Chouette de l'Oural

Identification

Like most Strix species, it has a broad, rounded head with a correspondingly round facial disc, barring a tiny V-shaped indentation. The Ural owl has, for an owl, an exceptionally long tail that bears a wedge-shaped tip. In colour, it tends to be a plain pale greyish-brown to whitish overall (with more detailed description of their variation under subspecies), with a slightly darker grey-brown to brown back and mantle with contrasting whitish markings. The underparts are pale cream-ochre to grey-brown and are boldly (though sometimes more subtly) overlaid with dark brown streaking, without crossbars. Many variations are known in overall plumage colour both at the subspecies level and the individual level. However, the Ural owl usually appears as a rather pale grey-brown owl, usually lacking in the warmer, richer colour tones of many other Strix owls, with distinct streaking below. In flight, a Ural owl shows a largely buffish-white underwing marked with heavy dark bars around the trailing edge and tip, while the long white tipped tail often appears slung downwards. Their flight style is reminiscent of a buzzard but with deeper, more relaxed wing beats, with their style of flight often giving the appearance of quite a large bird. The eyes are dark brown, being relatively small and closely set to each other, which is opined to give them a less “fierce” countenance than that of a great grey owl (Strix nebulosa). The eyes are reminiscent of an almond in both shape and colour. The bill is yellowish in colour, with a dirty yellow cere. Meanwhile, the tarsi and toes are covered in greyish feathering and the talons are yellowish brown with darker tips.<p>The Ural owl is a rather large species. Full-grown specimens range in total length from 50 to 64 cm (20 to 25 in), which may render them as roughly the eight longest owl species in the world (though many owls are heavier on average). Wingspan can vary in the species from 110 to 134 cm (3 ft 7 in to 4 ft 5 in). Like most birds of prey, the Ural owl displays reverse sexual dimorphism in size, with the female averaging slightly larger than the male. Reportedly talon size and body mass is the best way to distinguish the two sexes of Ural owl other than behavioral dichotomy based on observations in Finland. Weight is variable through the European part of the range. Males have been known to weigh from 451 to 1,050 g (0.994 to 2.315 lb) and females have been known to weigh from 569 to 1,454 g (1.254 to 3.206 lb). Voous estimated the typical weight of males and females at 720 g (1.59 lb) and 870 g (1.92 lb), respectively. It is one of the larger species in the Strix genus, being about 25% smaller overall than the great grey owl, the latter certainly being the largest of extant Strix species in every method of measurement. Body masses reported for some of the more southerly Asian species such as brown wood owl (Strix leptogrammica) and spotted wood owl (Strix selopato) (as well as the similarly sized but unweighed mottled wood owl (Strix ocellata)) show that they broadly overlap in body mass with the Ural owl or are even somewhat heavier typically despite being somewhat smaller in length, being somewhat stockier in build yet shorter tailed than the Ural owl. Despite having no published weights for adults, Père David's owl (Strix davidi) seems to also be of a similar size to the Ural owl as well. Among standard measurements, in both sexes, wing chord can measure from 267 to 400 mm (10.5 to 15.7 in) across the range and tail length can from 201 to 320 mm (7.9 to 12.6 in). Among extant owls, only the great grey owl is certain to have a longer tail. Though less frequently measured, the tarsus may range from 44 to 58.5 mm (1.73 to 2.30 in) and, in northern Europe, the total bill length measured from 38 to 45 mm (1.5 to 1.8 in). The foot span can regularly reach around 14.3 cm (5.6 in) in full-grown owls.