Gray woodpecker
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Gray woodpecker ( Picus canus ) |
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| Gmelin , 1788 |
The gray-headed woodpecker ( Picus canus ) is a species of bird from the family of woodpeckers (Picidae). It is next to the much more common green woodpecker ( Picus viridis ) and the Iberiengrünspecht ( Picus sharpei ), the third representative of the so-called "Erdspechte" in Europe. Its distribution area extends over large parts of the central and eastern Palearctic , eastward to the Pacific coast.
The gray woodpecker is much more demanding in terms of its habitat than the green woodpecker. He prefers old mixed deciduous forests with a high proportion of dead wood. The species feeds primarily on ants, although it is not as dependent on this family of insects as the green woodpecker. The breeding cave is usually created in dead or at least severely damaged trees.
The Southeast Asian gray woodpeckers , those from the Himalayan region and those from Sumatra , which have long been regarded as subspecies , have been viewed as separate species Picus guerini and Picus dedemi since 2014 , so that currently (as of 2016) three subspecies are distinguished.
The population development of the species is negative in most areas for which more detailed estimates are available. The IUCN assesses the entire population as safe, mainly due to the very large distribution area .
Appearance
The body length of the gray woodpecker is 28–33 centimeters, its weight is between 110 and 206 grams. The birds of the subspecies P. c. jessoensis are usually somewhat larger and heavier than individuals of the nominate form . On average, it is slightly smaller and lighter than the green woodpecker. However, this size difference can hardly be ascertained by field ornithology without a direct comparison. Approximately the size of the species corresponds to that of a turkey dove .
Gray woodpeckers are fairly uniformly matte olive green on top. Over the neck towards the head this color changes into a light gray, the head looks light gray. The typical woodpecker face and crown drawings are small and not very noticeable. The red coloration is reduced to a small spot in the forehead area in the male, only a relatively indistinct rein strap and a slightly noticeable streak of beard are black. The beak is dark and very slightly curved upwards, the iris of the eyes is also dark and, depending on the incidence of light, sometimes shimmers slightly reddish. Neck markings are completely absent in the subspecies of the canus group widespread in Europe and West Asia . In contrast, the neck of the subspecies of the guerini group is black. The back and rump are lighter than the back plumage and usually have a rich, dull yellow-green. The tail, which is slightly longer than that of the green woodpecker, is colored like the dorsal plumage, but some of the control feathers are a little lighter and also irregularly banded in light brown-yellow, so that the tail appears somewhat speckled overall. The underside of the woodpecker is uniform and dull pale yellow without drawing, the throat is very light, sometimes almost white. When sitting, the dark gray to black, clearly lightly banded hand wings form a dark-light marked, mostly conspicuous wing edge.
The sexes differ quite significantly from one another. In the female, the small red apex plate of the male is missing, mostly in them this part of the plumage is a little darker gray or very light gray-black striped. The black markings (reins and beard stripes) are also narrower, shorter and more dull in color. Overall, the plumage of the female is paler and duller. The sexes do not differ in size and weight.
Even in the plumage of youngsters there is a very clear sexual dimorphism . Juvenile males already show hints of the red crown plate and the black facial markings, their plumage is greenish-brown and indistinctly dark banded on the underside. Juvenile females, on the other hand, are rather dull green-gray with no signs of drawing;
flight
Like green woodpeckers, gray woodpeckers fly in a very fast, wavy arc flight. The body is stretched out, the wings are flapped a few times in quick succession and then - in the trough of the waves in the course of the flight - placed close to the body. Gray woodpeckers fly up more frequently than green woodpeckers. While these also cover longer distances by hopping, gray woodpeckers usually fly over shorter changes of location.
