rook

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rook
Rook (Corvus frugilegus frugilegus)

Rook ( Corvus frugilegus frugilegus )

Systematics
Order : Passerines (Passeriformes)
Subordination : Songbirds (passeri)
Superfamily : Corvoidea
Family : Corvids (Corvidae)
Genre : Ravens and Crows ( Corvus )
Type : rook
Scientific name
Corvus frugilegus
Linnaeus , 1758

The rook ( Corvus frugilegus ) is one of the four European species of the genus Corvus from the family of corvids (Corvidae).

The large crow with a distinctive beak and shiny metallic black plumage is common with the nominate form C. frugilegus frugilegus in a wide belt from Western Europe to the steppes of the Altai region. The occurrence of the second subspecies, C. frugilegus pastinator , adjoins that of the nominate form to the east and extends to the Pacific coast . It is slightly smaller than the nominate form and its plumage shimmers rather reddish purple.

Appearance

The rook can hardly be mistaken for old age. Young birds can be confused with the almost equally large carrion crow ( C. corone corone ). The plumage of the strong rook, about 46 centimeters tall, is uniformly black with a slightly reddish sheen. Depending on the incidence of light, the crown and neck shimmer greenish or purple-metallic. The base of the beak of the adult birds is bare and gritty-whitish, that of the young birds is still feathered. The beak is pointed, the upper beak curved less downward at the front and slimmer than that of the carrion crow. As with the carrion crow, the throat pouch, which is used to transport food, is located below the beak. In flight , the rook can be distinguished from the carrion crow by its slightly longer and deeper-fingered wings. Their flight seems easier, the wing beat is a little faster than with C. c. corone . The sexes differ neither in color nor in size; the young birds take on the appearance of the adult birds at around eight months.

voice

As a socially living species, the rook is very shouting and has a large number of vocalizations, some of which are difficult to distinguish from those of the carrion crow. The most common sound is "Kah" or "Krah", which can sound quite variable; it is often used in the ritual bowing of welcoming partners. In aggressive situations this sound is longer and higher: "krääääh". In addition, especially in spring, a quiet, cooing chatter is embedded in the longer cawing sounds. The young birds and nestlings also call very loudly, they can be heard squeaking. Later one hears a piercing "Rrrah" from them.

distribution

Distribution of the rook green : annual birds or partial migrants / blue : wintering areas orange : mostly migratory birds / orange arrows : known migration directions dark orange : brood distribution of cfpastinator / turquoise : winter distribution of this subspecies

The rook is widespread from Ireland and Great Britain via France and Northern Spain to the steppes of the Altai region. It is missing in southern Switzerland , in large parts of Austria and in Italy . In the north it reaches Denmark and southern Sweden , in the southeast the coasts of the Black and Caspian Seas . In the winter months, the Norwegian coast to central Norway, large parts of the Balkans and most of Turkey are settled. The rook was introduced in New Zealand and even enjoyed protected status there for a long time; today, however, the stocks there are being vigorously decimated again.

habitat

C. frugilegus mostly inhabits open arable and meadow land made up of trees, woods or rows of trees. It is largely dependent on man-made land. Grassland areas, which have a certain proportion of arable land, are particularly favorable for them. She prefers flat or hilly areas, she avoids mountains . The vegetation of their feeding area should not be too high, although if the conditions are favorable they will also look for food in higher grass. She is not afraid of being close to people. Many of their breeding colonies and sleeping places are in the immediate vicinity of human settlements, often also in the parks of large cities, where their loud behavior and their excrement on sidewalks and cars are often perceived as disturbing.

In some major European cities, very large wintering societies have established themselves (e.g. Vienna with around a quarter of a million rooks). The urbanized crows developed various adaptations in terms of behavior, food intake, and daily activity. The distance to flee from humans can be reduced to less than one meter, and the daily activity of city birds is significantly reduced due to the abundant food available. Similar to the black-headed gull , for example , many overwintering populations developed into waste recyclers in waste and landfills. Human feeding has also contributed to the creation of these huge flocks of rooks. The animals show great loyalty to their place. Individuals were observed who had visited the same backyard or the same section of park for years.

Food and subsistence

Rook with walnut

As with all Corvus species, the rook's food spectrum is extremely diverse. Although she prefers plant-based animal foods, the latter is still three-fifths proportionally overweight. Earthworms , different species of snakes , beetles and their stages of development (especially wireworms , the larvae of the click beetles ) and slugs are among the preferred prey animals . In addition, mammals such as field mice , shrews and water voles and occasionally, but rarely, birds and their eggs are consumed. During the winter months the rook goes to carrion , but in much lesser extent than the Crow does. The vegetable diet consists of all kinds of seeds , cereals predominate. In addition, nuts and acorns , and to a lesser extent fruits such as cherries and plums and various wild berries, are also consumed. A high percentage, but not exclusively, of the rearing feed for the young is animal. In contrast to crows and hooded crows, rooks show a kind of fear of water: In order to grab chunks of food from there, they do not wade into the water of shallow puddles, but rather hop on stones protruding from the water. This could also be related to the “feather trousers” on the legs that are typical of rooks.