<p>The song of the male is a deep rhythmic series of notes with a short pause after the first two notes, variously transcribed as wihu huw-huhuwo or huow-huow-huow. The phrase repeats at intervals of several seconds. The male's song may carry up to 2 km (1.2 mi) to human perception but usually is considered not quite that far-carrying. Peak singing times in Finland during springtime are 10 pm-12 am and more intensely at 1-3 am, which differed from the peak times for nest visits. The female has a similar but hoarser and slightly higher pitched song, giving it a more "barking" quality. Not infrequently, Ural owls will duet during courtship. In addition, a deep, hoarse heron-like kuwat or korrwick is probably used as a contact call. These are more elongated and harsher than the kewick note made by tawny owls (Strix aluco). Young beg with hoarse chrrreh calls, again similar to the ones by young tawny owls but deeper. Vocal behavior tends to peak in early spring until the young leave the nest, most often during incubation and nesting in the form of prey delivery countercalling. The alarm call, which is typically delivered during territorial rounds, of the male is coincidentally analogous to the territorial song of the short-eared owl (Asio flammeus), which is considered a somewhat hollow sounding hoot. The alarm call is audible at up to 1,500 m (4,900 ft) away. The Ural owl also has a particularly menacing bill-snapping display. In total, Swedish biologist reported that about nine different calls were uttered by Ural owls. Despite the range of calls, the species is generally very quiet for a large owl and may not vocalize even at peak times for perhaps up to nearly 2 days.<p>The ears of the Ural owl are quite large, averaging about 24 mm (0.94 in) on the left and 27 mm (1.1 in) on the right with the pre-aural dermal flap measuring about 13 mm (0.51 in). In fact their ears are amongst the largest recorded in owls. In combination with their large ears, the well-developed facial disc shows the importance of sound to hunting to this and other owl who hunt in boreal zones. While the Ural owl was found to be aurally overdeveloped compared to other Strix such as the barred owl (Strix varia) it was found to be underdeveloped in comparison to owls more confined to true boreal type habitats, like the great grey owl and the boreal owl (Aegolius funereus).<p>The Ural owl is a fairly distinctive looking bird but can be confused for other owls, especially with others in the Strix genus. The extralimital North American barred owl appears quite similar, the main feature differentiating the two being the Ural owl does not have concentric lines on its facial plate. The tawny owl is much smaller with a conspicuously shorter tail and a relatively larger head. The tawny species, which occurs variously in grey, brown and red morphs, has underparts with dark shaft-streaks and crossbars, as opposed to the heavy but straight streaking of the Ural owl. The great grey owl is larger than the Ural owl with a huge head and relatively even smaller yellow eyes while their facial disc has strong concentric lines. In colour, the great grey is distinctly more solidly uniform and somewhat dark greyish than the Ural owl. An unlikely species to mistake a Ural owl is the Eurasian eagle-owl (Bubo bubo) which is much larger (by a considerable margin the heaviest and longest winged owl in Europe) with prominent ear tufts, a squarish (not rounded) head shape and orange eyes as well as with distinctly different markings. Long-eared owls (Asio otus) are much smaller and slimmer, with prominent ear-tufts, orange eyes and more prominent dark markings. More similar than any in Europe, the closely related Père David's owl does not occur in the same range as (other?) Ural owls but is darker in plumage, also with a facial disc marked with darker concentric lines. Due to its partially diurnal behaviour during warmer months, some authors consider it confusable with the very different looking (but similarly largish and long-tailed) Eurasian goshawk (Accipiter gentilis).

