Tytonidae

(vertebrate zoology) The barn owls, a family of birds in the order Strigiformes distinguished by an unnotched sternum which is fused to large clavicles.

(Tytonidae)

Class: Aves

Order: Strigiformes

Suborder: Strigi

Family: Tytonidae

Thumbnail description
Medium-sized owls with large head, dark eyes, heart-shaped facial disc, and with finely patterned plumage much like the wings of some moths

Size
9–22 in (23–57 cm)

Number of genera, species
2 genera; 17 species

Habitat
Most terrains, from forest to desert to urban areas, in cool temperate to tropical zones

Conservation status
Endangered: 3 species; Vulnerable: 1 species

Distribution
Almost worldwide

Evolution and systematics

Barn owls are represented in the fossil record back to the Paleocene (65 million years ago), along with at least four now-extinct owl families. The Tytonidae was most diverse through the Eocene, Oligocene, and Lower Miocene, with nine species in five genera, including two now-extinct subfamilies that shared characters of the extant genera Tyto and Phodilus. The highly diverse hawk owls (family Strigidae) arose by the Lower Miocene, and superseded the Tytonidae. The rise and diversification of owls have been linked to the tertiary radiation of small mammals.

Tyto owls appeared by the middle Miocene, and diversified through the Pliocene and Pleistocene. The now-extinct species were larger than modern Tyto, with some gigantic forms on islands. Some of these forms persisted until recent times (the Holocene Epoch). The common barn owl (Tyto alba) is known from the Pleistocene. The present center of diversity in the Australian region, with relict species in Africa, Madagascar, and Southeast Asia, suggests that the family originated in Gondwanaland.

Owls were formerly thought to be related to the diurnal birds of prey, order Falconiformes, but DNA comparisons have shown that they are instead related to the nightjars (Caprimulgiformes). Studies of anatomy, behavior, biochemistry, and genetics have shown that the barn owls, although closely related to the hawk owls (Strigidae), are distinct at the family level.

Barn owls, genus Tyto, and bay owls, genus Phodilus, are sufficiently different for separation into the subfamilies Tytoninae and Phodilinae. As of 2001, science recognizes 16 species in the genus Tyto, and one species in Phodilus, with a total of about 65 subspecies. Almost half of these are subspecies of the widespread common barn owl, which has many isolated populations on islands.

Physical characteristics

As noted by Iain Taylor in his book Barn Owls, published in 1994, these owls "when hunting over a meadow … have an ethereal quality that can be matched by no other bird." Barn owls are large-headed, short-tailed owls with a pale bill, and dark, frontally-set eyes in a flat, heart-shaped, prominently-rimmed facial disc. They range in size from 9–22 in (23–57 cm) and 0.4–2.8 lb (187–1,260 g). They are colored in browns and grays, often with a pale underside, and the dorsal plumage is intricately patterned in moth-like marbling, mottling, and flecking. The plumage is soft and fluffy, with flexible flight feathers in the large wings. Barn owls have a comb-like serration on the inner edge of the middle claw, absent in the Strigidae, but present in the nightjars. A nestling barn owl is characterized by its "long" face and bill, and emerging facial disc, and it develops extensive down that hides growing feathers. Other characteristics of barn owls which separate them from hawk owls include a tufted preen gland, primary feathers that are not narrowed at the tips or emarginated, an inner toe as long as the middle toe, and ear openings that are long slits covered by a flap of skin.

Distribution

Barn owls occur almost worldwide, being absent only from polar regions, the coldest parts of Eurasia and North America, and the driest Saharan and Middle Eastern deserts. The common barn owl is one of the most widely distributed land birds, being found on all continents except Antarctica as well as on many islands, although only vagrants have reached New Zealand. One species occurs in Europe, the Mediterranean, the Middle East, North America, and South America; three occur in Africa; two in Madagascar and the Caribbean; four in Southeast Asia; and 11 in Australasia. There are two endemic species in Africa, one each in Madagascar and the Caribbean, two in Southeast Asia, and nine in Australasia. Their current range is little changed from their historical range, except that the common barn owl has disappeared from southern Scandinavia, Malta, and Aldabra, and the eastern grass owl (Tyto longimembris) may be extinct in Fiji. The Australian masked owl (Tyto novaehollandiae) has become locally extinct in some agricultural parts of southern Australia.

