Ural Owl

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Ural Owl
Ural Owl (Strix uralensis)

Ural Owl ( Strix uralensis )

Class : Birds (aves)
Order : Owls (Strigiformes)
Family : Real owls (Strigidae)
Genre : Strix
Type : Ural Owl
Scientific name
Strix uralensis
Pallas , 1771

The Ural or Uralkauz ( Strix uralensis ) is a large owl of the genus Strix within the family of authentics owl (Strigidae). It is similar to the tawny owl ( Strix aluco ), but is more contrasting in color, significantly larger and often more than twice as heavy as this owl . The closed range of the species lies in the boreal forest belt of the Palearctic and extends eastward to Korea and Japan . In addition, there are relic deposits in the Carpathian Mountains , the Beskids and the Dinaric Mountains . In the German-Austrian-Czech border area ( Bavarian Forest , Bohemian Forest and Šumava) and, most recently, in the Vienna Woods , some successful resettlement attempts are underway. Up to 15 subspecies are currently described; at least 8 are generally recognized, of which S. u. liturata , S. u. macroura and S. u. uralensis breed in Europe.

The coloring of the lower wings and the tail shows a certain similarity with the young goshawks ( Accipiter gentilis ), a fact that the German common name takes into account.


Ural Owl. Clearly the banded control springs and arm swing

The Ural Owl is a large owl with a large, round head, a distinctive face veil and a relatively long, rounded tail. As with all representatives of this genus , feather ears are not developed. The reddish to dark brown, slightly elongated oval and almond-shaped eyes are strikingly small. Some subspecies occur in a light or dark morph , with light individuals appearing more often than dark ones. In general, hawk-owls occurring further north are lighter than those living in more southern areas; in some the basic color of the body's plumage appears almost white. Overall, the individual variation in color is quite large, but the species can always be clearly identified if the observation conditions are sufficient.

Ural Owl (Strix uralensis)

The dorsal plumage of the Ural Owl is clearly brownish to black-brown on a whitish, ocher-colored or rust-brown background, dotted lengthways, sometimes also spotted. The upper tail-coverts are mostly gray-brown or beige, whitish marbled or lightly banded across. The rounded tail usually has five light, narrow transverse bands, the tip of the tail is light. In the light subspecies, the slightly darker shoulder and wing plumage is different from the lighter back plumage, in the darker subspecies there are hardly any color differences. This plumage area is clearly banded across, but usually does not show any white teardrop markings in the shoulder area, as is typical for the tawny owl. The basic color of the ventral side is lighter in all subspecies than the dorsal plumage, in S. u. liturata and S. u. uralensis almost white. It is irregularly dotted along its length, dark to black-brown, without transverse bands. The large, round head is hardly separated from the trunk. The face veil is light gray, brownish, in some subspecies also almost white. The dark radial lines are usually clearly pronounced. There is no zonal drawing, such as in the great gray owl ( Strix nebulosa ). The border is speckled with dark white and has a pearl-like effect. A blackish median line can be seen in most of the subspecies. The beak is yellow. The relatively long legs are bushy feathered including the toes; the claws are yellowish, the tips of the claws somewhat darker.

The sexes do not differ in terms of coloration, but females are slightly larger and, above all, much heavier on average. Males measure between 50 and 58 centimeters and reach a weight of almost one kilogram. The heaviest females of the subspecies S. u. macruora was found to weigh over 1.3 kilograms.

Even in their first age, it is difficult to distinguish young birds from adults. The best feature is still the presence of non-matured mesoptile feathers , especially on the under tail-coverts and on the leg fletching of the young birds. Young hawk owls look very similar to young tawny owls when they are in between.


Hawk owls have an extensive, individually often very differentiated sound repertoire. Established couples behave acoustically quite unobtrusively, so that the presence of such a couple can be overheard. Both partners have similar sounds and chants, whereby those of the male are usually duller, more modulated and overall more melodious, while those of the female have a sharper, rougher, often barking character. The Revierruf is a dull, melodious Hu ... huhuhu , whereby the first element is emphasized and the other syllables are often performed tremolously and at an accelerated pace after a pause . This far-reaching song can be heard over a kilometer. The male's nesting sound consists of hu- elements lined up next to one another , that of the female consists of barking sounds that sound like chro… chro… chro . In the event of disturbances, especially in the vicinity of the nest, continuous snapping can be heard.

