The tawny owl or brown owl (Strix aluco) is a stocky, medium-sized owl commonly found in woodlands across much of the Palearctic. The tawny owl is a member of the genus Strix, that is also the origin of the family's name under Linnaean taxonomy. Its underparts are pale with dark streaks, and the upperparts are either rufous, brown or grey. Several of the eight recognised subspecies have each of the main colour variations. This nocturnal bird of prey hunts a wide variety of prey species, but usually primarily takes small mammals such as rodents. Tawny owls usually hunt by dropping from a perch to seize their prey, which they typically swallow whole. In more urban areas, its diet includes a higher proportion of birds, while in arid subtropics many invertebrates such as insects are taken. Other important prey can include frogs with other vertebrate prey taken fairly rarely. Vision and well-developed hearing adaptations combined with silent flight aid its night hunting. The tawny owl is capable of catching smaller owls, but is itself vulnerable to larger raptors, like eagle-owls or goshawks. This species typically nests in a tree hollow, wherein they are likely to gain protection of their eggs and young against potential predators. The tawny owl is non-migratory and highly territorial. Many young birds starve if they cannot find a vacant territory once parental care ceases.Although many people believe this owl has exceptional night vision, its retina is no more sensitive than a human's and its asymmetrically placed ears are key to its hunting by giving it excellent directional hearing. Its nocturnal habits and eerie, easily imitated call, have led to a mythical association of the tawny owl with bad luck and death.

Description & appearance

This is a robust owl that is quite distinct for its large, rounded head. Tawny owls have no ear tufts but do possess a prominent facial disc rimmed in slightly dusky feathers. Despite having a broad facial disc rim, the facial disc is largely indistinct from the surrounding feathers in markings and colour, unlike some other owls that have relative bold facial disc patterns. The eyes are blackish-brown rimmed (at times imperceptibly) narrowly by the pale fleshy edges of the blue-grey eyelids. The underparts of all morphs are whitish in base colour. The underside feathers are barred in a dusky colour with several crossbars, producing a herringbone pattern.Their typical rich brownish colour often camouflages it well against a variety of woodland types. Tawny owls are spotted with white along the line of the scapulars, forming a white spotted "shoulder". The tail is rather short and the wings are broad. The tarsi and toes are densely feathered. Tawny owls possess relatively thick and heavy legs and feet and the talons are rather powerful and quite decurved. In flight they can appear fairly big and broad, large headed and rounded on the wings. The tawny owl often flies with long glides on rounded wings, less undulating and with fewer wingbeats than other Eurasian owls, and typically at a greater height.

The flight of the tawny owl is relatively heavy and slow, particularly at takeoff. They can appear to be a heavy flier but are capable of surprising maneuverability within woods, flying with utter silence. As with most owls, its flight is silent because of its feathers' soft, furry upper surfaces and a fringe on the leading edge of the outer primaries. Annual moult is usually complete in tawny owls but not all wing feathers are moulted each year. Feathers are moulted gradually between June and December. Of 91 males and 214 females in Great Britain, 17-19% did not moult any primaries, while 1-6% replaced all primaries, about 6% of males and 2% of females annually replaced median-primaries, while about 11% of males and 4% of females replaced annually their median secondaries. Young individuals can sometimes be diagnosed to age roughly by the state of wing moult. However, some variation in wing moult accounts for mistaken identification by age of 3 year old owls for younger ages due to the fact that they retain some worn juvenile wing feathers. Moult tends to occur after young fledge in late summer-early autumn for mature owls.