Habitat

Barn owls inhabit forested, wooded, and open habitats from the tropics to the cool temperate zones. They reach their greatest diversity in the tropics and subtropics, where several species coexist by partitioning the habitat. In Australia the sooty owl (Tyto tenebricosa) and lesser sooty owl (T. multi-punctata) inhabit rainforest or moist hardwood forest with a rainforest understory, and take prey in trees and shrubs as well as on the ground. The Australian masked owl inhabits drier, more open and grassy forest or woodland, or limestone cave systems in treeless areas, and takes mainly terrestrial prey. The common barn owl inhabits open woodland, grassland, and urban areas, and takes small terrestrial prey. The eastern grass owl specializes in aerial foraging for terrestrial prey in rank grassland. In Southeast Asia the Oriental bay owl (Phodilus badius) inhabits rainforest. Similarly, the Itombwe owl (Tyto prigoginei) and the Madagascar red owl (T. soumagnei) inhabit rainforest, alongside the common barn owl and African grass owl (T. capensis) of open habitats. Barn owls roost in cavities such as tree hollows and caves, or in dense foliage, and nest in hollows or in caves, except for the grass owls which roost and nest on the ground in thick cover.

Behavior

Barn owls occur singly, in pairs, or in family groups consisting of the pair and recently fledged, dependent young. In times of abundant prey, the smaller species of open habitats may hunt and roost in loose aggregations. Barn owls roost alone, except during the courtship phase of the breeding cycle, when the male may roost with the female in a cavity that becomes the nest. On rousing at dusk, and through the night, they advertise or maintain contact with screeching, screaming, or whistling calls, unlike the hooting of hawk owls. At close range, they communicate with quieter trilling or chattering calls.

If cornered by a perceived enemy, barn owls bluff in a threat display of puffed-up plumage, outspread wings, swaying on their perch, loud snapping of the bill, and hissing or screeching. If pressed, they lunge with the bill, strike with a foot, or eject malodorous feces. The larger barn owls of forest and woodland, such as the sooty owl, are strongly territorial and defend large, exclusive home ranges. The smaller species, such as the common barn owl, are less territorial and defend only a small area immediately about the nest. Most territorial defense is vocal, but defenders will approach an intruder with the threat display, or even chase, grapple, and fight.

Barn owls usually sleep during the day, upright on one leg with the facial disc pinched into a triangular shape, and the closed wings hunched forward to hide most of the pale underside. They hunt through the night, often from a series of perches, but smaller species also hunt on the wing. During times of food shortage, the small species of open country will hunt on dull afternoons. They return to their roosts at dawn, sometimes calling from or near the roost.

Breeding adult barn owls behave as sedentary pairs occupying permanent home ranges. Newly independent juveniles disperse, moving in search of food or vacancies in the breeding population. After prolific breeding in good times, dispersing individuals of the smaller, open-country species are irruptive, occupying marginal habitats in numbers while conditions are favorable, and even breeding there. There may be mass starvation and death when conditions deteriorate, followed eventually by a new boom-and-bust cycle. Most juveniles disperse to within 30–60 mi (50–100 km) of their birth place, although some common barn owls and grass owls disperse hundreds of miles (kilometers).

Feeding ecology and diet

Barn owls prey on a variety of vertebrates and invertebrates, mainly small mammals supplemented by birds, reptiles, amphibians, and large insects. They specialize on rodents and rodent-like mammals such as shrews or small marsupials. They forage by watching and listening from a series of perches or, in the smaller species of open country, by aerial searching and hovering. They swoop to seize prey in the claws and kill it with a bite to the neck before plucking and dismembering it or, if the prey is small, swallowing it whole. Later, at the roost, they disgorge pellets of fur or feathers that contain the skulls and other bones of their prey. When fresh, the dried pellets of barn owls have a characteristically dark, "glazed" mucous coating.

Barn owls are highly specialized for detecting prey by sound, enabling them to make captures in total darkness even when they cannot see their targets. Acute directional hearing enables them to pinpoint the sounds of mammals rustling and squeaking, to within 1–2° in the horizontal and vertical planes. The facial disc acts as a parabolic dish for focusing and amplifying sounds, and channeling them to the asymmetrical ear openings that locate the source of sounds by parallaxis. Muscles behind the ears move the facial ruff, as if the intently listening owl is cupping its ears. Owls also have frayed edges to the flight feathers for silent flight, thus avoiding detection by their prey.

