and systematics

Barn owls consist of two extant subfamilies: the Tytoninae or Tyto owls and the Phodilinae or bay owls. The modern genera Tyto and Phodilus are thought to have originated from a common ancestor from the Oligocene period. It is believed the modern genus Tyto descended from large nocturnal birds in the West Indies during the Quaternary. The systematics of this group began with the discovery of Tyto ostologa, whose remains were found in north-central Haiti. This discovery led to the finding of Tyto pollens, Tyto noeli, and Tyto riveroi in nearby cave deposits, all of which are now extinct and were also considered giant. The Sibley-Ahlquist taxonomy unites the Caprimulgiformes with the owl order; here, barn owls are a subfamily, Tytoninae. This is unsupported by more recent research, but the relationships of the owls in general are still unresolved.
The ashy-faced owl was for some time included in T. alba. Based on DNA evidence, König, Weick & Becking recognised the American barn owl and the Curaçao barn owl as separate species. They proposed that T. a. delicatula should be split off as a separate species, to be known as the eastern barn owl, which would include the subspecies T. d. delicatula, T. d. sumbaensis, T. d. meeki, T. d. crassirostris, and T. d. interposita. As of 2021, the International Ornithological Committee had not accepted the split of Tyto delicatula from T. javanica.
Some island subspecies are occasionally treated as distinct species, a move which should await further research into barn owl phylogeography. According to Murray Bruce in Handbook of Birds of the World Volume 5: Barn-owls to Hummingbirds, "a review of the whole group long overdue". Molecular analysis of mitochondrial DNA shows a separation of the species into two clades, an Old World alba and a New World furcata, but this study did not include T. a. delicatula, which the authors seem to have accepted as a separate species. Extensive genetic variation was found between the Indonesian T. a. stertens and other members of the alba clade, leading to the separation of stertens into Tyto javanica.
Twenty to thirty subspecies are usually recognized, varying mainly in body proportions, size, and colour. Barn owls range in colour from the almost beige-and-white nominate subspecies alba, erlangeri, and niveicauda, to the nearly black-and-brown contempta. Island forms are mostly smaller than mainland ones, and those inhabiting forests have darker plumage and shorter wings than those living in open grasslands. Several subspecies are generally considered to be intergrades between more distinct populations.

Extant genera

Two extant genera are accepted:

Genus Tyto – barn owls, grass owls and masked owls
Genus Phodilus – bay owls
Genus ''Tyto''

Some of the Tyto species that exist include the western barn owl, the American barn owl, and the eastern barn owl. Within each of these species, there are many subspecies. Of the western barn owl there are 10 subspecies: T. a. alba, T. a. detorta, T. a. erlangeri, T. a. ernesti, T. a. gracilirostris, T. a. guttata, T. a. hypermetra, T. a. poensis, T. a. schmitzi, T. a. thomensis. Of the American barn owl, there are 10 subspecies: T. f. bargei, T. f. bondi, T. f. contempta, T. f. furcata, T. f. guatemalae, T. f. hellmayri, T. f. niveicauda, T. f. pratincola, T. f. punctatissima, T. f. tuidara. Of the Australian barn owl, there are 7 subspecies: T. j. crassirostris, T. j. delicatula, T. j. javanica, T. j. interposita, T. j. meeki, T. j. stertens, T. j. sumbaensis.
The western barn owl can be found in Africa and parts of Asia, including Eurasia. The American barn owl can be found from North to South America. Lastly, the Australian barn owl can be found in Australia, New Zealand, Polynesia, and Asia.

Genus ''Phodilus''

This genus includes the Oriental bay owl and the Sri Lanka bay owl. The genus has a much smaller distribution than Tyto, with Oriental bay owls found in tropical Asia and Sri Lanka bay owls found in Sri Lanka and southwestern India.

Extinct genera

The fossil record of barn owls goes back to the Eocene, with the family eventually losing ground to the true owls after the radiation of rodents and owls during the Neogene epoch. Two subfamilies are known only from the fossil record: the Necrobyinae and the Selenornithinae. At least four extinct genera of barn owls have been described:

Genus Nocturnavis – includes Bubo incertus
Genus Necrobyas – includes Bubo arvernensis and Paratyto
Genus Selenornis – includes Asio henrici
Genus ''Prosybris''
Placement unresolved
Tytonidae gen. et sp. indet. "TMT 164" - Prosybris?
Genus Palaeotyto from Quercy, France. Placement in this family is tentative, it may instead belong to the family Sophiornithidae.
Genus Palaeobyas from Quercy, France. Placement in this family is tentative, it may instead belong to the family Sophiornithidae.
Former genera

The supposed "giant barn owl" Basityto from the Early Eocene of Grafenmühle was actually a crowned crane ; the presumed "Easter Island barn owl", based on subfossil bones found on Rapa Nui, has turned out to be a procellarid; and the specimen originally described as the fossilized Pliocene Lechusa stirtoni was later determined to be recent remains of a modern-day American barn owl.