During the autumn courtship, which is particularly noticeable acoustically when the territory is occupied, barking and yapping sounds are mainly uttered.


Distribution of the Ural Owl

The closed occurrences of the Ural Owl are in the boreal coniferous forest zone and the boreo-nemoral transition zone of the Palearctic. They begin in Europe in central Scandinavia and in the northeastern areas of the Baltic States and continue in a belt of varying widths across northern Russia to the Pacific coast. In East Asia, the species colonizes the entire Amur - Ussuri region, parts of the Chinese provinces bordering on it to the west, the mountain forests of North Korea to the south as far as the border regions with South Korea . Brood occurrences also exist on Sakhalin and the Japanese Islands . The southeastern deposits are on the uninhabited volcanic island of Torishima .

The Central and Southeast European holdings are considered to be Ice Age relic occurrences. They are located in the Beskids of the Polish-Slovakian-Ukrainian border region, in northeastern Hungary, in the Romanian Carpathians, in Slovenia and in the forested areas of the Dinarides of Croatia , Serbia , Bosnia , possibly also Montenegro and Macedonia . A very small, isolated residual population exists in Bulgaria .

Historical occurrences in Austria and Germany

In Austria the Ural Owl bred sporadically in the 19th century, but regularly in Carinthia and occasionally in Styria . Breeding pairs were found there until 1950. Broods from the Almtal are known from Upper Austria . Despite the sporadic broods, the species is considered extinct in Austria.

In Germany, the Ural Owl was a breeding bird in the Bavarian Forest until the mid-1920s. In the 19th century, individual birds were hunted here again and again, and there were also finds of clutches and dune cubs as evidence of breeding. The last shooting took place in 1923 on Kaitersberg . At around the same time, the deposits on the Czech side of this forest area became extinct. The last evidence there comes from Sušice around 1926. Direct tracking by shooting was probably the main reason for the disappearance of this species from these regions.

In southern Carinthia there are probably occasional broods of elapsed hawk owls from Slovenia and in the Italian-Slovenian border area this species has been breeding regularly at least since 1994.

Resettlement Projects

In the Bavarian Forest National Park , in the Bohemian Forest and in the Šumava nature reserve, attempts to reintroduce citizenship are underway, which on the German and Czech sides have probably led to a self-sustaining population of around 10 breeding pairs each.

In the Bavarian Forest National Park, for example, the national park administration has repeatedly released rebred owls since 1975. In 1989 the first successful free-range brood took place. In 2012, ten occupied areas were estimated in the national park area.

On the Austrian side, the action was suspended for the time being due to the illegal shooting of owls and persistent protests by the hunters who feared a negative impact on small game hunting. A specific animal welfare project of the Association for Landscape Management & Species Protection in Bavaria eV , established in 2015, was the reintroduction of the Ural Owl in the Steinwald Nature Park in the Upper Palatinate.

A new resettlement campaign initiated and managed by the Research Institute for Wildlife Science and Ecology at the University of Veterinary Medicine, Vienna , with release sites in the Dürrenstein-Lassingtal wilderness area and in the Vienna Woods is in the project phase and is showing initial successes. In 2011, for the first time in more than half a century, a pair of Ural Owls brooded again in the Vienna Woods. In 2012, a year with very strong mouse degradation in the area, at least 11 broods were found in the Vienna Woods and in the area of Amstetten and Scheibbs , 9 of which were successful and brought the unusually high number of thirty young owls to fly. The evaluation of the data from telemetered birds and the reading of the colored rings have confirmed that there is an exchange of breeding birds between the individual breeding areas. The breeding pair in the Amstetten district consisted of a male from the Dürrenstein release area and a female from the Vienna Woods. After the breakdown of the mouse gradation, there were no broods in the release area in 2013. In 2014 the food situation in the Vienna Woods improved significantly, so that again 17 young owls came to fly. In the Dürrenstein area only one brood with two fledged owls was successful when the food supply was significantly poor. In 2015 there was only one pair in the Vienna Woods, but four pairs in the Dürrenstein wilderness area. Two broods took place on natural nesting sites in red beeches. A very good supply of food and a large number of new nesting boxes meant that 50 young owls came to fly in the two release areas in 2017. As has been observed for a long time, the gender ratio of 3: 2 in favor of the males is strikingly unequal.

