Gyrfalcon
| Gyrfalcon | ||||||||||||
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Gyrfalcon ( Falco rusticolus ), white morph |
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| Scientific name | ||||||||||||
| Falco rusticolus | ||||||||||||
| Linnaeus , 1758 |
The gyrfalcon ( Falco rusticolus ) is the world's largest species of falcon. It is circumpolar in the arctic regions of Eurasia and North America as well as Greenland and colonizes the tundra there . In Central Europe it can only be seen very rarely as a winter visitor and then mostly stays near the coast.
The gyrfalcon, whose horizontal flight speed exceeds that of the peregrine falcon , has been valued as a bird of prey (hunting falcon) since the Middle Ages . White gyrfalcons were considered to be particularly valuable and were regularly among the gifts to and between royal houses.
Appearance
Body size and identifying features
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The gyrfalcon, about the size of a buzzard, is the world's largest species of falcon. The body length of a gyrfalcon is between 48 and 61 centimeters. 19 to 24 centimeters of the body length are accounted for by the impact ( control spring ). The wingspan is between 105 and 131 cm. The species shows a clear sexual dimorphism in terms of size and weight ; Males weigh 960 to 1300 grams, on average 1070 grams, females 1400 to 2000 grams, on average 1710 grams. The differences in color between the sexes, on the other hand, are small; males tend to have a slightly paler plumage than females.
The wings are wider, especially at the base of the body, the arm wings are longer and the hand wings are fuller and more pointed than those of the peregrine falcon. The long and broad tail is striking. The wax skin and feet of young birds are blue-gray. Adult birds, on the other hand, are yellow in color. The iris is dark brown, the ring around it is yellow. The beak is gray-blue in color; the tip of the beak is clearly darker.
The different color morphs
The plumage color of the gyrfalcon is very variable. There are white color morphs that only have black wing tips and those whose plumage shows a multitude of dark spots. There are also color morphs with a monochrome gray or gray-brown body upper side, gray birds with dark horizontal stripes and a light underside as well as almost monochrome black-brown individuals.
In the ornithological literature, gyrfalcons are usually referred to as trimorphic, and white, gray and dark gyrfalcons are distinguished. The different color morphs are repeatedly described as geographic. The white color morphs, which used to be popular in falconry, are mainly found in Greenland and Eastern Siberia; gray gyrfalcons, on the other hand, are typical of Iceland and southern Greenland, while the dark color morphs occur mainly in Scandinavia, northern Finland and northern Russia. The ornithologist Todd pointed out as early as 1963 that the color of the plumage of the gyrfalcon is more of an individual than a geographical characteristic. The detailed statistical analyzes carried out by the ornithologists Potapov and Sale on the basis of 1310 bird hides confirm this. Different color morphs can occur in all populations: Of 55 adult gyrfalcons that were observed on the Seward Peninsula in Alaska in 1968 , 12.7 percent were brown-gray, 56.4 percent gray, 16.4 percent light gray, 5.5 percent pointed cream-colored plumage with gray horizontal stripes and 9.1 percent were white. The proportion of a specific color morph in the population is evidently subject to fluctuations. The proportion of white gyrfalcons on the Kamchatka Peninsula was 39.3 percent between 1981 and 1990 and fell to 20 percent for the period from 1991 to 1999.
Subspecies
According to the current state of knowledge, the gyrfalcon is a monotypical species. In the older ornithological literature one can still find between four and seven subspecies, depending on the author. The differentiation into subspecies was based on the different plumage colors that can be observed in gyrfalcons. Carl von Linné even assigned the color morphs to different types. Since the definition of a subspecies presupposes a distinct distribution area, but the color morphs can occur in all populations, from today's perspective the plumage color is no longer a basis for the delimitation of subspecies.
