Updated May 2014 apparently
Other common names: Barn Owl, Lesser Masked-owl(!), Monkey-faced Owl, Cave Owl, Death Owl, Delicate Owl, Demon Owl, Silver Owl, Ghost Owl, Golden Owl, Hissing Owl, Night Owl, Screech Owl, White Owl, Eastern Barn-owl (delicatula), Australian Barn-owl (delicatula), Galapagos Barn-owl (punctatissima) Taxonomy:
Strix alba
Scopoli, 1769, Friuli, Italy
Up to 46 races recognized in recent works, but status and distribution of several uncertain, and review of whole group long overdue. West Indian taxa glaucops, insularis and nigrescens formerly included in present species, now shown to represent a separate species, T. glaucops; some authors separate only glaucops, retaining other two races in present species. Considerable variation in size and colour may be more individual than geographical in many continental and some island regions, with possibly expanding zones of intergradation, particularly in Europe. Nominate and guttata intergrade from Netherlands, Belgium and N & E France E to Germany (Rhine Valley) and C Switzerland; nominate intergrades with affinis in region of S Egypt and N Sudan. Validity of many proposed races considered too doubtful to be upheld: in Europe, pusilla, kleinschmidti, kirchhoffi and hostilis merged with nominate, and rhenana with guttata; Madagascan hypermetra with African affinis; island populations everetti, kuehni, bellonae, lifuensis and lulu with widespread Australasian delicatula; Bahamian lucayana with pratincola; and, in Neotropics, Colombian subandeana with guatemalae, stictica with contempta, and hauchecornei with tuidara. Also, current separation of niveicauda from furcata (based on colour characters) and of guatemalae from pratincola (ranges in Central America not yet satisfactorily determined) perhaps doubtful, and continued separation of bondi may not be tenable; size and colour variation in Neotropics in need of reassessment, and separation of hellmayri from tuidara based on size characters questionable. Furthermore, poensis possibly not separable from affinis, in which case poensis (as older name) has priority over latter. N African birds of nominate race sometimes placed in erlangeri; birds from S Myanmar E to Indochina sometimes placed in javanica, but seem better included in stertens. Melanesian populations, currently covered by three races (delicatula, crassirostris, interposita), may merit further splits. Several well-marked insular races (e.g. detorta, thomensis, deroepstorffi, punctatissima and possibly others) may be separate species; recent proposals to elevate delicatula to species level, however, do not consider which races it would include. Twenty-eight subspecies currently recognized.
Subspecies and Distribution T. a. alba (Scopoli, 1769) - W & S Europe (including Balearic Is and Sicily) to N Turkey; also W Canary Is (Tenerife, Gran Canaria, El Hierro), and N Africa from Morocco to Egypt (except Sinai), S to N Mauritania, S Algeria, Niger (Aïr Massif) and NE Sudan. T. a. guttata (C. L. Brehm, 1831) - C Europe E to Latvia, Lithuania and Ukraine, and SE to Albania, Macedonia, Romainia and NE Greece. T. a. ernesti (Kleinschmidt, 1901) - Sardinia and Corsica. T. a. erlangeri W. L. Sclater, 1921 - Crete and smaller S Greek islands, Cyprus and patchily from Syria E to SW Iran and S to NE Egypt (Sinai) and S Arabian Peninsula. T. a. schmitzi (Hartert, 1900) - Madeira and Porto Santo. T. a. gracilirostris (Hartert, 1905) - E Canary Is (Fuerteventura, Lanzarote, Lobos, Montaña Clara, Alegranza). T. a. detorta Hartert, 1913 - Cape Verde Is. T. a. affinis (Blyth, 1862) - Africa S from S edge of Sahara, including Zanzibar and Pemba, and Madagascar and Comoro Is. T. a. poensis (Fraser, 1842) - Bioko I. T. a. thomensis (Hartlaub, 1852) - São Tomé I; recorded in error from Príncipe I. T. a. stertens Hartert, 