Tawny owl

Name and taxonomy

Carl Linnaeus named the species Strix aluco in 1758. Strix is the Greek word for an owl, and aluco comes from the Italian allocco. That Italian word traces back to a Latin name for a screech owl. The English name brown owl is still used, and wood owl describes the genus. Seven subspecies are now accepted, though authors have described between 10 and 15 over the years.

The subspecies are weakly marked and shade into one another. Their differences track local temperature, the colour of the woodland and the size of the local prey. That pattern suggests the species is still splitting rather than settled. Animal Diversity Web lists 11 races, which shows how far the authorities disagree.

Evolution and relatives

Strix is the genus of wood owls within the typical owl family Strigidae. That family holds every owl except the barn owls. The closest relatives are Hume's owl and the Himalayan owl, and both were once treated as the same species. The larger Ural owl is a northern neighbour and also a close relation. The barred owl of North America belongs to the same genus.

A fossil owl from the early and middle Pleistocene, Strix intermedia, may be its direct ancestor. In the Himalayas and East Asia the Himalayan owl takes its place. In northwest Africa the Maghreb owl fills the same role. Like other members of the genus, the tawny owl has dark eyes and no ear tufts.

Appearance

The tawny owl is 37 to 46 cm long and weighs 385 to 800 g. The wingspan is 81 to 105 cm, and the wings are broad and rounded. A male averages about 0.42 kg and a female about 0.52 kg. The female is roughly 5 per cent longer and more than 25 per cent heavier than her mate. The head is large and round, and there are no ear tufts at all.

The facial disc is plain and frames two dark brown eyes that look black. Pale crown stripes above the disc read as eyebrows and give the bird a mild face. The shoulder feathers carry a line of white spots, and the tail is finely barred. The underside is whitish with brown streaks in both colour forms. Young birds are paler than adults, and the moult runs from June to December.

The nominate race comes in two colour forms, one rufous brown and one greyish brown. Intermediate birds occur, and colour is under genetic control. Brown birds are commoner in the damp west of Europe and grey birds further east. In the far north every bird is a cold grey. Siberian and Scandinavian owls are 12 per cent larger and 40 per cent heavier than west European birds.

Habitat and range

The species is not migratory, and its range runs from Britain and Iberia east to western Siberia. It is missing from Ireland, probably because the long-eared owl holds the ground there. It turns up only as a rare stray in the Balearic and Canary Islands. The world range covers at least 10 million square kilometres. Europe alone may hold between one and two million birds.

Broadleaf and mixed woodland is the core habitat, and old oaks with wide holes are ideal. Mature conifer plantations are used, and water nearby is a strong preference. Cemeteries, parks and large gardens have carried the owl into towns, including central London. Urban birds avoid the noisiest sites, because a loud night blocks their hunting. Abandoned buildings and rock cavities serve as winter shelter.

In the cold north the tawny owl is a lowland bird. It breeds up to 550 metres in Scotland and 1600 m in the Alps. In Turkey it reaches 2350 m and in Myanmar 2800 m. The species has spread in Belgium, the Netherlands, Norway and Ukraine. It has declined in Finland, Estonia, Italy and Albania.

Diet and hunting

Woodland rodents make up most of the diet. Mice, voles and shrews are the staple, and a young rabbit is near the upper limit. Birds, frogs, earthworms and beetles fill the gaps when rodents are scarce. In towns birds take a much larger share of the diet. Urban owls have killed prey as unlikely as a mallard and a kittiwake. It also eats smaller owls, including the little owl and the long-eared owl.

Hunting runs from dusk to dawn, and a bird with young may work in daylight. The owl sits still on a perch, listens, then glides down without a sound. It spreads its wings over the victim and kills with its feet and claws. Now and then it strikes the base of the neck with its bill. It will also beat its wings at a bush to flush small birds and chase them in the air.

Prey goes down whole, and the bones and fur come back up as a pellet. The pellets are grey and medium-sized and gather under roost and nest trees. A heap of pellets probably records the whole diet of a pair for a season. Long spells of rain are the owl's worst enemy, because falling water masks the small sounds it hunts by. A wet week can leave a bird unable to feed itself.

Behaviour and social life

The tawny owl is nocturnal and spends the day perched close to a trunk in cover. Small birds sometimes find a roosting owl and mob it, and the owl usually ignores them. A pair roosts apart from July to October and together as winter comes on. The male sets the boundaries in October or November while the female looks for a hole. The pair then defends the same ground all through the winter and into spring.

Territory size follows the food supply. In thick woodland a pair may hold about 30 acres, and in open beechwood about 175 acres. In Norway, where prey is thin, territories average around 255 acres. Boundaries barely move from one year to the next. Rivals settle disputes by calling, by threat display, or by fighting in the air.

The owl defends its nest without fear and strikes at the head of an intruder. Because the flight makes no sound, the target rarely hears the attack coming. Dogs, cats and people have all been hit, sometimes with no warning. The photographer Eric Hosking lost his left eye to a tawny owl in 1937. He later titled his autobiography An Eye for a Bird.