Differentiation gray woodpecker and green woodpecker
The gray woodpecker is similar to the green woodpecker, but there are good distinguishing features that can also be used in field ornithological terms. In the green woodpecker, both sexes have extensive red forehead and neck markings, in the gray woodpecker only the male has a small red forehead crown plate. The green woodpecker is light-eyed, the entire cheek area of this woodpecker is black. In the dark-eyed gray woodpecker, only small areas (rein tape, narrow beard strip) are black. The bright olive-green-yellow green woodpecker is a conspicuous, present bird, while the gray woodpecker, which is similar in color, but has a duller color, lives mostly very hidden and inconspicuous, without being shy as the green woodpecker. Although there is no overlap in the distribution of the species in this area, the green woodpecker of the Iberian Peninsula ( Picus viridis sharpei ) is very similar to the gray woodpecker . With these, too, the face mask is reduced to a short stripe of rein or beard, the cheek area appears gray overall. The red forehead and neck badges, on the other hand, are worn by both sexes.
The territorial calls of the two species are clearly distinguishable, but it must be noted that green woodpeckers often call like gray woodpeckers in regions where the gray woodpecker does not occur .
voice
The vocalizations of the green woodpecker and gray woodpecker are very similar. However, the far-reaching territory song of the gray woodpecker is more melodic and purer than the explosive laugh of the green woodpecker. The sound series consisting of ten to 15 individual elements ( klü-klü-klü ... kü ... kü ... kü (kö) .. ) falls in pitch and becomes slower with larger syllable spacing. The stanza seems a bit melancholy, gloomy, towards the end it becomes quieter and dies . The female's territorial singing is very similar, but a little quieter and not so full of melody, but more croaking and usually shorter. The district songs can be heard from the end of February, and earlier in particularly mild winters. The highest singing intensity is in March, after which these woodpeckers behave acoustically very unobtrusively. The Reviergesang serves both to demarcate the territory and to maintain the territory as well as to recruit partners. In addition, the male communicates with the female with soft djück calls, to which the female responds either hoarsely or loosely, depending on the situation . The importance of this differentiation is not known.
In addition to these partner-related vocalizations, both sexes, but more often the male, can hear aggressive sounds. Individual, sharp kük calls dominate, which are lined up with increasing excitement and continued with kek . An individual kük also has a warning function, because barring young immediately fall silent after this call from a parent. The individual drum activity of the gray woodpecker is very different, but they drum more often than green woodpecker. The beat frequency is about 20 beats per second, a vortex can contain up to 40 beats, i.e. last two seconds. Both sexes drum, but the female drum less frequently and usually also quieter and shorter. Gray woodpeckers often use the same, well-resonating drum pads for years - these drum locations can be located quite far from the brood cavity. Because of the particularly favorable response, the gray woodpecker often uses metal covers on masts or roofs as a drum base.
Voice examples
distribution
The gray woodpecker is distributed over large parts of central, northern and southeastern Europe, as well as in a wide belt south of the boreal coniferous forest across Asia to the Pacific coast, Sakhalin and Hokkaidō . Essentially, the northern border of the distribution area lies in the transition area between closed coniferous forest and loosened mixed deciduous forest, the southern border runs in those regions in which the tree steppe changes into treeless shrub and bush steppe. The species reaches its greatest racial differentiation in East Asia and colonizes the Korean Peninsula from Manchuria to the south , large areas of eastern China and rear India, the mountain forests of the Malay Peninsula and higher areas on Sumatra . It is unclear whether the species also occurs in Borneo . Some populations have penetrated far into the mountain valleys and foothills of the Himalayas .
In Europe, the nominate form Picus canus canus breeds from western France in a wide belt eastwards to the Urals . Large areas in central Scandinavia and in Central, Eastern and Southeastern Europe are settled. There is contradicting information about the population in Turkey, but the species probably breeds in several (hundred?) Pairs in the low mountain ranges of the Pontic Mountains . The species does not occur in the North German Plain , on the British Isles and on the Iberian Peninsula . The Mediterranean islands are also not populated. In Italy, the gray woodpecker only breeds in the far north.