1929 - Indian Subcontinent S to N Sri Lanka, and E to SC China (Yunnan), Vietnam and S Thailand. T. a. deroepstorffi (Hume, 1875) - S Andaman Is. T. a. javanica (J. F. Gmelin, 1788) - Malay Peninsula S to Greater Sundas (including Krakatau, Pulau Seribu and Kangean Is, and possibly S Borneo) and E to Alor, as well as Tanahjampea, Kalao and Kalaotoa. T. a. sumbaensis (Hartert, 1897) - Sumba I. T. a. meeki (Rothschild & Hartert, 1907) - E New Guinea and nearby islands of Manam and Karkar. T. a. delicatula (Gould, 1837) - Sawu, Roti(?), Timor, Jaco, Wetar, Kisar and Tanimbar Is; Australia and offshore islands; Long I and possibly N New Britain and New Ireland; also Nissan, Buka, Solomon Is (including Bougainville), S Vanuatu (Erromanga, Tanna, Aneityum), New Caledonia, Loyalty Is, Fiji (N to Rotuma), Tonga (N to Niafo’ou), Wallis and Futuna Is, Niue I, Western Samoa and Samoa. T. a. crassirostris Mayr, 1935 - Tanga Is (E Bismarck Archipelago). T. a. interposita Mayr, 1935 - Santa Cruz Is, Banks Is, N Vanuatu (S to Efate). T. a. pratincola (Bonaparte, 1838) - S Canada S at least to Mexico; also Bermuda, Bahamas and Hispaniola. T. a. guatemalae (Ridgway, 1874) - Guatemala and perhaps S Mexico to Panama (including Pearl Is), possibly to W Colombia. T. a. bondi Parkes & Phillips, 1978 - Bay Is (Roatán, Guanaja), off N Honduras. T. a. furcata (Temminck, 1827) - Cuba, Cayman Is and Jamaica. T. a. niveicauda Parkes & Phillips, 1978 - I of Pines. T. a. bargei (Hartert, 1892) - Curaçao, and possibly also Bonaire. T. a. punctatissima (G. R. Gray, 1838) - Galapagos Is. T. a. contempta (Hartert, 1898) - W Venezuela, Colombia (except W?), Ecuador and Peru. T. a. hellmayri Griscom & Greenway, 1937 - E Venezuela (including Margarita I) through the Guianas to N Brazil (S to Amazon); also Trinidad and Tobago. T. a. tuidara (J. E. Gray, 1829) - Brazil (S of Amazon) S to Tierra del Fuego and Falkland Is.
Introduced (affinis) to Seychelles; also (delicatula, pratincola) to Lord Howe I, where now presumed extirpated (few records since 1970s considered vagrants); also (pratincola) to Hawaii.
Descriptive notes
29–44 cm; 187–455 g (Europe, N Africa), 266–470 g (S Africa), 400–700 g (North America), 450–575 g (Cuba), 387–558 g (Suriname), 264 g (Galapagos Is); male av. 555 g, female av. 612 g (Malaysia); male 227–418 g, female 220–475 g (Australia). Medium-sized, long-legged owl with distinctive heart-shaped face. Nominate race is golden-buff above, with variable light greyish “veil”, and finely streaked, mottled and dotted dark; white facial disc and underparts, sometimes with pale buff on sides of chest and/or fine spotting on breast and flanks; legs densely feathered; eyes dark; buoyant, slow, wavering flight, with legs dangling, appears ghost-like. No similar owl over much of range (but in Afrotropics race affinis overlaps with T. capensis and from India E to Australia stertens and delicatula with T. longimembris, both those species longer-legged and usually notably darker, also in Australia with T. novaehollandiae, which usually larger and darker but some more like present species). Sexes similar, but female tends to be slightly darker than male. Juvenile is similar to adult, or more heavily spotted. Racial variation considerable, from light grey to buff above and from white to buff below, with varying amount of black spotting and speckling, but widespread intergradation (common in Europe and tropical regions), and island races tending to be smaller and with either whiter or buffier plumage (but some isolated, dark tropical island races): guttata is grey, sometimes buff-washed, above, buff (male) to rufous-buff (female) and usually spotted below; ernesti pale and white-breasted; erlangeri also white-breasted, but upperparts more golden; schmitzi, gracilirostris and detorta buff-breasted, darkest