The large falcon population, which used to be sometimes referred to as Altai falcon or Altai gyrfalcon ( Falco altaicus ) and is found in the Central Asian Altai and Sajan Mountains , is now considered a subspecies of the saker falcon ( Falco cherrug milvipes ), whereby a genetic differentiation of this subspecies from the gyrfalcon is not possible. It is possible that this subspecies had multiple contact with the gyrfalcon after its spread in Central Asia, so that hybridizations occurred.
Possible confusion
In field observations where the size of a bird is difficult to determine, it is easy to confuse gyrfalcons with other hawk-like or raptor species . The silhouettes of the somewhat smaller saker falcon and the gyrfalcon are similar. The saker falcon has a more contrasting colored head than the gyrfalcon with the white over-eye stripe and the dark beard stripe. The usually much smaller peregrine falcon also shows a clear contrast between the beard and the light cheeks on the head, which is usually missing in gyrfalcons. When observing the field in Northern Europe, the goshawk is particularly difficult to distinguish from the gyrfalcon at a great distance . The hawk, however, has a slightly S-shaped curved trailing edge of the wing, the tail is more fan-shaped. In hawks gliding phases alternate with a few flight strokes. With the gyrfalcon, on the other hand, the active flight phases are significantly longer.
Distribution area and habitat
Habitat and worldwide distribution area
The gyrfalcon is a circumpolar falcon species whose breeding areas are in the Arctic and Subarctic . The southern breeding records are for Eurasien on the Kamchatka -Halbinsel at 54 ° 35 'N, 161 ° 7' O and North America Long Iceland on the southeast coast of Hudson Bay at 54 ° 53 ' N , 80 ° 30' W . In Europe, it is a breeding bird in Iceland, Norway, Sweden, Finland and Russia. In Asia it only breeds in Russia. The American breeding areas are in the US state of Alaska as well as Canada and Greenland.
The northern limit of its breeding area is essentially determined by the occurrence of its most important prey, the Alpine grouse and the willow grouse . Although the gyrfalcon is described in the literature as the hawk species of the High Arctic , peregrine falcons, which have a broader range of prey, occasionally breed further north than this species. For the hunting behavior of the gyrfalcon an open landscape with only low bushes is necessary. The breeding grounds must also have rocky cliffs or forest islands. Characteristic breeding grounds are therefore tundras, cut through by rocky river valleys, and rocky coasts near seabird colonies. The southern limit of its distribution is represented by the regions in which the forest tundra or forest steppe changes into denser forest stands.
The Eurasian breeding areas
Gyrfalcons breed in all areas of Iceland , with the greatest population density in the north of the island. The southernmost breeding areas in Norway are in Sirdalsheiene and extend from there to the valley of the Pasvik River in northern Norway. In Sweden, the gyrfalcon is almost exclusively a breeding bird on the alpine tundra. It breeds in the northern part of Dalarna , in the west of Jämtland as well as in Härjedalen , Lapland and in the north of Norrbotten . The breeding area in Finland is limited to northern Finland. The area of the two northern Finnish municipalities Inari and Utsjoki is said to have the highest population density of gyrfalcons in Finland. No complete information is available about the breeding areas in Russia, so that the northern and southern distribution limits in this region have so far only been insufficiently determined. Potapov and Sale point out that many Russian ornithologists deliberately refrain from publishing evidence of breeding in order to prevent the nests from being robbed. According to the current state of knowledge, the breeding areas of the gyrfalcon extend from Finland over the Kola Peninsula to Siberia and are mainly north of the Arctic Circle . However, gyrfalcons are absent from Russia's arctic islands.
The breeding areas in Alaska, Canada and Greenland
The breeding area in North America extends in Alaska from the Aleutian Islands over the Seward Peninsula and the Brooks Range to the Chugach Mountains . In Canada, gyrfalcons breed on most of the Arctic islands , including Ellesmere Island , as well as in the arctic lowlands and forest steppes. Evidence of breeding has so far been found for the Canadian provinces of British Columbia , the northern part of Québec and Labrador . In Greenland, gyrfalcons breed only in the coastal region.
train
The different populations of the gyrfalcon show no uniform migration behavior. The gyrfalcons living in the Western Palearctic are standing and mooring birds . With the gyrfalcons living in the Scandinavian region, adult birds mostly stay in their territory all year round. Only young birds roam more so that individual specimens can also be observed in Denmark, Ireland and Great Britain during the winter half-year.