Communication and senses

The male sings a quavering hoot that falls, pauses, and then runs into a shivering series. The female answers with a sharp kew-wick, and the two calls together make the familiar twit-twoo. Shakespeare wrote that pattern into Love's Labour's Lost as a single owl's song. Both sexes give a rippling trill during courtship, and young birds beg with a thin squeak. Males call more than females all year, and calling peaks during incubation.

A person can copy the hoot by blowing through cupped hands. In a Cambridgeshire study that trick drew a reply within half an hour in 94 per cent of tries. A male's answer also reports his condition, since sick birds use a narrower band of frequencies. Owls with heavy blood parasite loads drop the high notes from their reply.

The eyes face forward and their fields overlap by 50 to 70 per cent. That overlap beats the 30 to 50 per cent of daytime raptors and gives better depth judgement. The retina is packed with rod cells and carries almost no cones. The old claim of eyesight a hundred times better than ours is wrong, and the gain comes from the size and shape of the eye. The two ear openings differ in shape and sit at different heights on the skull. The tiny gap between the arrival of a sound at each ear fixes its direction, and the owl's hearing is ten times sharper than ours.

Reproduction and life cycle

Birds pair at one year old and usually stay together for life. A few males take more than one mate. Courtship centres on the future nest, where the male feeds the female. He sways on the branch, lifts each wing in turn, puffs his feathers and claps his wings. She replies with screeches and quivers with her own feathers raised.

The nest is a hole in a tree, and old magpie nests, squirrel dreys and buildings will do. The species takes readily to a nest box. Laying begins in February in the south and rarely before mid-March in Scandinavia. The clutch is normally two or three glossy white eggs, though 1 to 9 have been recorded. Each egg measures 48 by 39 mm and weighs 39 g, of which 7 per cent is shell.

The female alone incubates for about 30 days, and the male brings her food. The chicks hatch blind and downy and fledge 35 to 39 days later. They leave the hole up to ten days early and sit on branches nearby. Parents feed them for two or three months after they fly. Between August and November the young must find their own ground, and those that fail usually starve. The typical life is 5 years, and the oldest wild bird on record reached 22.4 years.

Predators and threats

Eagle owls, Ural owls, goshawks, buzzards and golden eagles all kill tawny owls. Pine martens raid nests, and a nest box in a town makes the raid easier. Jackdaws have built their own nests on top of a sitting female and killed her and her brood. A Danish study found that 36 per cent of fledglings died before they became independent. Red foxes and stone martens took most of them.

The danger to a fledgling grows through the season. It stood at 14 per cent in April and more than 58 per cent in June. That pressure probably explains why the species breeds so early in the year. Avian malaria is rising with the climate, and its rate has tripled in the last 70 years. A single degree Celsius of warming doubles or triples the infection rate. British owls stood at 60 per cent infected in 2010 against 2 to 3 per cent in 1996.

Population and conservation

The IUCN lists the tawny owl as Least Concern, and the world trend looks upward. The population is large, adaptable and locally very common. About 76.8 per cent of adults survive from one year to the next. Animal Diversity Web gives a lower adult figure of 73.8 per cent and 30.1 per cent for young birds. A captive bird has lived past 27 years.

The British picture is worse than the European one. The RSPB puts the British decline above 40 per cent between 1995 and 2023, and lists the owl as Amber. The Woodland Trust puts the drop at more than a third since the 1970s. Lost woodland and a shortage of old trees with holes are the likely causes. The species is listed on Appendix II of CITES, so trade in birds and parts is controlled.

Nest boxes help where old trees have gone, and the owl uses them readily. Boxes also expose broods to pine martens, so placement matters. A 2008 trial of hand-reared young found that 66 per cent lived beyond six weeks after release. Only 39 per cent were still alive a year later. The RSPCA judged that rate high enough to justify releasing rescued owlets.

Relationship with humans

The tawny owl lives closer to people than most owls. It breeds in city parks, churchyards and large gardens across Europe. Where it moves into a town it pushes barn owls out of their nest sites in buildings. It also eats mice and voles that damage crops and stores. Most people probably meet the bird only as a voice after dark.

The one real conflict is at the nest, where the owl attacks anything that comes near. At least two people in Britain have lost an eye to a strike. Photographers who work at a nest may wear a helmet and a face guard. Calling an owl in by imitating the hoot is a common British pastime. William Wordsworth described the trick in his poem There Was a Boy.

In culture and myth

The owl calls at night, and people across Europe read that voice as a warning. The species has long carried a name for bad luck and for death. Shakespeare used the bird as an omen in Julius Caesar, hooting in the market place at noon. John Ruskin wrote that an owl's cry always foretold trouble for him. The hoot is easy to copy, which probably helped the stories spread.

The best known owl sound in English is twit-twoo, and it belongs to this species. Most owls do not hoot at all, and many people expect them to. In English literary tradition, the staring owl of Love's Labour's Lost sings while the pot boils. In Roman tradition the Latin word behind aluco named a screeching night bird. In British folk practice, blowing through cupped hands calls the owl back to the caller.