Taxonomie

The Ural owl was named by Peter Simon Pallas in 1771 as Strix uralensis, due to the type specimen having been collected in the Ural mountains range. While the Urals fall around the middle of the species' distribution, some authors such as Karel Voous lamented that a more broadly appropriate than Ural owl was not derived for the English common name. In other languages, the species is referred to as Slaguggla, or “attacking owl”, in Swedish, Habichtskauz, or “goshawk-owl”, in German or as the “long-tailed owl” in Russian. The Ural owl is a member of the Strix genus, which are quite often referred to as wood owls. Conservatively, about 18 species are currently represented in this genus, typically being medium to large sized owls, characteristically round-headed and lacking ear tufts, which acclimate to living in forested parts of various climatic zones. Four owls native to the neotropics are sometimes additionally included with the Strix genus but some authorities have also included these in a separate but related genus, Ciccaba. Strix owls have an extensive fossil record and have long been widely distributed. The genetic relationship of true owls is somewhat muddled and different genetic testings has variously indicated that Strix owls are related to disparate appearing genera like Pulsatrix, Bubo and Asio.<p>The tawny owl is thought to be a close relative of the Ural owl. Authors have hypothesized that the origin of the species divide followed Pleistocene continental glaciations segregated a southwest or southern group in temperate forest (i.e. the tawny) from an eastern one inhabiting cold, boreal ranges (i.e. the Ural). The species pattern is mirrored in other bird species, i.e. the European green woodpecker (Picus viridus) from the more northern transcontinental grey-headed woodpecker (Picus canus). After retreat of the continental ice masses, the ranges more recently penetrated each other. While the life history details of the tawny and Ural owls are largely corresponding, nonetheless the species have a number of morphological differences and are largely adapted to different climates, times of activity and habitats. Based on Strix fossil species from Middle Pleistocene (given the name Strix intermedia) in variously the Czech Republic, Austria and Hungary show from leg and wing bones indicate an animal of intermediate form and size between Ural and tawny owls. However, fossils of a larger and differently proportioned Strix owl than a tawny owl, identified as Strix brevis, from Germany and Hungary from before the Pleistocene (i.e. Piacenzian) and as well as diagnosed Ural owl fossils from disparate southerly deposits in Sardinia from the Early Pleistocene and in Middle Pleistocene deposits in the Pannonian Basin as well as much later during the early Holocene from far to the west in Belgium, France and Switzerland suggest a more complicated evolutionary and distributional history. A hybrid was recorded in captivity between a male Ural and a female tawny owl, which managed to produce two offspring that were intermediate in size and had a more complex song that was also shared some characteristics with both species' vocalizations.<p>Some species in America, such as namely the barred owl, are at times thought to be so closely related as well to the extreme that the Ural and barred and spotted owls (Strix occidentalis), have been considered to potentially be part of a species complex or even within the same species. However, there is no evidence nor likelihood that the Strix owls between America and Eurasia ever formed a continuous population given their adaptation to well-forested areas as well as the fact that the barred owl is more ecologically similar to the more generalized tawny owl, despite being of intermediate size between tawny and Ural owls (closer in size to the latter), and that the tawny does not range anywhere close to the boundary between North America and Russia as does the Ural. Certainly the most ambiguous aspect of the relations of Ural owl is the Père David's owl which has both historically and currently been considered either an isolated subspecies of the Ural owl or a distinct species. It is thought that the Père David's is likely a glacial relict of the mountainous forest of western China where plant and animal life often remain reminiscent of pre-glacial life. Recent study has indicated that the Père David's owl is valid species based on appearance, voice, and life history differences, though genetic studies have shown a somewhat muddled diversity between races of the Ural owls species complex. It has been recognized by The Clements Checklist of Birds of the World but BirdLife International and IUCN still classify it as a subspecies of the Ural owl.<p>At least as many as 15 subspecies have been recognized by some authorities though some feel that there may be as few eight valid subspecies. Study of the phylogeographic genetics of Ural owls in Europe showed that they occur in about 5 distinct genetic clusters that do not correspond as well as expected to subspecies, and further that genetic exchange is considerable where subspecies ranges abut. The phylogeographic data indicates a continuous population in not the too distant history and discredits general classification of the species as a glacial relict, with isolation of populations likely being largely related to human interference.