In 2014, 26 breeding grounds were occupied in the Bavarian Forest and in Friuli, in the area of ​​the upper reaches of the Natisone , two nest box broods with a total of three young owls were found.


Hawk owls are generally extremely faithful to their location. Of several thousand birds ringed when they were nestling in Finland , 86% resettled within a radius of less than 50 km from their place of birth. Territory owners move only a few kilometers from the breeding site if there is sufficient food. Nonetheless, further migrations seem to occur and to be frequent, especially with North Siberian birds. In Europe, too, isolated specimens pass over long distances and can appear far from the next breeding grounds. A Ural Owl found dead in Saxony-Anhalt in 1987 had been ringed in Estonia the year before ; So in his first winter he had walked over 1,000 kilometers.


Ural owl in natural habitat in Finland
Habitat of the Ural Owl in the Dinaric Mountains

The Ural Owl is not tied to specific forest types. In its main area of ​​distribution in Scandinavia and the Russian taiga belt, it inhabits spruce-dominated forests interspersed with birch and alder with a rather open tree population. Ural owl habitats are often found on the edge of clearings, in clear-cut or bog areas. Standing or slow flowing waters are also part of the preferred inventory. In addition to the availability of open areas with a good range of small mammals, sufficient nesting opportunities are essential, be it in the form of natural caves, nesting boxes or old bird-of-prey nests. The species does not inhabit dense, contiguous forests, and steep slopes are avoided. In the southern breeding areas of East Asia the Ural Owl penetrates into the zone of the evergreen deciduous forests.

The remaining populations of Central and Southern Europe prefer open mixed beech forests with little undergrowth; Sunlit, light slopes that have border structures with meadows, pastures and clearings as well as bodies of water are ideal. Where the owl coexists with the tawny owl, the latter populates the denser forest areas, while the Ural owl prefers lighter forests and open, varied structures. Where hawk-owls are not pursued, they do not avoid proximity to human settlements; in Central and Southern Europe, however, the species is extremely hemerophobic , that is, shy of people. In these central and southern European distribution areas, the Ural Owl is considered to be an inhabitant of the low mountain range. In fact, there does not seem to be a clear preference for settlement at a certain altitude level as long as suitable habitat structures are available. The preference for low mountain ranges in Central Europe is likely to be the result of habitat destruction in lower altitudes.

In general, the owl owl takes up quite a lot of space, depending on the size of the species, about three times larger than that of the tawny owl. In the average Ural Owl habitats in Scandinavia, around 5–7 pairs breed per 100 km², with a nesting distance of between two and four kilometers. In optimal areas, however, significantly higher settlement densities were found with very good food availability: for example, in 1992 near Kraków, 3 pairs brooded in a forest area of ​​only 10 km². Even higher settlement densities with up to 10 districts on 10 km² are suspected according to recent studies in southern Slovenia.

Food and loot


The Ural Owl is both a raised hide and a search flight fighter. He can beat prey up to the size of a small hare or a capercaillie . Mice and shrews, however, form the basic foodstuffs at all times of the year, with voles playing a particularly dominant role; in gradation years their share can exceed 90 percent. Among the species from this family, earth voles , bank voles and water voles predominate as prey . In winter, shrews and birds become more important prey animals. Among the bird prey, which is usually less than 10 percent, are mainly thrushes and pigeons , but also larger species such as crows and hens , and occasionally tawny owls. In Central Europe, the dormouse should also represent a not unimportant dietary supplement. It is not uncommon in beech forests and with a mass of up to 240 grams it is a productive prey. Investigations from Slovenia showed a large proportion of these dormice in the total hive, especially after the breeding season . Remnants of amphibians , reptiles and fish are regularly found in the ridges , but only play a subordinate role in terms of quantity and weight, while larger insects, especially beetles , can play a significant role in other food shortages. Hawk owls occasionally ingest carrion .

The daily requirement of food varies from year to year between 147 and 255 grams, for a non-breeding couple an annual requirement of 109 kilograms of live weight of prey was calculated.

Loot acquisition

The preferred hunting method is high-seat hunting from waiting areas, which are often at a high altitude. The owl sits relatively upright, the head is angled downwards by about 90 °, the face veil is spread. If a prey is spotted or acoustically located, the owl leans forward almost horizontally and lets itself fall in an inclined steep flight. Smaller prey animals are often killed by the violent impact, larger ones by multiple neck or head bites. In search flight hunting, which is rarely used, the owl patrols in a slow, ground-level flight over its hunting ground and often drops in an abrupt turn when locating a prey. Occasionally, short periods of shaking have been observed during this hunt . Larger insects are caught in flight with their fangs; the methods of bird hunting are not known.

