Tawny Owl

] Adaptations to night vision include the large size of the eye, its tubular shape, large numbers of closely packed retinal rods, and an absence of cone cells, since colour vision is unnecessary at night. There are few coloured oil drops, which would reduce the light intensity.]

Geographical variation

Although both colour morphs occur in much of the European range, brown birds predominate in the more humid climate of western Europe, with the grey phase becoming more common further east; in the northernmost regions, all the owls are a cold-grey colour. Siberian and Central Asian subspecies have grey and white plumage, the North African race is dark grey-brown, and South and East Asian birds have barred, not striped, underparts, and fine lines around the facial disc. The Siberian and Scandinavian subspecies are 12% larger, 40% heavier, and have 13% longer wings than western European birds,cite book | last =Voous | first = Karel H. | coauthors= Cameron, Ad (illustrator) |title = Owls of the Northern Hemisphere| year = 1988 | publisher = London, Collins | isbn =0002194937|pages =209–219] in accordance with Bergmann's rule which predicts that northern forms will typically be bigger than their southern counterparts.de icon cite journal|last= Bergmann |first= Carl |year=1847 |title= Über die Verhältnisse der Wärmeökonomie der Thiere zu ihrer Grösse |journal= Göttinger Studien |volume= 3|issue=1 |pages= 595–708. |doi= ]

The plumage colour is genetically controlled, and studies in Finland and Italy indicate that grey morph Tawny Owls have more reproductive success, better immune resistance, and fewer parasites than brown birds. Although this might suggest that eventually the brown morph could disappear, the owls show no colour preference when choosing a mate, so the adverse selection pressure 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.cite journal|last= Brommer |first= Jon E. |coauthors= Kari, Ahola ; Karstinen, Teuvo |year=2005 |title= [http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1564093 The colour of fitness : plumage coloration and lifetime reproductive success in the tawny owl] |journal= Proceedings - Royal Society of London. Biological sciences |volume=272 |issue=1566 |pages=935–940 | doi =10.1098/rspb.2005.3052] cite journal|last= Galeotti |first= Paolo |coauthors= Sacchi, Roberto |year=2003 |title= Differential parasitaemia in the tawny owl ("Strix aluco"): effects of colour morph and habitat |journal= Journal of Zoology |volume=261 |pages= 91–99 | doi =10.1017/S0952836903003960]

Taxonomy

This species was first described by Linnaeus in his "Systema naturae" in 1758 under its current scientific name. [la icon cite book | last=Linnaeus | first=C | authorlink=Carolus Linnaeus | title=Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata. | publisher=Holmiae. (Laurentii Salvii). | year=1758| quote = S. capite laevi, corpore ferrugineo, iridíbus atris, remi-gibus primoribus serratís. |pages=93] The binomial derives from Greek "strix" "owl" and Italian "allocco", "Tawny Owl" (from Latin "ulucus" "screech-owl").cite web|title= Tawny Owl "Strix aluco" [Linnaeus, 1758] |work=BirdFacts |url= http://blx1.bto.org/birdfacts/results/bob7610.htm |publisher= British Trust for Ornithology (BTO) |accessdate=2008-05-31]

The Tawny Owl is a member of the wood-owl genus "Strix", part of the typical owl family Strigidae, which contains all species of owl other than the barn owls. Within its genus, the Tawny's closest relatives are Hume's Owl, "Strix butleri", (formerly considered to be conspecific), its larger northern neighbour, the Ural Owl, "S. uralensis", and the North American Barred Owl, "S. varia". The Early–Middle Pleistocene "Strix intermedia" is sometimes considered a paleosubspecies of the Tawny Owl, which would make it that species' immediate ancestor. [de icon Jánossy D. (1972) "Die mittelpleistozäne Vogelfauna der Stránská skála". In: Musil R. (ed.): "Stránská skála I." "Anthropos (Brno)" 20: 35–64.]