Rooks tend to walk on flat, short-grassed areas, while carrion crows often have two-legged hopping there. The pointed beak is used as a universal tool when foraging for food, which is used for digging and chopping as well as for probing and poking. Flying insects are also caught by brief flight jumps. The search for food is mainly optically oriented. Vegetable food is picked up or dug up from the ground. Sometimes the rook will also eat corn kernels or sunflower seeds by clinging directly to the plant. Prey animals are pursued only briefly or not at all. In the morning, the daily rhythm of searching is mainly on the surface ( surface feeding ), in the further course of the day the phase of digging and poking begins ( subsurface feeding ), which is finally replaced by the systematic searching of further areas ( areal feeding ).

behavior

rook
rook
Rooks are very social birds. In the evenings they often gather in large swarms and spend the night on tall trees.
Rook breeding colony warning sign

The species begins its activity very early around an hour before sunrise and ends very late, so that around eight hours are available for foraging even in the middle of winter. Rooks are gregarious all year round, breed in sometimes very large colonies and spend the night together on sleeping trees. You have developed an abundance of social behaviors. On the ground, the rook moves measured stepping or hopping, in the air in a powerful oar flight , in which longer stretches of sail are embedded. In the spring you can often see flying games and flying freaks. Games can often be observed between group members, such as dropping and catching objects or swinging on a branch. The behavioral structures between the partners and the other colony members are very diverse and differentiated. The partners greet each other with a kind of parade walk in which the wings are slightly raised. During courtship , there is social feather care, begging for food and long courtship call duets, with both partners usually sitting next to each other with a wide tail, somewhat separated from the others. The roles of males and females only seem to consolidate during these courtship rituals, as the role behavior often changes between the sexes, at least at the beginning of the courtship. Jackdaws ( C. monedula ), more rarely carrion crows ( C. corone ), very often join the overwintering swarms and colonies of rooks.

As with other crows, the exploratory behavior is also very pronounced with C. frugilegus . The resulting behaviors, mostly observed in aviary birds, were also described - in purely anecdotal cases - as the use of tools . Glutz von Blotzheim reports, for example, of the behavior of a young rook, which blocked one of six drainage openings in its aviary so that a "swimming pool" was created. These actions took place more frequently on dry and warm days than on cool and rainy days. A study by British researchers in 2009 demonstrated beyond doubt the ability to use tools on rooks kept in the laboratory. To get a treat from a glass tube, the birds used sticks, the smaller the narrower the glass tube. They also bent the ends of pieces of wire so that they could use these ends as hooks. However, behavior that could be interpreted as tool use has never been described in wild individuals.

In contrast to the carrion crow, dropping nuts from a great height is rarely observed in the rook.

Hike and train

The rook can be both a migratory bird and a resident bird . In general it can be said that the proportion of individuals who are obligatory migratory birds increases from west to east. Most western European birds remain in the breeding area. Around 60% of Central European populations migrate to climatically more favorable areas, with migration distances generally not exceeding 1000 kilometers. In European Russia and east of it, all rooks are migratory birds with migration distances between 1000 and 3000 kilometers. Main migration directions are west and southwest, sometimes north-northwest, but there are also populations with south and southeast migration that overwinter from the Balkans to Greece , Asia Minor to Syria and Iraq . Migrating rooks regularly make their way to the Faroe Islands and Iceland . Most of the rooks stay in the breeding area until the end of September / mid-October and only then start the migration, which can be interrupted by longer rest and rest breaks. The train takes place in large groups, but they are not very cohesive, but smaller train groups seem to form fairly solid units. The adult birds begin to move out at the beginning of February, and it is usually over in the first week of March. In addition to this migratory behavior, rooks are able to carry out so-called weather escapes in very unfavorable weather conditions , which can lead in all directions.