Reproductive biology

Courtship among barn owls is vocal and sometimes aerial. Male and female sooty owls engage in prolonged duets of trilling calls. Male Australian masked owls and eastern grass owls perform a prolonged circling and chattering or trilling flight, respectively. Male common barn owls screech incessantly and perform a hovering flight near the nest, and pursue the female about the site with chattering calls. Males of the well-known species also bring food to the female, which begs like a juvenile. Mating, preceded by twittering calls, courtship feeding, and mutual preening, takes place at or near the nest, and culminates with a squealing call. In the better-known species, the mating system is permanent monogamy for the life of either partner.

Barn owl eggs are white and rounded oval, and take around five weeks to hatch. The clutch size is from one or two in the sooty owls to seven or eight in the common barn owl and grass owls in good seasons. For most species the nest site is a natural or artificial cavity, such as a tree hole, but for the grass owls it is a tunnel and chamber within rank vegetation on the ground. Chicks hatch in sparse, pale down which is soon replaced by a thicker down. The growing feathers eventually show through as the down is shed, so that when fully fledged at around two months of age the owlets still have tufts of down on the head and thighs. By the time they leave the nest and fly, owlets are adult-sized but have shorter wings and tails because their flight feathers have not yet fully emerged from sheaths.

Incubation and brooding are undertaken solely by the female, which is fed on the nest by the male. The clutch is laid at two-day intervals and incubated from the start, so that eggs hatch sequentially and in a brood there is a range of ages. In times of food shortage, the youngest chicks may starve and be cannibalized. When the chicks are half-grown, feathering, and able to keep themselves warm, the female joins in providing for the family. Prey is at first dismembered and fed piecemeal to the chicks, but growing owlets are soon able to swallow whole surprisingly large items, such as rats. Fledged barn owls remain dependent on their parents for several weeks in small species to several months in large forest species, and can breed at one year of age.

In temperate regions barn owls lay in spring, and rarely manage more than one brood in a season. In warmer regions the laying season extends from autumn to spring, the onset of laying determined by food supply. In good years the smaller species of open habitats may raise two or three broods in succession, or even breed continuously during plagues of rodents.

Conservation status

Although barn owls are cryptic and under-recorded, several species such as the common barn owl, grass owls, sooty owl, and Australian masked owl are widespread and uncommon to locally common, or are common in a limited area (lesser sooty owl). Most are rarely encountered, endemic species with restricted ranges on small, tropical forested islands, particularly in Indonesia and Melanesia. Several are on the IUCN Red List. The Minahasa masked-owl (T. inexspectata) is listed as Vulnerable. The Madagascar red owl, the African bay owl (P. prigoginei), and the Taliabu masked owl (T. nigrobrunnea) are listed as Endangered. The lesser masked owl (T. sororcula) of the Moluccas, Sulawesi barn owl (T. rosenbergii), Andaman barn owl (T. deroepstorffi), and the ashy-faced owl (T. glaucops) of Caribbean islands, are also endemic species with highly restricted ranges. Two subspecies of the Australian masked owl were listed as Vulnerable on the Australian Environment Protection and Biodiversity Conservation Act 1999, but this situation was revised in 2000 to two subspecies classified as Near Threatened and two as Endangered.

Many members of the barn owl family have suffered population declines. The main reason is habitat loss: deforestation and logging in Australia and the tropics; conversion of natural grasslands to cultivation in the tropics and subtropics; and intensified agriculture in Western countries, with loss of foraging habitat and nest or roost sites. Rodenticides can also cause owl deaths. As of 2000, populations were estimated at 10,000 breeding individuals for the Australian subspecies of the sooty owl, a total of 21,300 for the Australian masked owl (all subspecies combined), and 10,000 for Australian populations of the eastern grass owl. In 1999, the European population of the common barn owl was estimated at 110,000–230,000 breeding pairs, meaning that its global population could be up to ten times that figure.

Significance to humans

Barn owls, by virtue of their nocturnal habits, ghostly appearance, eerie calls, and association with cemeteries and desolate places, have been featured in the mythology, literature, and art of all cultures since ancient times. As noted by Murray Bruce in Vol. 5 of the Handbook of the Birds of the World, "Few birds have accumulated such a wealth of varying and contradictory beliefs about them … [they are] feared or venerated, despised or admired, considered lucky or unlucky, and wise or foolish." They feature in superstitions concerning magic and witchcraft, prophecy, weather, birth, death, and other phenomena, and in potions, medicines, recipes, motifs, and the mummified contents of tombs. Common barn owls occasionally acquire a luminescent property to their plumage, which may contribute to the origin of legends concerning the "Will o' the wisp," "Jack o'lantern," and similar phenomena.