The gyrfalcons living in the Russian tundra zone, on the other hand, are migratory birds that migrate from the tundra to the taiga zone, covering a distance of 1,000 to 2,000 kilometers. The gyrfalcons that breed in eastern Greenland migrate to Iceland in September and return to their breeding grounds in April, while the rest of the birds overwinter in the southern coastal regions of Greenland.
Reproduction
Courtship and mating
The trigger for courtship behavior is usually a sufficient presence of ptarmigan , since the gyrfalcon almost exclusively hits these prey, especially in the early reproductive phase. Exceptions to this rule are regions in which there is an abundance of other prey such as lemmings or sea birds . The courtship often begins in February. The courtship behavior is no different from that of other falcons. Courtship behavior includes pawing the nest, the handing over of food from the male to the female, intense calling and bowing of the birds to each other, with the beak not pointing at the partner and the plumage being tight. The male gyrfalcon uses courtship flights to indicate the eyrie to the female. These include circular flights high above the eyrie as well as eight-shaped flight figures directly in front of the nest. The cross point of this figure eight-shaped flight figure is directly in front of the nest. Often it even carries a prey in its beak.
The pairings usually do not take place near the eyrie and continue until the beginning of the egg-laying process.
Breeding area and nest
The size of a gyrfalcon breeding area is between 63 and 137 square kilometers. Only the immediate vicinity of the nest is defended, with conspecifics more likely to trigger aggression than other birds. Nests of other falcon-like species such as the peregrine falcon have been found less than 250 meters from the gyrfalcon's eyrie. On the other hand, the hunting grounds of neighboring gyrfalcon pairs can overlap. The smallest distance that has been measured so far in Iceland between the nests of neighboring gyrfalcon pairs was 5.5 kilometers.
As is typical for falcons, gyrfalcons do not build their own eyrie. They either use protected areas below rocky outcrops in steep rock faces and lay their eggs there directly in a hollow in the ground padded with moss and lichen, or they use clumps of other birds such as the common raven , golden eagle , sea eagle or buzzard . Common ravens' nests in particular are often used by gyrfalcons. Gyrfalcon pairs are usually able to chase away ravens from their newly built nest and to occupy it. Something similar has also been described for golden eagles, whose nests are used by gyrfalcons, especially in Alaska. In one case, a pair of golden eagles gave up their eyrie after the first egg-laying, after an unmated gyrfalcon repeatedly attacked the eyrie. Birds that breed in the forest tundra also use existing tree nests. Gyrfalcons are very loyal to their territory and use clumps again and again. A use over decades has been proven for individual clumps.
Egg laying
In Iceland, Canada, Russia and Scandinavia, females were observed laying eggs at the beginning of April. In the high Arctic, however, the female does not begin to lay her eggs until May. The gyrfalcon is therefore probably the bird of the Arctic with the earliest start of breeding. Only for the common raven it cannot be ruled out that it will start breeding even earlier.
The female begins to live exclusively on prey brought by the male about 10 days before the start of oviposition. The prey is usually passed in the air between the two parent birds.
The laying interval between the individual eggs is two to three days. The eggs are yellowish in color and mottled or speckled reddish brown. A clutch of falcons usually has between three and four eggs. The female occasionally sits on the nest after the first egg-laying. The actual brood usually begins after the third egg is deposited. The breeding season is about 34 to 36 days. The male is mostly busy getting food. According to field observations in Canada, the proportion of the male in the incubation of the eggs and the later huddling of the nestlings is estimated at 17 to 24 percent.