The Tawny Owl subspecies are often poorly differentiated, and may be at a flexible stage of subspecies formation with features related to the ambient temperature, the colour tone of the local habitat, and the size of available prey. Consequently, various authors have described between 10 and 15 subspecies. The currently recognised subspecies are listed below.cite web|title= Tawny Owl "Strix aluco" |work=Owl Information |url=http://www.owls.org/Species/strix/tawny_owl.htm |publisher= World Owl Trust |accessdate=2008-06-06]

Distribution and habitat

The Tawny Owl has a distribution stretching discontinuously across temperate Eurasia from Great Britain and the Iberian Peninsula eastwards to Korea, and south to Iran and the Himalayas. The subspecies "S. a. mauritanica" extends the range into northwest Africa. This essentially non-migratory owl is absent from Ireland, and only a rare vagrant to the Balearic and Canary Islands.

This species is found in deciduous and mixed forests, and sometimes mature conifer plantations, preferring locations with access to water. Cemeteries, gardens and parks have allowed it to spread into urban areas, including central London. The Tawny Owl is mainly a lowland bird in the colder parts of its range, but breeds to 550 m (1,800 ft) in Scotland, 1,600 m (5,250 ft) in the Alps, 2,350 m (7,700 ft) in Turkey, and up to 2,800 m (9,180 ft) in Burma.

The Tawny Owl has a geographical range of at least 10 million km² (3.8 million mi²) and a large population including an estimated 970,000–2,000,000 individuals in Europe alone. Population trends have not been quantified, but there is evidence of an overall increase. This owl is not believed to meet the IUCN Red List criterion of declining more than 30% in ten years or three generations and is therefore evaluated as Least Concern. This species has expanded its range in Belgium, the Netherlands, Norway and Ukraine, and populations are stable or increasing in most European countries. Declines have occurred in Finland, Estonia, Italy and Albania.cite book | last = Snow | first = David |coauthors= Perrins, Christopher M (editors)| title = The Birds of the Western Palearctic concise edition (2 volumes) | publisher = Oxford University Press |year = 1998| location =Oxford | isbn = 0-19-854099-X |pages = 907–910]

Behaviour

Breeding

Tawny Owls pair off from the age of one year, and stay together in a usually monogamous relationship for life. An established pair's territory is defended year-round and maintained with little, if any, boundary change from year to year. The pair sit in cover on a branch close to a tree trunk during the day, and usually roost separately from July to October. Roosting owls may be discovered and "mobbed" by small birds during the day, but they normally ignore the disturbance.

The Tawny Owl typically nests in a hole in a tree, but will also use old European Magpie nests, squirrel dreys or holes in buildings, and readily takes to nest boxes. It nests from February onwards in the south of its range, but rarely before mid-March in Scandinavia. The glossy white eggs are 48 x 39 mm (1.89 x 1.54 in) in size and weigh 39.0 g (1.4 oz) of which 7% is shell. The typical clutch of two or three eggs is incubated by the female alone for 30 days to hatching, and the altricial, downy chicks fledge in a further 35–39 days. The young usually leave the nest up to ten days before fledging, and hide on nearby branches.

This species is fearless in defence of its nest and young, and, like other "Strix" owls, strikes for the intruder's head with its sharp talons. Because its flight is silent, it may not be detected until it is too late to avoid the danger. Dogs, cats and humans may be assaulted, sometimes without provocation. Perhaps the best-known victim of the Tawny Owl's fierce attack was the renowned bird photographer Eric Hosking, who lost an eye when struck by a bird he was attempting to photograph near its nest. He later called his autobiography "An Eye for a Bird".cite book | last = Hosking | first = Eric | coauthors= Lane, Frank W. |title = An Eye for a Bird: The Autobiography of a Bird Photographer | year = 1972| publisher = London, Hutchinson & Co. |pages = 20 | isbn =009104460X ] The parents care for young birds for two or three months after they fledge, but from August to November the juveniles disperse to find a territory of their own to occupy. If they fail to find a vacant territory, they usually starve. The juvenile survival rate is unknown, but the annual survival rate for adults is 76.8%. The typical lifespan is 5 years, but an age of over 18 years has been recorded for a wild Tawny Owl, and of over 27 years for a captive bird.