The gray woodpecker is not common anywhere within its extensive and extensive distribution area. The main distribution centers of this species are in the Eastern Palearctic.
habitat
The gray woodpecker breeds in richly structured landscapes that have at least small proportions of hardwood. It is more closely tied to the forest than the green woodpecker and, in contrast to this, also occurs in the interior of large, closed forests. Overall, its habitats are very different. Loosened mixed deciduous forests with diverse border structures are preferred, such as clearings, windthrow areas, young growth stands, avalanche lanes or large boulders scattered in between, which offer sufficient trees for creating nesting and sleeping caves as well as drum trees as well as sections rich in dead wood and open spaces for food acquisition. The gray woodpecker finds such landscape structures in Europe above all in alluvial forest areas and in low mountain ranges that are only extensively managed for forestry. However, it can also colonize secondary habitats such as parks, orchards, cemeteries or golf courses and occur there in a relatively narrow space together with the green woodpecker. Although the gray woodpecker seems to prefer to colonize beech forests in some areas of Central Europe, no clear deciduous tree preferences can be determined overall. In winter, coarse-barked trees such as poplars or oaks are often sought out for food. Coniferous forests are not generally avoided either, in Vorarlberg the species breeds in mixed pine forests and in old larch stands, an isolated Greek population in the Oita Mountains colonizes pure fir stands ( Abies cephalonica ).
In Europe the gray woodpecker is preferred in habitats of the colline and submontane levels. In its Asian areas of distribution, breeding sites at over 3000 m are known, the East Asian gray woodpeckers are almost exclusively breeding birds of the mountain forests. However, where the species finds undisturbed living conditions and sufficient food supply, it also breeds in lowland areas. In the poplar and alder galleries of the Danube Delta , for example, the population densities are very high, and in Germany, too, some extensive riparian forests are good gray-woodpecker areas.
In Asia, the species inhabits different forest types, whereby those with deciduous tree species are apparently preferred. In the Himalayas, gray woodpeckers rise to heights of over 3000 m , but the focus of brood distribution is below these altitudes. Bamboo trees are also occasionally colonized in East Asia. In winter, gray woodpeckers can be found in a wide variety of landscape structures, including in reed areas.
There are only a few reliable figures from Central Europe on settlement densities and area sizes. In optimal habitats, comparatively high densities with up to ten breeding pairs per square kilometer were found. Most suitable areas are, however, significantly less populated. The average range of action of a gray woodpecker pair in Central Europe is around one to two square kilometers.
Systematics
The gray woodpecker is a member of the Picus genus , to which 14 other species belong. Only the Iberian green woodpecker ( Picus sharpei ) and the Atlas green woodpecker ( Picus vaillantii ) have penetrated further into the west and south-west Palearctic respectively. The radiation originated in Southeast Asia, where most of the other species of this genus are still found today.
Green woodpecker, gray woodpecker, Iberian green woodpecker and Atlas green woodpecker are evolutionarily young species. Populations of a common ancestral species were probably isolated during the last Ice Age , the Worm Ice Age . Only after the ice had melted did the species come into contact with one another again. The genetic differentiation between the three species may be even more recent.
The two species Picus guerini and Picus dedemi, which have long been regarded as conspecific, are sister species , the green woodpecker is very closely related.
Currently (2016) three subspecies are described:
- Picus canus canus Gmelin, JF , 1788 : described above. Europe to Western Siberia. In western Siberia there is a broad transition area between the nominate form and P. c. jessoensis .
- Picus canus jessoensis Stejneger , 1886: Central and Eastern Siberia; Sakhalin, Hokkaido; south to northern China. Slightly larger and heavier on average. Overall brighter; Gray parts predominate, less green.
- Picus canus griseoviridis ( Clark , 1907): Korea. Smaller and darker than P. c. jessoensis ; larger proportion of green.
A number of other subspecies have been described, but as of 2016 they are regarded as individual coloring variants and are not recognized as subspecies.
The International Ornithological Committee also conducts:
- Picus canus kogo ( Bianchi , 1906) occurs in central China .