The owl transports small prey in its mouth or in its beak to a feeding place, less often it consumes them on the spot. Larger prey are cut up into bite-sized pieces; in birds it usually only eats the breast meat, in mammals the entrails are not used. Hawk owls create food depots all year round in caves, crevices, but also in decayed tree stumps.


The vaults of the Ural Owl are up to 94 mm long and up to 35 mm thick, the average is 62 × 25 mm. They are very firm and slightly pointed at the ends. Since hawk owls often change daily dives outside of the breeding season, they are difficult to find.


Activity, rest and comfort behavior

Hawk owls are crepuscular and nocturnal. During the breeding season, however, they hunt until late in the morning, sometimes during the day. The first peak of activity is at dusk and extends to around midnight. This is the time of the greatest call intensity. After a rest and cleaning break, there is a second activity highlight that lasts until the early hours of the morning. In the short Nordic summer, the main activity does not begin until around midnight and is only interrupted by small cleaning breaks.

The owl often changes the daily dives. They are often very low on storage wood, tree ruins or in afforestation. During the breeding season, however, they are always close to and within sight of the nesting site. When the owl rests in a taller tree, it often chooses weak side branches and presses close to the trunk. Outside of the breeding season, the partners' daily doses are far apart; mated hawk owls can only be found dozing close together, sometimes in mutual physical contact, during the mating period.

Hawk owls spend a lot of time grooming their plumage. They sunbathe extensively, especially on winter days, and specifically seek out places that are exposed to the sun. They often bathe, especially during breeding and moulting, and mostly go underground. In light rain they can be sprinkled with spread plumage, while in persistent heavy rain they seek sheltered resting places or take a protective position.

Territorial and enemy behavior

Ural owls are territorial all year round and extremely aggressive, especially during the breeding season. They defend their territory from conspecifics, but also from smaller species, especially the tawny owl. Opponents are approached directly and attacked with the claws. The attack flights on humans, but also on red deer or wild boar , if they get too close to the nesting area are characteristic of the species . These attacks usually take place surprisingly from behind, after the bird has often followed the intruder unnoticed for a long time. During these attack flights, the owl grazes its prey in the head, shoulder or back area and occasionally injures it considerably. It has also been observed that the owl claws into a part of the body and can be dragged along with it. Females are more active and aggressive than males in these attacks. The Swedish name Slaguggla ('attacking owl') is due to this behavior.

On the other hand, hawk-owls can behave little shy, almost trusting and curious outside the breeding season, which has greatly facilitated their persecution by humans. They can show behavior that is interpreted as conflict sleep, in which they allow approaches up to a few meters motionless before they are blown.


Nest box for Ural Owl in Finland

Hawk owls lead a largely monogamous permanent marriage, which, however, outside the breeding season is characterized by distance and pronounced intraspecific aggressiveness. Biandrie has only been observed in captive broods. The females become sexually mature at the end of the first year of life, probably also the males. However, annual females only brood in exceptionally good mouse years, and two-year-old females usually do not breed yet.

Courtship, pair formation and nesting place

Unfertilized egg from a Finnish clutch

The mating begins during the autumn courtship and is characterized by loud series of calls, but also by the great aggressiveness of the two partners. This is the time when the district chants can be heard most frequently and completely. The main courtship begins in January. Acoustically, this phase is characterized by the male's nesting call series and various contact calls. The first handover of prey also takes place, so that the mutual need for distance is gradually reduced until it is largely eliminated during joint nesting site inspections, and possibly even when they slip into a cave together. During this time, the partners can rest close together, sometimes in mutual physical contact; Also, crawls and mutual plumage care were observed. When the prey handover becomes more frequent and males and females prepare the nesting site for egg-laying with rotating movements in the nest hollow, the first copulations also occur, usually on a branch near the nesting site.

Preferred nesting places are large Ausfaulungen in old trees, stumps, which have trough-shaped recesses on its upper side, as well as old birds of prey, Corvids - or Schwarzstorch clumps . Occasionally owl broods can also be found on rock ledges; ground broods also occur. Nest boxes are gladly accepted. The nesting site is prepared by turning and trough movements, protruding chips are nibbled off in caves. The owl, like all other owls, does not enter nesting material.