Plumage coloring in this species can be very variable. The nominate race in particular has two main morphs which differ in their plumage colour. The predominant morphs are grey and rufous, with a more minor intermediate or brown morph also sometimes occurring in various races; sometimes each morph may intergrade. The plumage colour is genetically controlled. There is some indication that pleiotropy has led to the colouring diversity in the species. Studies, largely based in Italy and in Finland, based on contour feathers indicate that grey morph owls are more densely insulated and better suited to surviving cooler conditions, which is roughly in keeping with the respective morph distribution. Meanwhile, in warmer and wetter and/or more humid conditions, rufous morph individuals are better adapted. However, similar studies on climate, habitat and colour morph found no strong correlation between colour morph, habitat and survivorship in Switzerland. Studies on colour morphs also indicated that higher levels of melanin, such as darker rufous morphs, may suffer higher rates of parasitism, body mass loss through the season across all ages but on the contrary also had higher growth rates for nestlings and were more likely to breed every year than grey morphs in Italy and Switzerland regardless of prey resources than grey morphs.

Studies in Finland indicate that grey morph tawny owls have more reproductive success, better immune resistance, and fewer parasites than other morphs. The data on grey morphs having the aforementioned advantages is also supported in Italian data. Although this might suggest that eventually the darker morphs could disappear, the owls show no colour preference when choosing a mate, so the selection pressure in favour of the grey morph is reduced. There are also environmental factors involved. The Italian study showed that brown-morph birds were found in denser woodland, and in Finland, Gloger's rule would suggest that paler birds would in any case predominate in the colder climate. In Poland, neither primary morph was necessary predominant, with 51.4% of 107 owls being rufous morph and 46.7% being grey morphs and this may qualify as a transitional zone. Other areas studied for colour morph proportions showed the following, in England (sample size 31): 55% rufous 39% grey and 6% intermediate; in France (315): 65% rufous and 35% grey; in Spain (54): 26% rufous, 65% grey and 9% intermediate; in Germany (50): 10% rufous and 90% grey; in Czech Republic (102): 32.3% rufous, 61.8% grey and 5.9% intermediate; Switzerland (79): 33% rufous and 67% grey.

Hearing is important for a nocturnal bird of prey, and as with other owls, the tawny owl's two ear openings differ in structure and are asymmetrically placed to improve directional hearing. A passage through the skull links the eardrums, and small differences in the time of arrival of a sound at each ear enables its source to be pinpointed. The left ear opening is higher on the head than the larger right ear and tilts downward, improving sensitivity to sounds from below. While the species does show the typical ear asymmetry of an owl and the right ear is consistently larger, the average differences of 7-13% are relatively modest for an owl. Both ear openings are hidden under the facial disk feathers, which are structurally specialized to be transparent to sound, and are supported by a movable fold of skin (the pre-aural flap). The ear slits average reportedly 21 to 23 mm (0.83 to 0.91 in) on the left and 22.5 to 26 mm (0.89 to 1.02 in) on the right. The movable pre-aural skin flap on tawny owl averages 9.5 mm (0.37 in) on the left and 10.5 mm (0.41 in) on the right. The tawny owls has a comparable ear morphology to the Ural owl (Strix uralensis). They tend to have a less complicated ear structure than those of Asio species but a more complicated, well-developed and relatively larger ear structure than those of other large generas of typical owl like the Bubo genus or Otus genus. The internal structure of the ear, which has large numbers of auditory neurons, gives an improved ability to detect low-frequency sounds at a distance, which could include rustling made by prey moving in vegetation. The tawny owl's hearing may be ten times better than a human's, and it can hunt using this sense alone in the dark of a woodland on an overcast night. However, the patter of raindrops can make it likely difficult for these owls to detect faint sounds, and prolonged wet weather, especially the crashing din of heavy rain, can lead to starvation if the owl cannot hunt effectively.The tawny's range is estimated to average 0.4-0.7 kHz with a maximum of around 3 kHz. The maximum range, in comparison, is up to 6 kHz in the long-eared owl and to 1 kHz in the eagle owl.