in detorta; affinis greyer above than nominate, with more and coarser spotting below; poensis similar, but darker above, more golden-buff and streaked and speckled black and white, primaries barred and tail buffier; thomensis smaller, much darker, dark grey above with conspicuous small black and white spots, golden-brown below; stertens pale and greyish above, with small spots on pale underparts; javanica similar but more golden-buff above, larger spots below; deroepstorffi smaller, darker, with dark brown upperparts, deep brownish-rufous underparts; sumbaensis slightly larger than javanica, larger bill, almost white tail with narrow black bars; meeki like sumbaensis but tail bars paler, bill smaller, underparts silvery white with arrow-shaped dusky spots; delicatula like javanica, but brownish-grey to light grey above, mottled pale brown with slight tawny tinge, white below, 4 brown bars on tail; crassirostris darker, bill and feet more robust; interposita washed orange-ochre; pratincola upperparts vary from pale orange-buff to lighter or darker grey mixed with orange-buff, underparts white to pale orange, spotted or vermiculated brown (similar to European birds but larger, with stronger legs and feet); guatemalae like darker pratincola, but more uniform above, more coarsely speckled below (extent of differentiation from pratincola indeterminate); bondi is apparently smaller and paler than pratincola; furcata pale orange-buff above with greyish-brown spots, white below with few flank spots; niveicauda is on average whiter and paler than furcata; bargei like nominate, but smaller, with shorter wings; punctatissima small, dull brown above with few scattered dusky white spots, golden-buff to white below with brownish vermiculations or fine dense spots; contempta black above with fine pale grey mottling and white spots at feather tips, pale rusty brown below with irregular black cross-markings, but characters variable; hellmayri larger than tuidara, both dark to pale yellowish above and near-white to golden-buff below, with or without dusky spotting.
Voice
Diverse range of calls associated with breeding, including screeches, wheezes, purrs, snores, twitters, hisses and yelps; less vocal at other times; also bill-snapping, tongue-clicking and wing-clapping. Male’s familiar screech, considered advertising or warning call, usually given in flight, a hoarse, screaming, eerie “shrrreeeeee” with gargling or rattling quality and tremulous effect (from wing action), of c. 2–3 seconds’ duration, repeated after 1–20 seconds, often many in series, but usually singly when patrolling territory; female’s variant is lower-pitched, more broken, especially when both sexes call during aerial chases. Variations of other loud screams and screeches attributed to mobbing response or distress behaviour. Habitat
Occurs in great variety of habitats according to availability of prey, seasonality in temperate regions, and competition from other predators; in higher latitudes limited by severity of winters, rarely occurring N of areas with mean Jan temperature around or few degrees below 0°C. Prefers open lowlands with some trees, including farmland with hedges, ditches, ponds and banks, roadside verges and related rougher terrain, and young conifer plantations; also around towns, suburbs, villages or more isolated buildings suitable for daytime roosts and nest-sites; sometimes near refuse dumps. In lower latitudes, also semi-arid and some arid regions with xerophytic vegetation, dwarf shrub and herb communities, deciduous or mixed eucalypt woodland, Acacia savanna, thornbush, heathland, open marshes, mudflats, oil palm (Elaeis guineensis) plantations, irrigation areas, rice paddies and cane fields, and cliffs and rocky coasts in some regions, notably on continental offshore islands; some darker island races also in forest; on small tropical islands in all available habitats. Usually lowlands, but in many areas also at higher altitudes, up to c. 4000 m. Food and feeding