Fledglings
The hatching of the young birds is almost synchronous. Most of the young birds in a clutch have hatched within 72 hours. The chicks show no aggressive behavior towards one another. During the breeding season and the first 18 to 25 nestling days, only the male brings the food. The feed transfer between the female and the male usually takes place outside the nest in the first days of the nestling. The female flies towards the male and takes over the prey in the air. Occasionally, however, the male lays the prey on a ledge not far from the eyrie and the female fetches it from there. As a rule, females do not begin to take part in procuring food for the young birds until the end of the third week of nestling. From then on, the male also carries food directly into the nest. Males usually hand over all of their prey to the young. Females often feed the young birds throughout the nestling period.
The young leave the nest between 46 and 53 days old. On average, 2.3 cubs fly out per year and couple. They will be provided with food by the parent birds for another four to six weeks. Sometimes the gyrfalcons stay on the ground for up to a week after their first flight and are fed there by their parent birds. The first prey they catch themselves are usually the young birds of other bird species as well as smaller mammals. In the regions where ptarmigan are the main prey, the fledgling of the young ptarmigan coincides with the first attempts at hunting by the gyrfalcon.
With the beginning of the breeding season, the female also begins moulting . This continues until October and November. In the male, which the female supplies with prey during the breeding season and later also the young birds, moulting usually begins two weeks later.
Life expectancy
The survival rate of young gyrfalcons has not yet been adequately investigated. It is believed that 50 percent of fledged gyrfalcons die in the first year of life. The death rate drops significantly after the first year of life - research in Iceland suggests that nine out of 10 adult gyrfalcons will reach the next year of life. Infestation by ticks and nematodes can contribute to the weakening of adult birds .
Female gyrfalcons reach sexual maturity in their second or third year of life. Male gyrfalcons do not reproduce for the first time until they are four years old. The oldest ringed gyrfalcon to be found so far was a male who lived to be twelve years old.
Food and subsistence
The main prey of the gyrfalcon is usually ptarmigan. During egg-laying in particular, ptarmigan make up up to 98% of the prey spectrum. The range of prey also includes lemmings, mountain hares , various small bird species as well as grouse and ducks. Their share of the total loot spectrum increases with the onset of the Arctic summer. Gyr falcons that breed near seabird colonies also beat seagulls and limicoles .
Two hunting techniques are typical of the agile and fast gyrfalcon. Either it comes down steeply on the prey from a circling search flight. According to individual observations, he can dive at a speed of 160 to 208 kilometers per hour. Alternatively, the gyrfalcon flies close to the ground and surprises seated or soaring birds. This fighter flight is occasionally interrupted by sitting in low waiting areas.
Both hunting techniques result from the fact that the hunting success of a gyrfalcon is greatest when it hits ptarmigan in the first few seconds after they have blown up. The ptarmigan have not yet reached their full flight speed and can only avoid the gyrfalcon's flight maneuvers to a limited extent. In level flight, ptarmigan can fly faster than gyrfalcon for short distances and regularly manage to escape it. We know from falconry that gyrfalcons occasionally chase their prey up from their cover and pursue them in flight until they are exhausted and forced to land. The prey is then hit on the ground.
The food requirements of gyrfalcons are estimated to be about 240 grams of meat per day for a male and about 300 grams for a female gyrfalcon. The nutritional requirements of nestlings changes during the nestling period, but averages around 170 grams. In order to cover the food requirements of two adult gyrfalcons and three nestlings, the parents have to beat around three Ptarmigan a day.
The prey is killed, if not already by the force of the impact, by a subsequent bite in the neck or the back of the skull. Usually the prey is plucked and eaten on the spot. Prey is transported to the eyrie with the catches if there are nestlings to be looked after. If the hunt is successful, food depots are also created. Gyr falcons hunt both during the day and at dusk. They can still see very well even in low light.