Description

The main characteristic of the barn owls is the heart-shaped facial disc, formed by stiff feathers which serve to amplify and locate the source of sounds when hunting. Further adaptations in the wing feathers eliminate sound caused by flying, aiding both the hearing of the owl listening for hidden prey and keeping the prey unaware of the owl. Barn owls overall are darker on the back than the front, usually an orange-brown colour, the front being a paler version of the back or mottled, although considerable variation is seen even within species.
Bay owls closely resemble the Tyto owls, but have a divided facial disc, ear tufts, and tend to be smaller.

Distribution

The barn owl is the most widespread landbird species in the world, occurring on every continent except Antarctica. Its range includes all of Europe, most of Africa apart from the Sahara, the Indian subcontinent, Southeast Asia, Australia, many Pacific Islands, and North-, Central-, and South America. In general, it is considered to be sedentary, and, indeed, many individuals, having taken up residence in a particular location, remain there even when better nearby foraging areas are available. In the British Isles, the young seem largely to disperse along river corridors, and the distance travelled from their natal site averages about.
In continental Europe, the dispersal distance is greater, commonly somewhere between but exceptionally, with ringed birds from the Netherlands ending up in Spain and in Ukraine. In the United States, dispersal is typically over distances of, with the most travelled individuals ending up some from their points of origin. Dispersal movements in the African continent include, from Senegambia to Sierra Leone, and up to within South Africa. In Australia, there is some migration, as the birds move towards the northern coast in the dry season and southward in the wet season, as well as nomadic movements in association with rodent plagues. Occasionally, some of these birds turn up on Norfolk Island, Lord Howe Island, or New Zealand, showing that crossing the ocean is within their capabilities. In 2008, barn owls were recorded for the first time breeding in New Zealand. The barn owl has been successfully introduced into the Hawaiian island of Kauai in an attempt to control rodents; distressingly, it has been found to also feed on native birds.

Behaviour and ecology

Hunting and feeding

Hunting in twilight or at night, the barn owl can target its prey and dive to the ground. Its legs and toes are long and slender, which improves its ability to forage among dense foliage or beneath the snow and gives it a wide spread of talons when attacking prey. This bird hunts by flying slowly, quartering the ground and hovering over spots that may conceal prey. It has long, broad wings that enable it to manoeuvre and turn abruptly. It has acute hearing, with ears placed asymmetrically, which improves detection of sound position and distance; the bird does not require sight to hunt. The facial disc helps with the bird's hearing, as is shown by the fact that, with the ruff feathers removed, the bird can still determine a sound source's direction, although without the disc it cannot determine the source's height. It may perch on branches, fence posts, or other lookouts to scan its surroundings, and this is the main means of prey location in the oil palm plantations of Malaysia.
Rodents and other small mammals may constitute over ninety percent of the prey caught. Birds are also taken, as well as lizards, amphibians, fish, spiders, and insects. Even when they are plentiful, and other prey scarce, earthworms do not seem to be consumed. In North America and most of Europe, voles predominate in the diet, and shrews are the second most common food choice. In Ireland, the accidental introduction of the bank vole in the 1950s led to a major shift in the barn owl's diet: where their ranges overlap, the vole is now by far the largest prey item. Mice and rats are the main foodstuffs in the Mediterranean region, the tropics, subtropics, and Australia. Gophers, muskrats, hares, rabbits, and bats are also preyed upon. Barn owls are usually specialist feeders in productive areas and generalists in areas where prey is scarce.
On the Cape Verde Islands, geckos are the mainstay of the diet, supplemented by birds such as plovers, godwits, turnstones, weavers, and pratincoles. On a rocky islet off the coast of California, a clutch of four young were being reared on a diet of Leach's storm petrel. On bird-rich islands, a barn owl might include birds as some fifteen to twenty percent of its diet, while in grassland it will gorge itself on swarming termites, or on Orthoptera such as Copiphorinae katydids, Jerusalem crickets, or true crickets. Smaller prey is usually torn into chunks and eaten completely, including bones and fur, while prey larger than about —such as baby rabbits, Cryptomys blesmols, or Otomys vlei rats—is usually dismembered and the inedible parts discarded.
Compared to other owls of similar size, the barn owl has a much higher metabolic rate, requiring relatively more food. Relative to its size, barn owls consume more rodents. Studies have shown that an individual barn owl may eat one or more voles per night, equivalent to about fourteen percent of the bird's bodyweight. Excess food is often cached at roosting sites and can be used when food is scarce. This makes the barn owl one of the most economically valuable wildlife animals for agriculture. Farmers often find these owls more effective than poison in keeping down rodent pests, and they can encourage barn owl habitation by providing nesting sites.