Diet better studied than that of any other raptor, most extensively in Europe and North America but also in Israel, parts of Africa (particularly S Africa) and South America (Galapagos Is, Chile, Argentina, Suriname), Australia, and a few other localities. In major sample studies, 74–100% (in most cases 90–100%) of diet small mammals, usually dominated by only few species, especially rats and mice; in Europe and North America also voles (Cricetidae), gophers (Geomyidae) and shrews (Soricidae); in Africa also shrews, other Insectivora and gerbils (Gerbillinae); in South America also small opossums (Didelphidae); in Australia also bandicoots (Peramelidae), dasyurid marsupials and gliders (Burramyidae/Petauridae). Other mammals include young rabbits and hares (Leporidae), moles (Talpidae), bats, and skunks, stoats and weasels (Mustelidae). Also birds, particularly communally roosting passerines, e.g. thrushes (Turdidae), starlings (Sturnidae), sparrows (Passeridae), weavers (Ploceidae) and finches (Fringillidae), but vast range of other birds in small numbers or of local importance, from seabirds (Procellariidae, Hydrobatidae, Sternidae, Alcidae), small herons (Ardeidae), kestrels (Falco), young megapodes (Megapodidae), quails (Phasianidae), domestic fowl, buttonquails (Turnicidae), rails (Rallidae), plovers (Charadriidae) and small waders (Scolopacidae) to pigeons (Columbidae), lorikeets (Psittacidae), cuckoos (Cuculidae), swifts (Apodidae), kingfishers (Alcedinidae) and small woodpeckers (e.g. Colaptes), and wide range of passerines from at least 12 families. Other prey lacertid and agamid lizards, skinks (Scincidae), geckos (Gekkonidae), chameleons (Chamaeleonidae), slow-worms (Anguis fragilis) and grass snakes (Natrix natrix); frogs (Anura) and toads (Bufonidae); small fish, e.g. trout (Salmo), roach (Rutilus), carp (Cyprinidae), rudd (Scardinius erythrophthalmus), perch (Perca) and grunion (Leuresthes tenuis); larger insects, e.g. grasshoppers (Saltatoria), beetles (Coleoptera), mantises (Mantidae), moths (Lepidoptera), wasps (Hymenoptera) and termites (Isoptera); spiders (Arachnida) and scorpions (Scorpionida); littoral isopods (Isopoda); earthworms (Annelida); and rarely carrion. Much non-mammalian prey caught incidentally or opportunistically, but can constitute significant part of diet in some tropical and semi-arid regions, e.g. lizards and invertebrates in parts of Africa and on some islands. Discarded eggshells and faeces of smaller nestlings may also be eaten; occasional chick cannibalism at nest, victim usually dead from unknown causes, but young recorded killed and eaten by siblings. In some temperate regions, when main prey species scarce or absent, many starve rather than switch to alternatives; this occurs also in boom/bust cycle of rat and mouse plagues, when excess production of young leads to many often starving. Hunts close to ground in searching flight, undulating and hovering, diving on to prey with talons extended, usually from height of c. 3 m, also commonly from perch; either method used by same bird, or one more than other, depending on habitat type, e.g. perch-hunting predominant in denser vegetation. Normally strictly nocturnal, with high auditory acuity in locating prey in complete darkness. Daylight hunting regular in Scotland and England and well known on various Pacific islands; also observed elsewhere, e.g. W USA (Utah) and Suriname, though extent unknown; may be widespread if owls not mobbed when they appear. Normally hunts singly; sometimes many together during prey plagues, e.g. in Australia, where often joined by T. longimembris, T. novaehollandiae and other raptors.