- Picus canus guerini ( Malherbe , 1849) occurs in north-central and east-central China.
- Picus canus sobrinus Peters, JL , 1948 is widespread in southeastern China and northeastern Vietnam .
- Picus canus tancolo ( Gould , 1863) occurs in Hainan and Taiwan .
- Picus canus sordidior ( Rippon , 1906) is widespread in southeastern Tibet and southwestern China to northeastern Myanmar .
- Picus canus sanguiniceps Baker, ECS , 1926 occurs in northeastern Pakistan to northern India and western Nepal .
- Picus canus hessei Gyldenstolpe , 1916 occurs in Nepal and northeast India as far as Myanmar and Indochina .
- Picus canus robinsoni ( Ogilvie-Grant , 1906) occurs in western Malaysia .
- Picus canus dedemi ( van Oort , 1911) is widespread in Sumatra .
P. c. griseoviridis is used there as a synonym for P. c. jessoensis seen.
Hybridizations
There is some evidence of mixed breeds between gray and green woodpeckers, but they seem to be extremely rare. The female partner was apparently always a gray woodpecker. The young, about whose fertility nothing is known, resemble a gray woodpecker more closely in the plumage, but have a red crown, a reddish nape and a light iris; some were also strikingly dark in color.
food
The gray woodpecker is a somewhat less specialized ant hunter than the green woodpecker . In his nutritional strategy he forms an intermediate link between many species of the great spotted woodpecker ( Dendrocopos ) and the other species of the genus Picus, which are mostly specialized in ants . This less strict orientation of the gray woodpecker on ant food also allows the two native Picus species to appear sympatric in many areas and to breed very close to each other at distances of about 100 meters.
Nevertheless, especially in spring and summer, ants and their developmental stages form the main component of the gray woodpecker diet. Especially wood ants ( Formica sp.), Garden ants ( Lasius sp.) And representatives of the host ant , in particular those of the genus Myrmica dominate the food spectrum. In addition, caterpillars , crickets and various bark and wood-dwelling beetle larvae as well as flies and lice play an important role as prey. In late autumn and winter, gray woodpeckers regularly consume substantial amounts of vegetarian food, such as various berries and fruits.
behavior
Activity and comfort behavior
The activity range of the gray woodpecker extends from sunrise to sunset. Females are usually active longer and often don't return to their sleeping caves until late at dusk. Within this activity period, gray woodpeckers take very different lengths of time and irregular rest and comfort breaks in their temporal distribution. Gray woodpeckers use several sleeping dens and change them more often than the green woodpecker.
Very little is known about the comfort behavior of the species. So far, gray woodpeckers have only rarely been seen bathing or drinking. On the other hand, gray woodpeckers were seen more frequently both passively and actively .
Territorial and aggressive behavior
Gray woodpeckers are extremely distant birds outside of the breeding season . However, breeding partners can occasionally also be found together outside the breeding season. The greatest proven proximity of neighboring breeding caves was 1.25 kilometers. Gray woodpeckers claim territories of different sizes, which under the most favorable conditions can only be around ten hectares, but usually exceed this size several times over. The winter areas in particular cover a few square kilometers. The area is marked by shouts, but invading conspecifics are not attacked directly. Key points, on the other hand, are defended directly and aggressively against conspecifics and other birds. These can be particularly cheap places to eat (anthills, tree stumps rich in insects, frequented ant roads), resting and drumming areas as well as sleeping caves within the area. Such arguments can lead to occasionally fatal hacking fights. Both sexes usually react to sound mock-ups with answers from a greater distance, but occasionally also with closer proximity and closer inspection of the source of the disturbance. When humans disturb the nest, gray woodpeckers usually keep very quiet, often fleeing at the first signs of disturbance. They provide intensive protection against potential enemies and often remain completely motionless for a long time on the side of the trunk facing away from the intruder.
In disputes about a breeding cave, the gray woodpecker is subject to the green woodpecker, but also evades relatively quickly against other cave-demanding birds such as stock pigeons or starlings .