In modern times, barn owls have become popular as destroyers of rodent pests, and welcomed with the assistance of nest boxes in farm or town buildings. Common barn owls were introduced to some islands, with disastrous consequences for the endemic fauna. Barn owls are usually not dangerous to humans, although some individuals may defend owlets against human intruders at the nest by swooping and striking with their claws. The large species in Australia have become prominent in the debate over logging of old-growth forests.

Species accounts

Resources

del Hoyo, J., A. Elliott, and J. Sargatal, eds. Barn Owls to Hummingbirds. Vol. 5, Handbook of the Birds of the World. Barcelona: Lynx Edicions, 1999.

Garnett, S., and G. Crowley. The Action Plan for Australian Birds 2000. Canberra: Environment Australia, 2000.

Higgins, P. J., ed. Parrots to Dollarbird. Vol. 4, Handbook of Australian, New Zealand and Antarctic Birds. Melbourne: Oxford University Press, 1999.

König, C., F. Weick, and J.-H. Becking. Owls, A Guide to the Owls of the World. Mountfield, United Kingdom: Pica Press, 1999.

Taylor, I. Barn Owls: Predator-Prey Relationships and Conservation. Cambridge: Cambridge University Press, 1994.

Bellocq, M. I. "A Review of the Trophic Ecology of the Barn Owl in Argentina." Journal of Raptor Research 34 (2000): 425–434.

Debus, S. J. S. "Surveys of the Barking Owl and Masked Owl on the North-west Slopes of New South Wales." Corella 25 (2001): 5–11.

Debus, S. J. S., L. R. Agnew, and M. Schulz. "Surveys of the Grass Owl Tyto capensis in Coastal New South Wales." Australian Bird Watcher 19 (2001): 94–102.

Durant, J. M., and Y. Handrich. "Growth and Food Requirement Flexibility in Captive Chicks of the European Barn Owl (Tyto alba)." Journal of Zoology (London) 245 (1998): 137–145.

Fajardo, I. "Monitoring Non-Natural Mortality in the Barn Owl (Tyto alba) as an Indicator of Land Use and Social Awareness." Biological Conservation 97 (2001): 143–150.

Marti, C. D. "Natal and Breeding Dispersal in Barn Owls." Journal of Raptor Research 33 (1999): 181–189.

Massemin, S., and T. Zorn. "Highway Mortality of Barn Owls in Northeastern France." Journal of Raptor Research 32 (1998): 229–232.

McCafferty, D. J., J. B. Moncrieff, and I. R. Taylor. "How Much Energy Do Barn Owls (Tyto alba) Save by Roosting?" Journal of Thermal Biology 26 (2001): 193–203.

Mlikovsky, J. "A New Barn Owl (Aves, Strigidae) from the Early Miocene of Germany, with Comments on the Fossil History of the Tytoninae." Journal für Ornithologie 139 (1998): 247–261.

Ramsden, D. J. "Effect of Barn Conversion on Local Populations of Barn Owl Tyto alba." Bird Study 45 (1998): 68–76.

Roulin, A. "Nonrandom Pairing by Male Barn Owls Tyto alba with Respect to a Female Plumage Trait." Behavioural Ecology 18 (1999): 688–695.

Roulin, A., M. Köllicker, and H. Richner. "Barn Owl (Tyto alba) Siblings Vocally Negotiate Resources." Proceedings of the Royal Society of London B267 (2000): 459–463.

Tome, R., and J. Valkama. "Seasonal Variation in the Abundance and Habitat Use of Barn Owls Tyto alba on Lowland Farmland." Ornis Fennica 78 (2001): 109–118.

Walk, J. W., T. L. Esker, and S. A. Simpson. "Continuous Nesting of Barn Owls in Illinois." Wilson Bulletin 111 (1999): 572–573.

Australasian Raptor Association. 415 Riversdale Road, Hawthorn East, Victoria 3123 Australia. Phone: +61 3 98822622. Fax: +61 3 9882 2677. E-mail: mail@birdsaustralia.com.au Web site:

World Working Group on Birds of Prey and Owls. P.O. Box 52, Towcester, NN12 7ZW United Kingdom. Phone: +44 1 604 862 331. Fax: +44 1 604 862 331. E-mail: WWGBP@aol.com Web site:

[Article by: Stephen Debus, MSc]

The noun has one meaning:

Meaning #1: comprising only the barn owls
  Synonym: family Tytonidae

Barn-owls
Masked owl, Tyto novaehollandiae
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Aves Order: Strigiformes Family: Tytonidae Ridgway, 1914
Genera
Tyto Phodilus For fossil genera, see article.
Synonyms
Tytoninae sensu Sibley & Ahlquist

Barn-owls (family Tytonidae) are one of the two families of owls, the other being the typical owls, Strigidae. They are medium to large sized owls with large heads and characteristic heart-shaped faces. They have long strong legs with powerful talons. They also differ in structural details relating in particular to the sternum and feet.