Breeding
In tropics can start in almost any month, generally late in dry season, in more arid areas during wetter periods; in N temperate regions mostly Mar–Jun, when double-brooded mostly Mar–May and Jun–Aug, initial activity varying among habitats; in some temperate regions season correlated with cycles of prey abundance, but similar from year to year where highly dependent on more homogeneous agricultural landscapes; in South Africa after rains, Feb–May in summer-rainfall regions and Aug–Dec in winter-rainfall region of SW Cape, but can breed in any month depending on local conditions; in Australia opportunistic according to food supply, can be at any time of year, most peaking Mar–Jun and Aug–Nov; May–Aug in New Caledonia. One or two 2 broods, rarely three (e.g. in Malaysia), depending on food supply; exceptionally, four (Zimbabwe) within 11 months during mouse plague, with first egg of next clutch laid while chicks still in nest. Monogamous, but polygamy sometimes recorded, rarely polyandry and incest; territorial, but loosely colonial nesting recorded in USA; sometimes near other owls, e.g. in Scotland 34–40 m from Tawny Owl (Strix aluco) and in USA in association with Great Horned Owl (Bubo virginianus); in captivity, hybridization recorded between male of present species and a female Striped Owl (Asio clamator), 2 of 4 eggs fertile and developing until 15th day. Site a natural cavity in tree trunk, stump or large hollow branch, 2–20 m above ground, or in cliff or bank, including sea-cliffs and small, exposed islands, in cave, walls of lava tubes, even in ground; also in hollow of palm tree; wide diversity of artificial structures with adequate room and access also used (e.g. old church, tower, castle, ruin, barn, abandoned building, loft, dovecote, windmill, disused water tank, around bridges and other large structures, lighthouse, chimney, haystack, duckblind, unused boat, up to 10 m down in abandoned well); also purpose-built nestboxes and those used in rat-control programmes (e.g. in Malaysia); burrows c. 1 m deep in cliffs and banks may be wholly or partially excavated; also uses large abandoned nest, e.g. of Osprey (Pandion haliaetus), in Africa of Hamerkop (Scopus umbretta) and communal nests of Sociable Weaver (Philetairus socius); sometimes takes over occupied nest, e.g. in Scotland wool-lined stick nest of Eurasian Jackdaw (Corvus monedula) in chimney, yet recorded also as sharing active site with latter; some sites used over multiple seasons; either no nest or slight scrape or depression, with pellets and other debris as insulating layer. Clutch 2–16 eggs, usually 4–7, laid 2–3 or more days apart; if first clutch lost, replacement usually smaller; incubation period 29–34 days; male’s only involvement is in feeding female and young; natal down white, second (mesoptile) down white, creamy white or buffish-cream; nestling period 7–10 weeks; young dependent on parents for further 3–5 weeks, then disperse within 2–8 weeks. Most hatched chicks survive; in South Africa, record of 12 chicks successfully reared from a single nesting attempt. Can breed when less than 1 year old.
Movements
Most populations sedentary, with post-breeding dispersal of juveniles, as well as some movement of adults where prey numbers fluctuate. Data from Europe and North America indicate considerable regional variation, particularly after high prey abundance. In Scotland most disperse within 20 km; in C Europe 50–100+ km to W & S, with a few ringing recoveries 1200–1600 km distant; Dutch-ringed young moved c. 1500 km to Spain and Ukraine; nominate race vagrant in Azores, guttata on Jan–Mayen I and in S Scandinavia and S Finland, each also vagrant within other’s range. In America, pratincola from N USA move generally farther, 80–320 km, with recoveries at up to 1760 km; in S USA most disperse within 80 km, but recoveries at 248 km and 984 km indicate that wide dispersal not due entirely to severe winter weather; wanders or strays seasonally to Newfoundland, S Alaska, Tres Marías and Revillagigedo Is off W Mexico, Cuba, Hispaniola, Puerto Rico, Jamaica and Central America. Reported evidence of migration in NE USA suggested as flocking behaviour associated with post-breeding dispersal. Middle Eastern race erlangeri vagrant in NE Iran/Transcaspia region. Movements of Afrotropical affinis include 1000 km from Senegambia to Sierra Leone and 579 km and 400 km within S Africa. Indian/Indochinese race stertens may be merely vagrant in SC China (Yunnan), though recent sources suggest rare resident there; records from extreme S Thailand since 1970s may be N-moving javanica rather than stertens (javanica formerly only vagrant W of Java, with spread as breeding bird only since 1960s). Movements of 65–840 km recorded for delicatula in SE Australia, where some populations highly nomadic, with irruptions associated with rodent plagues, as well as seasonal movements to N areas for dry season (winter) and away from coasts in summer, doubtless accounting for long-distance vagrancy to Norfolk I and Lord Howe I and to New Zealand. Several New Zealand records, however, are of birds transported in undercarriage bays of aircraft (one, dead on arrival, apparently from USA), and some may originate from Fiji; the seven or eight records include one on Little Barrier I in Jun–Oct 1992. Race delicatula also irregular visitor to Tasmania and Bass Strait islands and vagrant to Houtman Abrolhos, off W Australia. In S South America tuidara has occasionally reached Falkland Is, where breeding first reported 1989; also on South Georgia, where evidence of breeding observed in 1998. Over-water dispersal is obvious source of many vagrants; several records of owls landing on ships up to 360 km from land suggest some vagrancy ship-assisted, e.g. a New Jersey bird recovered in Bermuda (c. 1250 km), where first bred 1931; also sightings on offshore oil rigs. In some tropical areas inter-island movement common, e.g. in smaller island groups of Fiji. Unidentified dark Tyto owls recently observed on several Fiji islands, if not vagrant T. longimembris, could be dark-morph birds of present species, hitherto unknown in Fiji.