Food acquisition
The food is mainly sought and consumed on the ground. Usually the ants are collected directly from the ground, from a tree trunk or a trunk, and more rarely he pokes holes in rotten wood himself. The tongue serves more as a liming rod than as a harpoon when ingesting food. Wood-dwelling insects are tracked under the bark, in the process he removes loose parts of the bark and pokes insect larvae with boring movements from rotting wood stumps. In winter, fruits and berries are picked up from the ground as well as directly from the trees and bushes, with gray woodpeckers occasionally balancing hanging upside down from a branch. The foraging flights lead gray woodpeckers relatively far away from the breeding cave, distances of more than one kilometer were regularly recorded. In severe winters, gray woodpeckers often benefit from the activities of the black woodpecker ( Dryocopus martius ), which, even at low temperatures and with high snow cover, can open anthills or get to wood-dwelling insects through its extensive chopping. Gray woodpeckers regularly foraging on rocks and cliffs, occasionally also on buildings, and a little more often than green woodpeckers they visit bird feeders or farms. These are mainly young birds and females, which are evidently driven out of male territories when food is scarce.
hikes
In most of the populations of this species, resident birds predominate . Changes of location are mostly small-scale, with females - probably by necessity - showing greater mobility than males. Breeding birds from higher altitudes expand their territories widely into lower areas. In winter, breeding grounds are often enlarged ten times the area, whereby the former breeding site does not necessarily have to be in the center of the winter area. When food is scarce, females and young birds often have to move to less optimal areas and then appear in the immediate vicinity of settlements and feeding places. When the snow cover is high, the males also move to more favorable areas.
More extensive and seasonally recurring migratory movements apparently take place in northern European and Siberian populations. Some birds, central Swedish birds according to ring findings, migrate for a few 100 kilometers along the coastline of the Baltic Sea to the southwest and return to their breeding grounds in late winter. It is possible that gray woodpeckers from Finland and the Åland Islands regularly fly over the Gulf of Bothnia . Similar migration movements are known from the Central Siberian gray woodpecker.
The general loyalty to the breeding site of the species is also reflected in the mostly short distances of the juveniles . With an average population density and sufficient food and breeding ground resources, young gray woodpeckers usually try to re-establish themselves within a radius of 20 kilometers, dispersion flights of more than 50 kilometers are among the exceptions.
Breeding biology
Courtship and pairing
Gray woodpeckers become sexually mature at the end of their first year of life. They lead a largely monogamous breeding season marriage. Because of the high loyalty to the breeding site of the species, re-breeding should not be uncommon. The courtship begins in early late winter, in Central Europe in mild weather at the end of January. However, it does not peak until late February and early March. It can last well into April, in exceptional cases you can hear the gray woodpecker's calls for territory and courtship until May. The main courtship of the North European and North Asian populations does not begin until mid-March and lasts until June. There is no information available about the breeding season of the Southeast Asian subspecies or those from the Himalayan valleys and foothills.
The main courtship begins with intensive series of calls and drumming, first of the male, after both sexes have been mated. The breeding area is flown over, existing caves are inspected. Occasionally, especially before a copula, the male feeds the female. An essential part of the pair bond is the cave showing and the nesting cave construction. Whether a new cave is built depends on the availability of usable old ones, often black woodpecker caves are adapted or great spotted woodpecker caves are expanded. Gray woodpeckers very rarely breed in nest boxes. Gray woodpeckers build caves themselves in different tree species, whereby beech and oak are preferred , in the alluvial forests poplars , birches and willows . Gray woodpecker caves are also found in linden , alder , elm and ash , and occasionally also in conifers. In secondary habitats, fruit trees, especially cherry and pear trees , are also chosen as cave trees . Both partners work on the breeding and sleeping caves. As a rule, areas of weathering or broken branches are used to make the nesting site. It is not uncommon for the caves to be created not in the trunk but in largely vertical branch sections. The breeding caves are usually at heights between three and five meters. In exceptional cases, they can be placed almost close to the ground or in the crown area of tall trees. The trunk or branch section in which the cave is located is often slightly inclined, so that the entrance hole is protected against rain. The entrance hole itself is round, sometimes slightly oval and measures around five to six centimeters in diameter. Often, however, a crack or gap in the tree also forms the entry point that is barely recognizable from the outside. The breeding caves themselves are on average up to 30 centimeters deep. Like almost all woodpeckers, the gray woodpecker does not bring in any nesting material, but enough wood chips remain in the nest cavity to provide a relatively soft surface.