Voice, singing & call

Advertising calls and most threat and supplanting calls are mostly by males while both sexes may engage in contact calls and alarm calls.Autumn boundary disputes may occur with excited varied wails and screams between hoots (or "caterwauling"). The male has a quavering advertising song hoo...ho, ho, hoo-hoo-hoo-hoo or whooooh uk whooooook. It is described as “a clear, fluted, long-drawn hoot with a wailing quality”. Broken down, the male's song is considered as about three notes drawn together into one, often with an upward inflection and emphasis on the middle note, followed after a brief pause followed by a very short ho, uk or hu and continuing after a further short interval with a long tremolo of staccato notes, often rising or falling slightly in pitch and drawn out in the end. On average, the male's song is about 17 seconds in duration.The song may carry up to 1.5 to 2 km (0.93 to 1.24 mi) to human perception. More than 99% of the time, it was found that individual males could be distinguished via spectrogram in Italy. A female territorial call is somewhat like the male's but is hoarser, less clear and somewhat higher in pitch, transcribed as cher oooOOooo followed by chro cher-oooOOooo cooEEooooo. William Shakespeare used this owl's calls in Love's Labour's Lost (Act 5, Scene 2) as "Then nightly sings the staring owl, Tu-whit; Tu-who, a merry note, While greasy Joan doth keel the pot", but this stereotypical call is actually a duet, with the female making the kew-wick contact call. The male's response to the females kewick contact call is more varied, sometimes muffled and fluting notes, sometimes wavering or crooning notes and sometimes a more dissimilar hissing chruuuuuu.The calls of tawny owls are easily imitated by blowing into cupped hands through slightly parted thumbs, and a study in Cambridgeshire found that this mimicry produced a response from the owl within 30 minutes in 94% of trials. Recordings of various calls may also be an effective way for researchers to study territories and owl responsiveness. English male tawny owls were responsive both male and female calls, the latter perhaps due to an interest for mates, while females usually only responded to recordings of female calls.

Distribution & habitat

The preferred habitat of the tawny owl is temperate deciduous forest and mixed forest with some access to clearings. They too may habituate to riverine forests, parks, large gardens with old trees, open landscapes with wooded patches and avenues of trees in open agriculture. The species prefers "richly structured habitat" with old, mature trees available. Since they naturally tend to utilize tree hollows as nesting sites, sections of forest or woods with available snags may be ideal. They tend to occupy pure coniferous forest only near edges or when clearings and glades exist. Often areas in the conifer forest, especially the taiga in the north, where the tawnys will occur show a mixture of some deciduous tree growth such as birches and poplars. In the taiga-dominant environments of vast Russia, tawny owls are usually restricted to broadleaf stands often in river drainages, parks, orchards and cultivated lands, often where woods of Quercus, Tilia and Betula stand with plentiful broken snags and dead trees. Locally, the tawny owl has been known to be adaptive to subalpine forest dominated by conifers, such as the pine forests in the Spanish ranges of Sierra de Gredos and Sierra de Guadarrama. Similarly, in southern Poland, they reported occur in spruce-fir dominated forests. Also the species can habituate to rocky areas as long as they have scattered trees and bushes from which to execute hunting. Locally, tawny owls are quite adaptive to living near or in human settlements, extending to towns or cities, most often within timbered gardens or tree-line pavement areas.