Duration
It is very difficult to observe gyrfalcons in the wild, so population figures are usually based on rough estimates. In the 1970s, the Norwegian population was estimated at only 10 to 12 breeding pairs. In the 1990s that number was then corrected to between 300 and 500 pairs. The ornithologists Potapov and Sale therefore chose a statistical approach in which they first determined the total area of habitats suitable for gyrfalcons. According to their calculations, there are around 1.5 breeding pairs per 1,000 square kilometers of suitable habitat. They therefore estimate the worldwide population to be just over 11,000 breeding pairs. The most recent population estimates of the countries in which Gyrfalcons breed, which Potapov and Sale have compiled, result in a minimum population of 7,880 breeding pairs and a maximum of 10,990. Canada has the largest population with 2,550 to 3,200 and Russia with 3,500 to 5,000 breeding pairs. In the Western Palearctic, an average of 1,028 pairs of gyrfalcons are believed to breed.
The gyrfalcon is one of the species that are particularly affected by global warming. A research team that, on behalf of the British Environmental Protection Agency and the RSPB, examined the future distribution of European breeding birds on the basis of climate models, assumes that the breeding area of the gyrfalcon will decrease by more than 60 percent by the end of the 21st century. According to this forecast, the breeding area in Iceland, Fennos Scandinavia and northern Russia in particular will decrease significantly. Potential new breeding areas are emerging on Svalbard and in the south of Novaya Zemlya , but these cannot compensate for the loss of the other breeding areas.
Systematics
The systematic classification of the gyrfalcon is controversial today. According to recent genetic studies, the gyrfalcon forms a monophyletic group together with the saker falcon ( Falco cherrug ), the lanner ( Falco biarmicus ) and the laggar falcon ( Falco jugger ). These four species are genetically indistinguishable from one another. It is a matter of morpho-species that have so far hardly been genetically differentiated and whose radiation is of recent evolutionary history.
The species of origin is probably the Lanner falcon, which today is mainly found in large parts of Africa. It is from there that the spread should also have taken place. Therefore, a union in a superspecies Hierofalco is proposed for these four forms .
Phylogeny of some falcon species:
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Man and Gyrfalcon
Gyrfalcons and falconry
The gyrfalcon has long been one of the most valued birds of prey in falconry. Genghis Khan received tribute payments in the form of gyrfalcons from various clans. After the defeat of the crusade army at Nikopolis in 1396 , King Sigismund and twelve white gyrfalcons freed Jean de Nevers from Turkish captivity.
Friedrich II was an avid falconer. In his book on falconry, he devotes a chapter to the gyrfalcon and describes it as the best of all birds of prey. As early as 1378 there was a trading house in Lübeck in which gyrfalcons from Norway were trained for falconry and were sold in Nuremberg , Venice and even Alexandria , among other places . Between 1731 and 1793, the Danish royal court had almost 5,000 gyrfalcons delivered from Iceland to be sent as diplomatic gifts to almost all European royal courts. In Russia all gyrfalcons belonged exclusively to the tsar and the trappers who caught gyrfalcons on behalf of the tsar were provided with a special decree that ensured their supply of food and shelter on the way to the fishing areas. The Russian tsars also regularly used gyrfalks as a diplomatic gift: Boris Godunov sent gyrfalcons to the Shah of Persia and the Chinese emperor, for example.
Even in the era of National Socialism attempts took place to locate white gyrfalcon in Germany. In 1938, the funded Hermann Goering Foundation and the Empire Jägerhof "Hermann Goering" the Herdemerten-expedition to Greenland to West Greenland. The primary aim of the expedition was to study the Greenlandic gyrfalcon. The expedition leader Kurt Herdemerten brought five living white specimens back to Germany, for their acclimatization and research he set up the polar experimental station " Goldhöhe " in the Giant Mountains at the end of 1938 . At the end of the war, the research facility and the birds were lost.