Predators of the Tawny Owl include large birds such as Ural and Eagle Owls, Northern Goshawks and Common Buzzards. Pine Martens may raid nests, especially where artificial nest boxes make the owls easy to find, and several instances have been recorded of Eurasian Jackdaws building nests on top of a brooding female Tawny Owl leading to the death of the adult and chicks. A Danish study showed that predation by mammals, especially Red Foxes, was a important cause of mortality in newly fledged young, with 36% dying between fledging and independence. The mortality risk increased with fledging date from 14% in April to more than 58% in June, and increasing predation of late broods may be an important selective agent for early breeding in this species.cite journal|last= Sunde |first= Peter |month= September |year=2005 |title= Predators control post-fledging mortality in tawny owls, "Strix aluco". |journal= Oikos |volume= 110|issue=3 |pages=461–472, |doi= 10.1111/j.0030-1299.2005.14069.x ]

Feeding

The Tawny Owl hunts almost entirely at night, watching from a perch before dropping or gliding silently down to its victim, but very occasionally it will hunt in daylight when it has young to feed. This species takes a wide range of prey, mainly woodland rodents, but also other mammals up to the size of a young rabbit, and birds, earthworms and beetles. In urban areas, birds make up a larger proportion of the diet, and species as unlikely as Mallard and Kittiwake have been killed and eaten.

Prey is typically swallowed whole, with indigestible parts regurgitated as pellets. These are medium-sized and grey, consisting mainly of rodent fur and often with bones protruding, and are found in groups under trees used for roosting or nesting.cite book | last =Brown | first =Roy | coauthors= Ferguson, John; Lawrence, Michael; Lees, David |title = Tracks and Signs of the Birds of Britain and Europe (Helm Identification Guides)| year = 1987 | publisher = Christopher Helm | isbn = 0747002010 | pages = 86]

Less powerful woodland owls such as the Little Owl and the Long-eared Owl cannot usually co-exist with the stronger Tawny, which may take them as food items, and are found in different habitats. Similarly, where the Tawny Owl has moved into built-up areas, it tends to displace Barn Owls from their tradition nests sites in buildings.

In culture

The Tawny Owl, like its relatives, has often been seen as an omen of bad luck, and William Shakespeare used it as such in "Julius Caesar" (Act 1 Scene 3) "And yesterday the bird of night did sit/ Even at noon-day upon the market-place/ Hooting and shrieking." Even John Ruskin is quoted as saying "Whatever wise people may say of them, I at least have found the owl's cry always prophetic of mischief to me".cite book | last =Armstrong | first =Edward A. | title = The Folklore of Birds: An Enquiry into the Origin and Distribution of Some Magico-Religious Traditions | year = 1958 | publisher = London: Collins | pages =114| isbn = ]

Wordsworth described the technique for calling an owl in his poem "About a boy".cite book | last = Wordsworth, William | coauthors= Coleridge, Samuel Taylor |title = Lyrical Ballads | year = 1800 | publisher = London: Longman | isbn = ]

And there, with fingers interwoven, both hands
Pressed closely palm to palm and to his mouth
Uplifted, he, as through an instrument,
Blew mimic hootings to the silent owls,
That they might answer him.--And they would shout
Across the watery vale, and shout again,
Responsive to his call,--with quivering peals,
And long halloos, and screams, and echoes loud
Redoubled and redoubled; concourse wild
Of jocund din!

Owls were associated with Blodeuwedd, who betrayed Lleu Llaw Gyffes in the tale of Math son of Mathonwy from the ancient Welsh Mabinogion,cite web|title= Mab fab Mathonwy: The Mabinogi of Math |work= Fourth Branch of the Mabinogi |url= http://www.mabinogi.net/math.htm |accessdate=2008-06-06] and the call of an owl amongst the houses of a village was believed in Wales to signify that a girl had lost her virginity.cite web|title= Owls of the British Isles | date=2005-09-07|url=http://www.bbc.co.uk/dna/h2g2/A5104441 |publisher= BBC |accessdate=2008-06-06]

References

External links

* [http://www.arkive.org/species/ARK/birds/Strix_aluco/ ARKive - images and video of the Tawny Owl "(Strix aluco)"]
* [http://www.sovon.nl/ebcc/eoa/default.asp?species=7610 EBCC breeding map for Europe]