They have adapted to living in parks or wooded suburban fringes of almost every major European city, including London and Berlin. They also live in and around even larger cities just outside of Europe, such as Istanbul and Moscow. Although tawny owls occur in urban environments, they are less likely to occur at sites with high noise levels at night. While this owl can settle in very young forest as long as nest boxes are available, woods with trees too young to support typical hunting behaviours from a prominent perch may be suboptimal. In Lithuania, it was found that nest boxes would booster the population in openings of the forest, interiors of mature forest and even grassland but no increase was noted in young forest in a state of recovery. In the well-studied population of Monks Wood, England, those living in more continuous sections of the woods (stands exceeding 4 ha (9.9 acres)) had more territorial skirmishes and overlapping territories while within farmland parts would be clustered around available wooded stands. In the Monks Woods, intermediate woods were probably preferable with less direct competition and more food was likely. In a Romanian study, tawny owls were rare in glades within the forest where substantial gaps occurred and were clustered around very old stands of trees, possibly being restricted from the more prey-rich glades by interspecific competition. In central Italy, 560 territories were studied in various habitats such as urban parks, mesophilic woods, sclerophyllous woods, and mountainous beech woods, with the most attractive and highest density type being in sclerophyllous woods and lowest in urban woods and mountainous beech. Generally, tawny owls occur in lowland areas but also may occur in mountainous areas (i.e. not exceeding 550 m (1,800 ft) in Scotland). They generally do not exceed 1,600 to 1,800 m (5,200 to 5,900 ft) above sea level in the Alps but may live at up to 2,650 m (8,690 ft) on Piz Lagrev in Switzerland. Tawny owls may live at elevations of over 2,000 m (6,600 ft) in parts of Armenia, Turkey and Tien Shen. The species may even occur at elevations of up to 4,200 m (13,800 ft) in the Himalayas.

Hunting & food

The tawny owl is an opportunistic and generalized predator. Peak hunting activity tends to occur largely between dusk to midnight, with owls often following an erratic hunting pattern, perhaps to sites where previous hunts were successful. When feeding young, hunting may need to be prolonged into daylight in the early morning. Based on hand-reared young owls that re-released into the wild, hunting behaviour is quite innate rather than learned. Normally this owl hunts from a perch. Perching bouts usually last from about 8 to 14 minutes depending largely on habitat.Tawny owl's hunting from a perch or pole can recall a buzzard and the two take similar prey sizes as well. However, high initial speed and maneuvering among trees and bushes with great dexterity may allow it to surprise relatively large prey, more like a goshawk. The tawny owl is capable of lifting and carrying off in flight individual prey weighing up to at least 320 g (11 oz). Their middle talon, the most enlarged claw on owls, measures an average of 19.1 mm (0.75 in). While not as large as those of the Ural owl, the talons are extremely sharp, stout and quite decurved. The claws are considered to be visibly more overdeveloped than those of other European mid-sized owls and the footspan including the claws is fairly larger as well, at an average of about 13.4 cm (5.3 in). The hunting owl often extends its wings to balance and control prey upon impact. Alternatively, this species may hunt from flight.

This occurs from 2 to 3 m (6.6 to 9.8 ft) over the ground, often over open habitats such as bushes, marsh or grassland, forming a quartering or zigzag pattern over the opening. During these flights they cover about 30 to 50 m (98 to 164 ft) before changing direction. Hunting from flight was surprisingly prevalent in a Swedish study of two radio-tagged birds, with 34% of study time spent hunting from flight while 40% of the study time was spent on hunting from a perch. In a similar study in England, less than 1% of time was spent hunting from flight. In a more deliberate variation of hunting from flight, the hunting owl may examine crags and nest boxes or also hover around prey roosts. In the latter type of hunts, the tawny owls may strike branches and/or beat their wings together in front of denser foliage, bushes or conifers in order to disturb and flush prey such as small birds and bats, or may dive directly into said foliage. Hovering has also been recorded in differing circumstances, including one incidence of an owl hunting a small bird that was caught on the wing after a hovering flight. Tawny owls have also taken bats on the wing as well (such as ones snatched from near streep lamps when attempting to hunt themselves) and have been seen to hawk large, relatively slow-flying insects such as some beetles and moths in flight. Caterpillars may too be taken from trees. Usually these hunting variations are correlated with poor weather hampering the capture of preferred prey. Tawny owls eat worms with relative frequency, as they often hear them apparently from below the surface and snatch them up from shallow dirt or below leaf litter. Their worm-hunting style recalls worm hunting techniques by most other birds and they were recorded to eat 0.39 worms per minute during an hour of observation in England and were sometimes seen to feed on worms during daylight. Other hunting from the ground has been observed, often of insects such as beetles, but tawny owls have also been reported to “leap” upon from a ground vantage point in order to capture a vole, quite like foxes often do. There are now many accounts of tawny owls feeding on carrion from a wide range of sources, including hares, rats, sheep, and trout.