Clutch and brood

Ural owl in the early migration stage. About 30 days old
Branch in the forest of Albu , Estonia

In good vole years and with little snow, the laying period of Central European Ural Owl populations begins in mid-February, but usually in mid-March. Northern Scandinavian and Siberian birds begin to lay eggs in April. Fresh clutches can still be found in June. If the food situation is poor, the broods can often fail for several years. Hawk owls only breed once a year, nothing is known about replacement clutches in the event of clutch loss. During the breeding season, the male provides food for the female.

At an interval of 2–3 days, the female usually lays 3–4 (1–6) initially pure white, round oval eggs which, with an average of 50 × 42 mm and a weight of 50 grams, are the size of a small hen's egg. The female breeds very firmly from the first egg. The first chick hatches after about 28 days, the others follow according to the laying intervals. You and the female are provided with food by the male alone for the first few weeks; the female tucks the chicks and divides the food. The chicks develop very quickly. After about 5 weeks, the youngsters, who are only capable of fluttering, jump out of the nesting place and then try to work their way up a tree as quickly as possible with the help of the claws and beak and to get to a safe height and a protected position. This high-risk phase of life, which often lasts several days, is known as the wandering stage . The branchlings will be looked after by both parents for another 60 days. They can fly relatively safely at 90 days of life and leave the breeding area a little later.

Breeding success and life expectancy

The annual reproduction rate of the Ural owl fluctuates very strongly during the breeding period, especially depending on the availability of food and the climatic conditions, and is between 0.9 and 2.9 fled-out young per brood that has started. A Swedish study identified 1.8 young owls in a seven-year census.

Of these, around 60 percent survive the first year of life, of the remaining 70 percent the second, after which the death rate flattens a little. After two years, significantly less than half of the owls of one cohort are still alive.

The maximum age of a ringed Ural Owl found in the wild is 22 years; an aviary bird was 30 years old.


The Ural Owl is a species within the genus Strix , in which between 18 and 24 species of forest-dwelling, medium-sized to large owls are grouped together. Up to 20 subspecies have been described. König & Weick consider the rating of 8 to be justified. There are two different groups of races: the relatively large, except for S. u. macroura rather light, Palearctic mainland forms as well as the smaller, brownish, Japanese island forms. The Sichuan owl ( Strix davidi ), often referred to as a subspecies of the Ural Owl, is now considered a separate species.

  • Strix uralensis uralensis Pallas , 1771 : The nominate form inhabits by far the largest distribution area, which extends in the east from the Pacific coast to the upper reaches of the Volga in the west. The subspecies appears in a light and a (rarer) dark morph.
  • Strix uralensis liturata Lindroth , 1788 : This subspecies inhabits northern Europe eastwards to the Volga, where it is associated with S. u. uralensis mixed. It is slightly larger, heavier and slightly darker than the nominate form.
  • Strix uralensis macroura Wolf , 1810 : The largest subspecies inhabits the relict habitats of Central and Southeastern Europe. It also occurs in a melanistic, coffee-brown morph with little contrast. Especially in the Dinarides, this color variant seems to be not uncommon with up to 10%.
  • Strix uralensis yenisseensis Buturlin , 1915 : This subspecies is somewhat smaller, darker and shorter-winged than the nominate form with which it mixes in large areas. Their distribution area is in northern Siberia, in winter individuals of this type appear in northeastern Mongolia and the Baikal area.
  • Strix uralensis nikolskii Buturlin , 1907 : This subspecies resembles S. u. liturata , but the head and shoulder region has a brownish hue. Their distribution area extends from the Baikal region southeast to Korea.
  • Strix uralensis fuscescens Temminck & Schlegel , 1850 : A relatively small subspecies that is common in West honshū and parts of Kyushu . Overall impression reddish brown with yellowish markings; the ventral side is dashed dark brown on a cream-colored background, in which distinctive white drop marks are often embedded.
  • Strix uralensis hondoensis ( Clark AH , 1907) : This subspecies is also smaller than the mainland races and is rust-brown overall. The white components in the head and neck area are largely missing. S. u. hondoensis is a breeding bird of the northern and central Honshu.
  • Strix uralensis japonica ( Clark AH , 1907) : This subspecies distributed on Hokkaidō is somewhat smaller than S. u. nikolskii , to whom she largely resembles.