Clutch and brood
The egg-laying begins a little later than with the green woodpecker, in Central Europe mostly in mid-April, in the Northern European and North Asian breeding areas accordingly later. No information is available about the breeding seasons of the Southeast Asian green woodpeckers. Gorman names four to five eggs as an average, while Glutz von Blotzheim and Bauer put the size of the average clutch at seven to nine eggs. The eggs are usually long-oval, fine-pored, white and shiny and occasionally have a fine yellow or gray sheen. With a mean size of about 27.5 × 20.5 millimeters, they weigh about seven grams. The eggs are laid in the daily rhythm in the early morning. Both sexes only breed intensively after the last egg has been laid, so that the young hatch almost simultaneously after 16 to 17 (14 to 18) days. Gray woodpeckers only breed once a year, nothing is known about subsequent clutches when the clutch is lost.
The boys are fed and warmed by both parents. In the first few days, the insect food is pre-digested, then the food animals are offered in the beak. Some times were virgin females as breeding helpers observed. The nestlings are fully fledged after about 24 to 25 days. Within a week, the entire family leaves the area around the nest box. The lead time always seems to be very short and should occasionally be omitted completely.
Breeding success and maximum age
Although the clutches of the gray woodpecker can be very large, only rarely do more than four young fly out. Freshly fledged young birds are particularly at risk and often have accidents. Little data is available on the life expectancy of wild gray woodpeckers. The maximum age of a ringed bird so far found was five years and four months. In general, however, woodpeckers can occasionally reach a very old age even in the wild. The previously determined maximum age of a green woodpecker was over 15 years.
Inventory and inventory development
The gray woodpecker is one of the species that is very difficult to determine, as single breeders in particular show little call activity. Isolated areas are therefore often overlooked. For this reason, inventory information is subject to considerable uncertainty. In Europe, especially on the north-western border of the distribution area, there has probably been a decline in the population since the 1960s and an associated loss of area. Since the 1990s, however, the gray woodpecker populations seem to be recovering again, probably due to the predominantly mild winter. A slight decline in the population is found worldwide, but it does not meet the criteria for a hazard level. That is why the populations of this woodpecker species are considered secure.
In Europe, the stocks are currently stable or are even increasing slightly in some countries, a fact that may be a sham effect and is only due to the better coverage of this species in recent years. The total European population is estimated at 180,000 to 320,000 breeding pairs. Key deposits are located in the European part of Russia as well as in Romania. About 15,000 pairs breed in Germany, around 2,500 in Austria and around 1,500 in Switzerland. In the Red List of Germany's breeding birds from 2015, the species is listed in Category 2 as critically endangered. There are no summarizing figures on the non-European population.
Since the gray woodpecker prefers undisturbed and pristine forests with natural age structures as well as alluvial forest areas as breeding habitats, the greatest threat to the species lies in the destruction of such habitats.
literature
- Hans-Günther Bauer and Peter Berthold : The breeding birds of Central Europe. Existence and endangerment. 2nd edition, Wiesbaden 1997, ISBN 3-89104-613-8 , pp. 283f.
- Mark Beaman and Steve Madge : Handbook of Bird Identification. Europe and Western Palearctic. Stuttgart 1998, ISBN 3-8001-3471-3 , p. 532.