Reproduction and breeding

Egg ( Museum Wiesbaden Collection )

The rook becomes sexually mature at the end of its second year of life, the partners have a monogamous permanent marriage. Nest building begins at the beginning of March, the nest location is usually the crown of deciduous trees in avenues or field trees. The nests are close together, but a distance of less than one meter is rarely exceeded. Nest locations in buildings, bridges and similar places as well as ground broods occur, but are very rare. The nest , which is built by both partners, is a compact structure made of thin, flexible twigs, which is lined with various materials on the inside. Theft of materials within and between colonies is common. The clutch consists of three to six, sometimes up to nine gray-green, indistinctly speckled eggs, and is incubated for 16 to 19 days by the female, who is being fed by the male during this time. Intraspecific brood parasitism occurs at least occasionally, although it is not clear whether the parasitic parents also look after their own clutch. In the case of very large clutches, one must be considered. The nestling period is about a month. For the first ten days, the male does the feeding work alone, then both partners. After becoming independent, the young birds are still looked after by the adult birds for a certain period of time before they join youth groups and roam around in the mostly closer areas. In these youth groups, pairs also take place after one year. Usually there is only one annual brood, only when there is a loss of clutch, second broods and in exceptional cases third broods.

Life expectancy and maximum age

The mortality of rooks in the first and second year of life is between 54 and 59 percent and only then falls slightly. At the beginning of its second year, a crow has an average life expectancy of just under 3.5 years. The losses are primarily caused directly by lack of food or indirectly by diseases caused by it. In exceptional cases, rooks can get quite old. The highest age of a ringed crow to date was found in a dead crow in Great Britain at 22 years and 11 months.

Inventory and inventory trends

Stock and stock development have long been positively and negatively dependent on direct human intervention. By converting the natural landscape into agriculturally used areas, he created the prerequisites for population growth and area expansion, and by direct persecution he limits and endangers the population. Persecution by humans, such as shooting down or poisoning , shooting out nests, felling eyrie or sleeping trees, is the cause of regional declines and fluctuations in stocks. The rook is considered to have caused agricultural damage, although in most cases this assignment does not stand up to scientific scrutiny. Only recently - the rook was bird of the year 1986 - has a certain rethinking started, which has also had a positive effect on the population. Overall, there is a slight westward expansion. One example is the resettlement in Switzerland in the 1960s . The stocks in previously unstably populated regions, such as eastern Austria, also seem to be stabilizing. Across Europe, the population of the species than is S (for English. Secure , dt. Secured ) classified in Austria, Switzerland and the Czech Republic it is on the Red List . The total European population is estimated to be over 10 million breeding pairs.

Damage in agriculture

The rook's damage potential is assessed very differently depending on the perspective. The actual damage intensity differs both seasonally and regionally. However, the actual harmful behavior is always offset by a considerable usage behavior through the consumption of different agricultural and forest pests.

Significant damage can occur if a flock of crows invades a freshly sown field. Early or late individual fields are particularly at risk, especially when the field emerges slowly, such as maize . The crows prefer the germinating seed; To achieve this, they often pull out rows of young plants. Sowing the seeds not too early serves to indirectly prevent damage. A sowing depth of around eight centimeters (instead of two to four centimeters) and the rolling of the seed make it difficult to pull out the small plants, but this prevents optimal field emergence and a good harvest yield . The seeds are usually denatured with an unpleasant-tasting substance , which reduces the amount of food they eat. Crows can be kept away from a field for several days if distraction feeding takes place at the edge of the field or species-specific screams of fear are played electronically. The duration of action of bang devices is shorter . The effectiveness of optical measures such as stretching colored ribbons and hanging dead crows is limited.

Name derivation

The word Corvus used here as a generic name is the Latin name for raven . The Latin word frugilegus is made up of the noun frux, frugis f. = Fruit and the verb legere = collect, pick up together and is used in ancient literature by Ovid ( Metamorphoses 7, 624) in connection with ants . The scientific name can literally be translated as “raven gathering fruit”. The addition to the name pastinator of the subspecies C. frugilegus pastinator literally means “ vineyard worker ”.

Similar species
Rook with a filled throat pouch Carrion crow Jackdaw Common raven
rook
Carrion crow
Jackdaw
Common raven
  • Tapering to a point
  • Beak base with bare skin
  • loosely lying wing feathers
  • flat head
  • Beak base with black feathering,
    beak short and thick, slightly curved
  • tightly fitting feathers
  • Upper head flat
  • Beak base black pinnate,
    beak short and thick
  • Plumage noticeably grayer
  • Eyes white
  • smaller body size
  • Upper head flat, head large
  • Beak base black pinnate,
    beak long, tip curved
  • longer feathers on the throat that
    can be splayed out as a beard

literature

Web links

Commons : Rook  - Collection of images, videos and audio files
Wiktionary: rook  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ↑ HBV Vol. 13 / III. P. 1811
  2. ↑ Christopher D. Bird, Nathan J. Emery: Insightful problem solving and creative tool modification by captive nontool-using rooks. In: Proceedings of the National Academy of Sciences. 106, 2009, p. 10370, doi: 10.1073 / pnas.0901008106 .
  3. ↑ HBV Vol. 13/3 (1994) pp. 1802-1803
  4. ↑ Euring data sheet (English)
This article was added to the list of excellent articles on February 11, 2005 in this version .