Nom scientifique

Strix uralensis

Autorité

Pallas, 1771

Ordre

Strigiformes

Famille

Strigidae

Genre

Strix

Répartition et habitat

The Ural owl has a large distribution. In mainland Europe, its modern distribution is quite spotty, with the species being found in central Europe in southeastern Germany, central and eastern areas of the Czech Republic, southern Austria, all but western Slovenia, and spottily but broadly in several areas of western, southern and northeastern Poland. The distribution in Germany is particularly nebulous (and perhaps aided by reintroductions branching from the well-known Bavarian population), with evidence of Ural owls apparently residing (and possibly nesting) considerably away from currently known haunts in Egge far to the west and mysteriously turning up rather to the north in Harz and Lüneburg Heath. In eastern Europe, the species is found in eastern Croatia, Bosnia and Herzegovina, western Serbia, montane west-central Bulgaria, montane central Romania, much of Slovakia, southwestern Ukraine, southern and eastern Lithuania, northern Belarus, eastern Latvia and much of Estonia. In Scandinavia, its distribution is quite broad, though it is only found in southeastern part of Norway, as Ural owls may be found ranging across most of Sweden and Finland but is absent from the northern stretches as well as southern Sweden (largely the peninsular area). Its range in Russia is extensive but it is absent from areas where habitat is not favorable. In western and European Russia, it is found as far south roughly as the Bryansk, Moscow and northern Samara north continuously to Kaliningrad, the southern part of the Kola Peninsula and Arkhangelsk. In the eponymous Ural region, it is found from roughly Komi south to Kamensk-Uralsky. In the general area of Siberia, the Ural owl is found widely discontinuing its typical range in the foothills of the Altai Mountains to the west and being found north roughly as far as Batagay in the east. The species' distribution is continuous to the Russian Far East to as far as Okhotsk Coast and Magadan, Khabarovsk Krai and Sakhalin. Out of Russia, the range of the Ural owl continues into northeastern Mongolia, Northeastern China inland nearly as far as Beijing and down to Shandong and throughout the Korean Peninsula. The Ural owl is also distributed through all five of the main islands of Japan (i.e. only absent from Okinawa/Ryukyu Islands to the south). Vagrancy has been reported in Europe and Russia, which may account for sightings of the species almost throughout Germany. Furthermore, as many 16 records exist of the species turning until in northern Italy. Ural owls tend to occur in mature but not too dense primary forest, which can variously be in coniferous, mixed or deciduous areas. Normally, they prefer to be close to an opening. These are often compromised by forest bogs with wet ground underfoot is overgrown by a mixture of spruce, alder and/or birch or by damp heathland with scattered trees. Predominant trees in much of the range are often spruce, fir and pine forests in north and alder, beech and birch with mixtures of the above conifers in the south. Quite often they are adapted to high elevation forest in mountains, but in remote wildlands they can adapt equally well to areas down to sea level.<p>In the Carpathian mountains, they tend to favor almost exclusively beech-dominated forests, normally at elevations of 250 to 450 m (820 to 1,480 ft) above sea level. Forest characteristics of these beech-dominated woods showed that during forest management showed they need at least 100 ha (250 acres) of woods to persist, with parts of the forests needing to be at least 45–60 years old. Carpathian Ural owls typically occur far from human habitations and woodland edge not surrounded by forest and typically avoid parts of the forest with steep slopes or with dense undergrowth. Carpathian birds often preferred areas with glades that bear gaps between the trees often around 25 m (82 ft) or so and usually with plentiful broken trees. Young, post-dispersal owls in the Carpathians birds show less strong habitat preferences and may utilized wooded corridors that often are connected to remaining ideal habitat areas. Reportedly the countries of Slovakia, Slovenia then Romania have the most extensive ideal habitat in the Carpathians and resultingly have the highest local densities of Ural owls, perhaps in all of Europe. Forest predominant in beech were also seemingly preferred by the reintroduced Ural owls in Bavarian Forest, again with old growth preferred with plentiful sun exposure. Bavarian owls occurred in areas that were also often rich in large mammals since their preference for access to parts of the forest with broken trees and openings often coincided. Further north in Latvia, forests inhabited were usually far older than was prevalent in the regional environment, usually with a preference for forest areas with trees at least 80 years old. Finnish populations apparently most often occur in spruce dominated forest, usually having discreetly segregated forest preferences apart from sympatric species of owls except for the boreal owl, which also preferred spruce areas but occurred more regularly when the dominant Ural owls are scarce. In the taiga of western Finland, it was found that biodiversity was consistently higher in the vicinity of Ural owl nests than outside these vicinities, rendering the Ural owl as perhaps a “keystone species” for the local ecosystem. Riverine forests with birch and poplar are often utilized in the taiga as well as spruce or fir forests (montane taiga) in the Ussuri river area. Generally in northern climes such as Finland and western Russia, wherein the Lapland area the Ural owl is likely to reach the northernmost part of its range, it is adaptive to Subarctic areas possibly up to the tree line but does not adapt as well as the great grey owl to areas of dwarf forest just south of the tundra, generally needing taller, more mature forests to the south of this.<p>Historically, they normally occur in remote, little disturbed areas far from human habitations. The Ural owl is largely restricted from areas where forest fragmentation has occurred or park-like settings are predominant, as opposed to the smaller, more adaptive tawny owl which acclimates favorably to such areas. On the contrary, in some peri-urbanized areas of Russia, such as the metropolitan parks and gardens so long as habitat is favorable and encouraging of prey populations, the Ural owl has been known to successfully occur. Some towns and cities whose region hold some populations of Ural owls are Chkalov, Kirov, Barnaul, Krasnoyarsk and Irkutsk, and even sometimes Leningrad and Moscow. Changes in nesting habits due to the erection of nest boxes has almost allowed Ural owls to nest unusually close to human habitations in the western part of the range, especially in Finland. An exceptional record of synanthropization in this species for Europe was recorded in Košice, Slovakia where a 10-15 year apparent increase of an unknown number of owls have been observed between the months of November and June. At least one Ural owl was recorded to habituate the city of Ljubljana in Slovenia but there was no evidence it was able to breed or establish a territory given the limited nature of woodlands in the vicinity.