Gyrfalcons in falconry today
The enthusiasm for falconry, which was cultivated as the most elegant form of hunting in numerous aristocratic residences, continued in Europe until the beginning of the 19th century. Since then, the number of hawks held in captivity, and with it that of gyrfalcons, has steadily declined. Today the focus is on North America and above all the countries in the Middle East. The need for gyrfalcons in western countries is apparently met by the breeding of captive falcons. Only in Alaska can up to ten gyrfalcon cubs be removed from the nests of wild falcons every year. However, the animals may not be exported abroad or to any other US state. Gyrfalcons can also be caught in Canada with an official permit. There are also plans to issue the Inuit in northern Canada with a permit to catch gyrfalcons in return for a payment of Canadian dollars. In the Middle East, falconry has traditionally enjoyed a high status, where very high prices are still paid for white and black gyrfalcons. Due to their susceptibility to heat, gyrfalcons are unsuitable for falconry in the Middle East. They are considered "tuyur majlis" (living room falcons), which are only for show.
As before, because of the monetary value of the birds, nests are illegally robbed or animals are caught. These problems occur in all countries where gyrfalcons breed. Poaching is particularly widespread in Russia, where it has also increased significantly since 1980. The sharp decline in white color morphs between 1980 and 1999 on the Kamchatka Peninsula is mainly attributed to poaching.
literature
- Lothar Ciesielski: The Gyrfalke - Falco rusticolus L. (= Die Neue Brehm-Bücherei. Volume 264). Westarp Sciences, Hohenwarsleben 2007, ISBN 978-3-89432-198-7 .
- Theodor Mebs : Birds of prey in Europe. Biology. Existing conditions. Existence risk. Kosmos nature guide, Stuttgart 1989.
- Benny Génsbøl, Walther Thiede: Birds of prey - All European species, identifiers, flight images, biology, distribution, endangerment, population development. BLV Verlag, Munich 1997, ISBN 3-405-14386-1 .
- GP Dementiew, NN Gortchakovskaya: On the Biology of the Norwegian Gyrfalcon. In: Ibis. 4, 1945, pp. 559-565.
- F. Nittinger, E. Haring, W. Pinsker, M. Wink, A. Gamauf: Out of Africa? Phylogenetic relationships between Falco biarmicus and the other hierofalcons (Aves: Falconidae). In: Journal of Zoological Systematics and Evolutionary Research. Volume 43, No. 4, Nov 2005, pp. 321-331. Blackwell Publishing Oxford, ISSN 0947-5745 .
- Eugene Potapov, Richard Sale: The Gyrfalcon . T & AD Poyser, London 2005, ISBN 0-7136-6563-7 .
- Richard Sale: A Complete Guide to Arctic Wildlife. Christopher Helm Publisher, London 2006, ISBN 0-7136-7039-8 .
- WEC Todd: Birds of the Labrador Peninsula and adjacent areas . Toronto University Press, Toronto 1963.
- Walter Bednarek: Birds of prey - biology, ecology, determination, protection . Verlag J. Neumann-Neudamm, Melsungen 1996, ISBN 3-7888-0837-3 .
Web links
- Falco rusticolus in the endangered Red List species the IUCN 2008. Posted by: BirdLife International, 2008. Accessed on January 1 of 2009.
- Recordings from the great outdoors at www.fokus-natur.de
- Video: Falco rusticolus (Falconidae) - rearing the young . Institute for Scientific Film (IWF) 1980, made available by the Technical Information Library (TIB), doi : 10.3203 / IWF / E-2561 .
- Feathers of the gyrfalcon
Individual evidence
- ↑ a b Bednarek, p. 144.
- ↑ Potapov and Sale, pp. 64f.
- ^ Lothar C. Ciesielski: The gyrfalcon. Falco rusticolus. (= The new Brehm library, Volume 264). 1st edition. Westkarp Sciences, Hohwarsleben 2007.
- ↑ see for example Génsbøl and Thiede, pp. 225 and 374 or Mebs, p. 432.