Status and conservation
Not globally threatened. CITES II. Status of many populations uncertain, particularly those on islands, but others locally common; species expanding in some areas, especially temperate regions, as a result of increases in availability of suitable habitats and artificial nest-sites. Formerly occurred N to S Scandinavia, and small numbers have been reintroduced in S Finland; recently extinct in Malta, where last bred in 1988; has also disappeared from Aldabra; recorded in error from Austral Is and Society Is; recent breeding records in Falkland Is. Current European population 110,000–230,000 breeding pairs, with c. 90% of nominate race and two-thirds of total in just two countries (France and Spain); densities of up to c. 25 pairs/50 km² but generally much lower, especially in E Europe. Far greater densities attained in some nestbox programmes, e.g. on oil-palm estates in Malaysia: species first discovered nesting in Peninsular Malaysia in 1969 on an oil-palm estate, where many owls had been attracted to large population of rats feeding on oil palms; few nest-sites were available, but owls responded well when nestboxes provided; in 1988, attempt at biological control of rats, with 200 nestboxes erected for present species in 1000 ha of oil palms near Kuala Lumpur; by late 1989, 95% of boxes occupied, giving density of c. 1 pair/5 ha, and offering alternative to use of second-generation rodenticides; species now common throughout Malay Peninsula. Nestboxes used as part of local conservation efforts in Europe and North America, where N populations have been declining for c. 50 years; causes of decline include loss and fragmentation of grassland foraging habitat, intensification of agricultural practices since 1940s, urbanization, and road development, with attendant upsurge in road mortalities, all coupled with increasingly harsh winters during that period; not uncommonly a victim of road traffic, e.g. in systematic road surveys (conducted every two weeks, over a two-year period) of 248-km stretch of Interstate 84 in S Idaho, in W USA, total of 812 dead owls of present species were found, giving mortality rate of 1·64 owls/km/yr, which, after adjustment for search and removal bias, gave mortality of up to 5·99 owls/km/year. Increased mechanization of farms has meant loss of important foraging sites, such as stackyards and stables, and loss of abandoned farm buildings suitable for nest-sites. Organochlorine pesticides in 1950s and 1960s and rodenticides in 1970s and 1980s had disastrous effects on many owl populations in Europe, particularly NW Europe, and parts of North America; in NE Australia, rodenticides used since 1992 for rat control in cane fields have caused local population declines of 75–85%. Conservation efforts have also included protection and re-establishment of rough-grassland habitat mosaics, providing prey-rich foraging areas, and controls over use of second-generation anticoagulant rodenticides; reintroduction schemes in some areas have had mixed success, as well as conflicting with wild populations. While mortality rates in temperate regions can be very high, birds start breeding in first year, lay large clutches, young grow rapidly, and losses can quickly be replaced, so long as suitable habitat, prey abundance and nest-sites exist. Most die within 1–2 years, but ringing returns have demonstrated that small numbers survive for up to 21 years.