Migration

Resident species

Comportement

The Ural owl is often considered nocturnal with peaks of activity at dusk and just before dawn. However, taken as a whole and since it mainly lives the taiga zone where very long summer days are the norm against extensive dark during the winter, Ural owls are not infrequently fully active during daylight hours during the warmer months, while brooding young. Presumably during winter, they are mostly active during the night. Thus, the species may be more correctly classified as cathemeral as is much of their main prey. The wide range of activity times, and partial adaption to daytime activity, is further indicated by the relatively small eyes that the species possesses. This contrasts strongly with the tawny owl, which almost always fully nocturnal. During the day, Ural owls may take rests on a roost, which is most typically a branch close to trunk of a tree or in dense foliage. Normally, Ural owls are not too shy and may be approached quite closely. Historically, European birdwatchers often consider the species to be rather elusive and hard to observe. However, as the species as acclimated to nest boxes closer to areas where humans frequent, especially in Fennoscandia, encounters have increased sharply.<p>The Ural owl is a highly territorial and residential species that, as a rule, tends to stay on the same home range throughout the year. While most boreal owls, such as great grey owl and boreal owl, are generally given to nomadism and irruptive movements, with nearly the entire population following the population cycle of their primary prey, the Ural owl rarely departs from its home range even when prey populations decrease. Apart from the great grey species, like the Ural, most species in the Strix genus of owls are both highly territorial and non-migratory. Territories are generally maintained with songs, most often uttered by the male of the resident pair. This is quite the norm for owls in almost every part of the world. Due probably to its natural scarcity, very few firsthand accounts are known of territorial fights between adults but they presumably occur as Ural owls can be quite aggressive owls (or are at least in the context of protecting their nests). However, according to a study in southern Poland, Ural owls are generally less aggressive in the non-breeding seasons than are tawny owls to other owls and may be slightly tolerant of smaller owl species on their home range while the tawny is less so. That the Ural is slightly less aggressively territorial than the tawny owl is also supported in a study from Slovenia when tawnys had more spirited calls to recorded calls and launched more aggressive attacks to the taxidermied specimens of Ural, boreal and owls of their own species than did the Ural owls to any of the same stated stimuli. As for movements, as opposed to the sedentary adults, immatures may wander distances of up to about 150 km (93 mi). An occasional individual may wander straggle even further and remain for some time in a wintering area. A small number of straggling young Ural owls may occur irregularly down in southeastern Europe outside of the typical range of the species. Some circumstantial evidence was reported of Ural owls moving downhill in mountains in Japan when snowfall was heavy. Siberian population shows somewhat southward movements in severe winters, as the number of prey animals plummets and the owls themselves face risk of freezing.

Conservation

Tendance de la population

stable