- ↑ Todd: "Birds of the Labrado Peninsula and adjacent areas", 1963.
- ^ Potapov and Sale, p. 60.
- ↑ Potapov, p. 23, Sale p. 157 and Mebs, p. 432.
- ↑ For example, the gray-brown nominate form “Falco rusticolus rusticolus”, whose distribution area was seen in Scandinavia and Northern Russia, and the light gray form “Falco rusticolus islandus” with Iceland as the distribution area.
- ^ F. Nittinger, E. Haring, W. Pinsker, M. Wink, A. Gamauf: Out of Africa? Phylogenetic relationships between Falco biarmicus and the other hierofalcons (Aves: Falconidae). In: Journal of Zoological Systematics and Evolutionary Research. Volume 43, No. 4, Nov 2005, pp. 321-331. Blackwell Publishing Oxford. ISSN 0947-5745
- ↑ see also Potapov and Sale, p. 43.
- ↑ For a more detailed description of the distinguishing features between gyrfalcon and other similar species see p. Génsbøl and Thiede, p. 376.
- ↑ a b Potapov and Sale, p. 68.
- ↑ a b c Sale, p. 156.
- ↑ Potapov and Sale, pp. 68f.
- ↑ Potapov and Sale, p. 70.
- ↑ For a detailed presentation of the previously published Russian breeding records see Potapov and Sale, pp. 70–76.
- ↑ Génsbøl and Thiede, S. 227th
- ↑ a b c d Mebs, p. 436.
- ↑ Potapov and Sale, pp. 113 and 140f. For a graphic representation of the breeding cycle of ptarmigan and gyrfalcon see p. 144.
- ^ Potapov and Sale, p. 149.
- ^ Potapov and Sale, p. 148.
- ^ Mebs, p. 434.
- ^ Potapov and Sale, p. 191.
- ↑ Potapov and Sale, p. 108.
- ↑ Potapov and Sale, pp. 184ff and 187f
- ^ Potapov and Sale, p. 189.
- ↑ a b c Bednarek, p. 146.
- ↑ a b Sale, p. 157.
- ^ Potapov and Sale, p. 161.
- ^ Potapov and Sale, pp. 168f and 144.
- ↑ Potapov and Sale, p. 169 and p. 217ff.
- ^ Potapov and Sale, p. 169.
- ^ Mebs, p. 433.
- ↑ Potapov and Sale, pp. 128f.
- ↑ Potapov, p. 134. Potapov reports on a gyrfalcon who observed a group of red grouse 400 meters away from a raised hide. As soon as these disappeared behind a bump in the ground, he followed the ptarmigan. It only flew about 1.5 meters above the ground and hit one of the ptarmigan behind the bump in the ground before it could even touch the ground.
- ↑ Potapov and Sale, pp. 130 f.
- ↑ Potapov and Sale, p. 139. These figures were obtained for Icelandic gyrfalcons. There, a Ptarmigan, including feathers and bones, weighs an average of 537 grams
- ^ Mebs, p. 435.
- ↑ Génsbøl and Thiede, S. 226th
- ↑ Potapov and Sale, pp. 81-85.
- ↑ Mebs, p. 434. This number is based on a very conservative estimate of 100 to 200 breeding pairs in European Russia. Individual Russian ornithologists, however, estimate the population at 700 to 1,000 pairs
- ^ 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. 137.
- ↑ Nittinger et al. (2005)
- ↑ Potapov and Sale, p. 200.
- ^ Potapov and Sale, p. 231.
- ↑ Potapov and Sale, p. 232.
- ↑ Potapov and Sale, p. 212.
- ↑ Kurt Herdemerten: Jukunguaq. The Greenland Book of the Hermann Göring Foundation. Georg Westermann publishing house, Braunschweig 1939.
- ↑ a b Potapov and Sale, p. 235.
- ^ Potapov and Sale, p. 233.
- ^ Potapov and Sale, p. 215.