Breeding & mating

Tawny owls are monogamous and territorial year around. Young birds select territories and look for mates in autumn and tend to be very vocal, especially males. Due to their highly territorial behaviour, young birds frequently struggle to establish a territory unless a nearby adult dies. Males routinely engage in territorial fights. Territories have been known to have been maintained by single tawnys for up to 10 years in Russia and 13 years in Berlin. Of 34 males in Wytham, only one male moved off of territory, due to being disturbed by humans. It appears to be largely up to the male to select territorial boundaries. Despite the aforementioned territorial behaviour, active nests of two separate pairs at as close as 100 m (330 ft), in the Tegel forest, have been reported. This species shows very little extrapair parentage. In Switzerland for example, a study of 137 nestings found that only one, or 0.7%, were from a different father than the mate, females cannot generally raise young without male contribution so the pair structure of these highly residential owls insures little instance of cuckoldry. Cases of bigamy were reported at Wytham in 6 of 34 males, in situations where apparently a neighboring male died and was suffixed subsequently, however, one or the other nesting attempts would completely fail each time. In Pavia, 3 of 22 territories included two mature females.

The male advertises several potential nest sites to his mate by singing at the entrance, slipping inside and so on, with the female finally selecting one. The typical nest site of a tawny owl is a tree hollow, wherein the owls will nest directly on the interior hole's surface. Tree hollows used may be as much as 25 m (82 ft) above the ground, but are usually within about 12 m (39 ft) of the ground. Virtually any species of deciduous tree may be used provided holes are available. These tree cavities may be of any origin, with trees that grow large such as oak, beech, poplar, maple, lime, hornbeam and alder often regularly utilized. Female may scratch out a shallow base in soil if present and sometimes seen to reportedly tear eggs into pieces as a cushion from their broods. Othe tree nest locations have included those on top of a Witch's broom and on top of the tree canopy. Natural holes in trees are often the most frequently used nesting site, followed closely in recent decades many artificial nest boxes, preferably those with a 15 cm × 20 cm (5.9 in × 7.9 in) entrance or larger. Of the nest boxes erected in different parts from Kielder forest and the Glenbranter forest of Argyll, 592 nest boxes were placed at 1.6 to 5.2 m (5.2 to 17.1 ft) high along the side of trees and 17.4% of which were used by tawnys (in latter 2 years of study up to 24.1%). In southeastern Scotland, all nest boxes erected in habitat were eventually utilized by tawny owls.

Many nest boxes were recorded to be used as roost sites in the Milan area, with only 12.3% of the 44% of nest boxes actually used by owls for breeding, usually with the owls utilizing boxes that were at least 6 m (20 ft) above the ground. Nest boxes are most successful wherever natural tree cavities are scarce or absent, such as conifer forests, young successional woods and farmlands. Tawny owls may not infrequently nest in an unmodified black woodpecker hole. This species may too nest in nest of larger birds such as crows, common ravens (Corvus corax) and Eurasian magpies as well as common buzzards, black kites, northern goshawks and various eagles while the sometimes recorded as used smaller nests such as those of Eurasian jays, Eurasian sparrowhawks and common wood pigeons but these are at potential risk of collapse. Occasionally, tawny owls have also been recorded nesting in abandoned burrows of larger mammals (e.g. red fox and European badger (Meles meles) as well as those of rabbits). Other nesting locations recorded for the species have included bare cliff ledges, between the roots of heavy tree trunks, on the bare forest floor and among heather. Also rarer still nests have been reported in the recesses of stone walls, in chimneys of large buildings, on cabins and sheds, in dovecotes and church towers. In southern Finland, 95% of 123 nest boxes put out were occupied by tawny owls in 1970–1975, natural tree hole use decreased in same period from 48% to 3%, on top of stumps from 4% to 1% and in buildings from 15% to 1%.