The barn owls comprise two extant sub-families: the Tytoninae or Tyto owls (including the Common Barn Owl) and the Phodilinae or bay-owls. The Sibley-Ahlquist taxonomy unites the Caprimulgiformes with the owl order; here, the barn-owls are a subfamily Tytoninae. This is unsupported by more recent research^{[citation needed]}, but the relationships of the owls in general are still unresolved.

The barn owls are a wide ranging family, absent only from northern North America, Saharan Africa and large areas of Asia. They live in a wide range of habitats from deserts to forests, and from temperate latitudes to the tropics. The majority of the 16 living species of barn owls are poorly known. Some, like the Madagascar Red Owl, have barely been seen or studied since their discovery, in contrast to the Common Barn Owl, which is one of the best known owl species in the world. However, some sub-species of the Common Barn Owl possible deserve to be a species, and are very poorly known.

Five species of barn-owl are threatened, and some island species have gone extinct during the Holocene or earlier (e.g. Tyto pollens, known from the fossil record of Andros Island, and possibly the basis for the Chickcharnie). The barn-owls are mostly nocturnal, and generally non-migratory, living in pairs or singly.

Description

The barn-owls' main characteristic 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 there is considerable variation even amongst species. The bay-owls closely resemble the Tyto owls but have a divided facial disc, ear tufts, and tend to be smaller.

Species

The fossil record of the 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 only known from the fossil record, the Necrobyinae and the Selenornithinae. Numerous extinct species of Tyto have been described; see the genus page for more information.

Genus Tyto

Barn owl

• Greater Sooty-owl, T. tenebricosa
• Lesser Sooty-owl, T. multipunctata
• Australian Masked-owl, T. novaehollandiae
  • Cave-nesting Masked Owl, T. novaehollandiae troughtoni - disputed; probably extinct (1960s)
• Golden Masked-owl, T. aurantia
• Lesser Masked-owl, T. sororcula
  • Buru Masked-owl, T. (sororcula) cayelii - possibly extinct (mid-20th century?)
• Manus Masked-owl, T. manusi
• Taliabu Masked-owl, T. nigrobrunnea
• Minahassa Masked-owl, T. inexspectata
• Sulawesi Owl, T. rosenbergii
  • Peleng Masked Owl, T. rosenbergii pelengensis - probably extinct (mid-20th century)
• Barn Owl, T. alba
  • Eastern Barn Owl, T. (alba) delicatula
• Ashy-faced Owl, T. glaucops
• Madagascar Red Owl T. soumagnei
• African Grass-owl T. capensis
• Australasian Grass-owl T. longimembris

Genus Phodilus

• Oriental Bay-owl P. badius
  • Samar Bay-owl P. (badius) riverae - probably extinct (mid-20th century)
• Congo Bay-owl, P. prigoginei - sometimes placed in Tyto

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 of Quercy, France) - includes "Asio" henrici
• Prosybris (Late Eocene/Early Oligocene of Quercy? - Early Miocene of France)

Placement of the Late Eocene/Early Oligocene genera Palaeotyto and Palaeobyas from Quercy (France) in this family is tentative; they might belong to the Sophiornithidae instead.

The supposed "giant barn-owl" Basityto from the Early Eocene of Grafenmühle (Germany) was actually a crowned crane (Balearica); the presumed "Easter Island Barn-owl", based on subfossil bones found on Rapa Nui, has turned out to be some procellarid (Steadman, 2006).

References

• Bruce, M. D. (1999): Family Tytonidae (Barn-owls). In: del Hoyo, J.; Elliott, A. & Sargatal, J. (eds): Handbook of Birds of the World, Volume 5: Barn-owls to Hummingbirds: 34-75, plates 1-3. Lynx Edicions, Barcelona. ISBN 84-87334-25-3

• Steadman, David William (2006): Extinction and Biogeography of Tropical Pacific Islands Birds. University of Chicago Press. ISBN 0-226-77142-3.

External links

• Barn-Owls on the Internet Bird Collection

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