- Dieter Blume : black woodpecker, gray woodpecker, green woodpecker (= Neue Brehm-Bücherei vol. 300). Magdeburg 1996, ISBN 3-89432-497-X .
- L. Edenius et al .: Winter behavior of the Gray-headed Woodpecker Picus canus in relation to recent population trends in Sweden . Ornis Svecica Vol. 9, 1999: pp. 65-74.
- Urs N. Glutz von Blotzheim (Hrsg.): Handbook of the birds of Central Europe Volume 9. Columbiformes - Piciformes . 2nd, revised edition. Frankfurt am Main 1994, pp. 917-942, ISBN 3-89104-562-X .
- Gerard Gorman: Woodpeckers of Europe. A Study to European Picidae. Chalfont 2004, pp. 57-68 and p. 44; 35, ISBN 1-872842-05-4 .
- Jochen Hölzinger (Ed.): The birds of Baden-Württemberg. Non-Singvögel Vol. 2/3 , Stuttgart 2001, ISBN 3-8001-3908-1 .
- Josep del Hoyo et al .: Handbook of the Birds of the World . Volume 7: Jacamars to Woodpeckers. Barcelona 2002, ISBN 84-87334-37-7 .
- Hans Winkler , David Christie and David Nurney: Woodpeckers. A Guide to Woodpeckers, Piculets, and Wrynecks of the World. Robertsbridge 1995, ISBN 0-395-72043-5 .
Individual evidence
- ↑ a b Winkler, H. & Christie, DA (2016). Gray-faced Woodpecker (Picus canus). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, DA & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (accessed on hbw.com on October 1, 2016)
- ↑ IUCN data sheet
- ↑ Winkler, H. & Christie, DA (2016). Gray-faced Woodpecker (Picus canus). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, DA & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (accessed on hbw.com on October 5, 2016).
- ↑ Gormann (2004), p. 64.
- ↑ Beaman / Madge (1998), p. 532.
- ↑ a b Swiss Ornithological Institute, Sempach.
- ↑ a b c Gorman (2004), p. 61f.
- ↑ Hölzinger (2001), pp. 391–392.
- ↑ James Conwan Greenway: Oriental Forms of Picus canus (PDF).
- ^ IOC World Bird List Falcons
- ^ Eugene M. McCarthy: Handbook of Avian Hybrids of the World . Oxford University Press 2006. ISBN 978-0-19-518323-8 , p. 109.
- ↑ Gorman (2004), p. 59.
- ↑ a b Glutz von Blotzheim (1994), p. 936.
- ↑ Gormann (2004), p. 65.
- ^ Glutz von Blotzheim (1994).
- ↑ Edenius et al. (1999) quoted from Gorman (2004), pp. 62/182.
- ^ Glutz von Blotzheim (1994), p. 930.
- ↑ Gormann (2004), p. 68.
- ↑ Glutz von Blotzheim (1994), p. 931.
- ↑ Gormann (2004), p. 66.
- ↑ Glutz von Blotzheim (1994), p. 934.
- ↑ a b Gorman (2004), p. 67.
- ↑ a b c Blotzheim (1994), p. 935.
- ↑ Euring data sheet
- ↑ Bauer / Berthold (1997), p. 283.
- ↑ factsheet birdlife international (2006).
- ↑ factsheet birdlife europe (2004).
- ↑ Christoph Grüneberg, Hans-Günther Bauer, Heiko Haupt, Ommo Hüppop, Torsten Ryslavy, Peter Südbeck: Red List of Germany's Breeding Birds , 5 version . In: German Council for Bird Protection (Hrsg.): Reports on bird protection . tape 52 , November 30, 2015.
Web links
- Picus canus in the endangered Red List species the IUCN 2008. Posted by: BirdLife International, 2008. Accessed January 2 of 2009.
- Euring Longevity database
- Factsheet birdlife international (2006) (English)
- Factsheet birdlife europe (2004) (English, PDF; 330 kB)
- Information from the Swiss Ornithological Institute in Sempach
- Feathers of the gray woodpecker