Inventory and inventory development

The owl owl population is considered to be harmless, but no population figures are available over large areas of occurrence. In Europe, populations are increasing in most regions, largely due to the installation of nest boxes and the decrease in direct tracking. Another reason for the population increase, especially in Russia, is the local method of clear-cutting management, which opens up new hunting areas in the succession areas of the species.

About 1,000 pairs breed in Central Europe, the total European population is estimated at 82,000 breeding pairs, of which 65,000 breed in the European part of Russia alone. In addition to direct tracking, road traffic and obstacles, such as pasture fences, are a major source of danger, as uddy owls often fly close to the ground and also cross open spaces in a flight close to the ground. Changed management methods, which rigorously rejuvenate the forests, so that both cave trees and old bird-of-prey nests are missing, have a regionally reduced population.

The Ural Owl is considered to be one of the species that will be affected by climate change. A research team that, on behalf of the British Environmental Protection Agency and the Royal Society for the Protection of Birds, examined the future development of the distribution of European breeding birds on the basis of climate models, assumes that by the end of the 21st century the owl owl's range will mainly be in South will shrink considerably. Among other things, the breeding area in the Carpathian arch that still exists today is affected . Overall, the distribution area is shifting further north, whereby it is forecast that new, suitable breeding areas will be found in the north of Fennos Scandinavia and Russia.


Web links

Commons : Ural Owl  - Album with pictures, videos and audio files

Individual evidence

  1. a b HBV (1994) vol. 9. p. 613
  2. Mebs & Scherzinger (2000) p. 205
  3. area of a male vocal (MP3, 1.6 MB) on xeno-canto.org
  4. a b c d HBV (1994) vol. 9. p. 611
  5. Mebs & Scherzinger (2000) p. 206
  6. Workshop p. 72
  7. Wolfgang Scherzinger: The bird world of the primeval forest areas in the interior of the Bavarian Forest . In: Bavarian Forest National Park , issue 12, 1985, p. 123
  8. Zink & Probst (2009) p. 611
  9. Thomas Rödl, Bernd-Ulrich Rudolph, Ingrid Geiersberger, Kilian Weixler, Armin Görgen: Atlas of the breeding birds in Bavaria. Distribution 2005 to 2009 . Verlag Eugen Ulmer, Stuttgart 2012, p. 125
  10. https://www.landschaft-artenschutz.de/habichtskauz-projekt/
  11. ^ Resettlement Austria project website
  12. Mail from the University of Veterinary Medicine, Vienna
  13. ↑ The rarest owl in Central Europe regains a foothold in Austria , derstandard.at, May 12, 2012
  14. Richard Zink, personal communication, Eulenpost June 2014
  15. Richard Zink, personal communication, Eulenpost December 2015
  16. personal communication from the project leader, Richard Zink; Owl Mail July 2017
  17. Richard Zink, personal communication, Eulenpost June 2014
  18. Richard Zink, personal communication, Eulenpost December 2015
  19. a b c d e f g Mebs & Scherzinger (2000) p. 223
  20. a b Zink & Probst (2009) p. 21
  21. König & Weick (2008) p. 382
  22. Mebs & Scherzinger (2000) p. 208
  23. Workshop (2007) p. 20
  24. Mebs & Scherzinger (2000) p. 215
  25. HBV (1994) Vol. 9. P. 627f
  26. Zink & Probst (2009) p. 20
  27. Workshop (2007) p. 17
  28. HBV (1994) Vol. 9 p. 628
  29. Brown & Ferguson & Lawrence & Lees (2003) p. 131
  30. a b Mebs & Scherzinger (2000) p. 213
  31. Mebs & Scherzinger (2000) p. 216
  32. HBV (1994) Vol. 9 p. 627
  33. König & Weick (2008) p. 354
  34. König & Weick (2008) p. 381
  35. Workshop (2007) p. 19
  36. Data sheet Birdlife international (2009)
  37. Workshop p. 6
  38. ^ Brian Huntley, Rhys E. Green, Yvonne C. Collingham, Stephen G. Willis: A Climatic Atlas of European Breeding Birds , Durham University, The RSPB and Lynx Editions, Barcelona 2007, ISBN 978-84-96553-14-9 , P. 257
This version was added to the list of articles worth reading on August 9, 2009 .