Chicks, juveniles & raise

Young begin to call in about 24 hours before they hatch. Asynchronous hatching occurs but is slightly less pronounced perhaps than long-eared and barn owls, rarely ranging up to 2–3 days apart.The female broods the owlets closely until 10–15 days, rarely ceasing as early as 7 days. In a Danish study, it was found that 59% of 268 nestlings were male, as opposed to roughly even sex ratio in Great Britain or Hungary, with the ratio not changing annually unlike clutch size, brood size and reproductive success. The gender of broods were studied relatively to testosterone levels in differently sized clutches in Hungary with smaller clutches with lower testosterone levels being male-biased. In this Hungarian study, survival rates were higher in smaller broods than in larger brood. Heavier parents raised all offspring hatched to them, while lighter parents raised 33% of the offspring. 59 of 99 reduced broods were males, while 34 of 81 unmodified broods male. Although sometimes said to only fed young at night, the mother can also parse out tiny bits of food by day to their nestlings. The young are fed small bits of meat for about 12 days, at which point the young open their eyes and begin to more actively beg. Also around 12 days, the nestlings produce their first pellets, though they are often of a rather liquid consistency. Older nestlings beg with quivering wings and intense high-pitched food begging calls. Female only regularly hunts again after brooding period (usually a little after the young are 2 weeks old). The male tends not to enter the nest to make food delivery, often the female receives it nearby on a branch of the tree or at the entrance of the nest hole, later when the nestlings are large, the male often will silently deposit the prey directly into the nest without landing.

When they are 21–25 days old, the young are stronger on their legs and feet and begin to spend much time around the entrance of the nest hole. Subsequently, they begin to emerge fully about 3–5 days later. It was found in warmer conditions, that the owlets born to rufous morph mothers requires less oxygen consumption and may experience lower stress levels during their early development. Evidently the oldest is usually the first to leave hole. After leaving the nest and becoming “branchers”, the young owls often clamber around using both the feet and the beak, and often land on the forest floor, from where they tend to flutter and climb into bushes, trying to reach higher parts of the trees (and should not be handled if found on the ground as such).Finally, at 29–37 days, with an average of 32.1 days in Kielder Forest, the young fledge, but take about another two weeks before they can fly strongly.The young post-fledgling owls continue to beg, often following and rarely leaving an area of about 50 m (160 ft) away from their mother.The pre-dispersal young used an area of 5 to 15 ha (12 to 37 acres) in England while, in Scotland, it was only 2.2 to 6.5 ha (5.4 to 16.1 acres). In Denmark, the distance between post-fledging siblings ranged from 11 to 0.6 m (36.1 to 2.0 ft) during day and 32 to 6 m (105 to 20 ft) by night, meaning that they are associative with one another at this stage, and they would spend 20-80% of nighttime hours food begging, up to 82% in poor food years. At around 1 to 3 months (sooner in Denmark, later in England on average), the young tawny owls begin to hunt for themselves. At the age of 2 to 3 months the young owls can be evicted by their parents, although often appear to disperse independently.However, on average of 72 radio-tagged juveniles in Denmark after the young owls would stop begging for food at 90–123 days of age, they would typically roost within their parents territories for another 18 days without incident. In the Danish Gribskov forest, 41 radio-tracked broods were dependent after fledging for a mean of 71 days (with a range of 56-84). 5 of 12 radiotagged juveniles survived dispersal in a different study from Denmark, independence was gained at an average 77.3 days and single day movements recorded of up to 4 km (2.5 mi). 22 radiotagged young tawny owls in England were tracked post-dispersal relative to vole concentrations, though there was no evidence that there were consistently able to access the peak vole areas. 27.4% of area selection was found to be likely correlated to vole access. The age at first breeding may be early as one year, but is more commonly 2–3 years old and rarely not until 4 years old.