[order] Passeriformes | [family] Corvidae | [latin] Corvus frugilegus | [UK] Rook | [FR] Corbeau freux | [DE] Saatkrähe | [ES] Graja Común | [IT] Corvo nero | [NL] Roek

Roek determination

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Quite large and elegant crow, with slender bill, bare, and pale face, and characteristic "baggy trousers" above legs. Slightly smaller than Carrion Crow, proportionately smaller head with steeper forehead, and seemingly deeper body due to loose flank feathers cloaking thighs. In flight, more splayed wing-tips and rounder tail. Plumage black with heavy floss. Highly sociable at all times of year. Voice distinctive. Sexes similar, no seasonal variation.

Breeds only in boreal and temperate middle latitudes of west Palearctic, in both continental and oceanic lowlands, but absent from warmer regions, except in winter. Strong winds, ice, and snow are avoided but rain and mist are tolerated. Range excludes most mountains regions.

Corvus frugilegus is a widespread resident across much of Europe, which accounts for less than half of its global range. Its European breeding population is extremely large (>10,000,000 pairs), and increased between 1970-1990. Although the species declined in a few countries during 1990-2000, most European populations were stable or increased. The trend of the key population in Russia was unknown, but the species was probably stable overall.

Primarily a bird of agricultural landscapes, foraging almost exclusively on ground, only rarely in trees, taking defoliating caterpillars or swarming beetles in spring. Forages on both pasture and arable land. In spring, feeds on newly-sown cereal or follows plough, searching for exposed invertebrates, particularly larvae, then moves to pasture, notably where water-table high. Invertebrates, mainly beetles and earthworms, plant material, small vertebrates, carrion, and scraps of all kinds. Rooks also like areas where there are walnut trees and agricultural crops, especially cereals. They avoid the bush and forested areas so are no real threat to our native or endemic birds. They prefer to eat insects, earthworms and walnuts but when these become scarce the birds may gather in large flocks and eat maize, wheat, barley, peas or beans.
The habit of storing walnuts is of special interest. Ripening nuts are picked from a tree and carried some distance and buried intact in open paddocks, in a tuft of grass or between clods of ploughed soil. The birds return in autumn to recover the stored nuts, which they hold on the ground with one foot while hammering a hole through the hard shell to extract the kernel.

This species has a large range, with an estimated global Extent of Occurrence of 10,000,000 km². It has a large global population, including an estimated 20,000,000-35,000,000 individuals in Europe (BirdLife International in prep.). Global population trends have not been quantified; there is evidence of a population decline (Madge and Burn 1993, Snow and Perrins 1998), but the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e. declining more than 30% in ten years or three generations). For these reasons, the species is evaluated as Least Concern. [conservation status from birdlife.org]

Breeding starts mid March to end of April in Britain, mid April to mid May in Central Russia. Nest site, in topmost crown of high tree, exceptionally on horizontal branch or against trunk. Tree almost always in rather isolated groups. The nest is a fairly regular hemisphere, sometimes slightly flattened. Foundation of sticks and large twigs, inside which layer of thin pliable twigs very often of birch and willow, many with leaves, followed by compact mass of rootlets, moss, mixed with clay to form small cup, which is lined with grass, moss, stalks, feathers , leaves or fpor example paper. 2-6 eggs are laid and incubation lasts 16-18 days and is done by female only.

Resident to migratory, with more birds migrating in cold winters. Winters in Eurasia, within and south of breeding range. Migrates by day in flocks, often following leading-lines such as coastlines and river valleys and frequently accompanied by Jackdaws. Ringing data have revealed winter quarters of particular populations in unusual detail, and show that mountain ranges act as barriers, thus affecting winter distribution. Adults tend to move less far than juveniles.
British and Irish birds almost entirely resident; juveniles may disperse from natal area in 1st winter, but rarely move more than 100 km. Spanish birds also resident. Chiefly resident in France, though some birds from north migrate 100-400 km. Partial migrant in Low Countries, Germany, and Scandinavia. Chiefly migratory in Poland and Czechoslovakia. In FSU, present all year in southern areas, though some southern birds may move south in colder winters; in migratory areas further north, some birds stay irregularly in certain years. Within Europe, migrants head between west and south, so winter numbers far higher than summer in western Europe, and many migrate also to central and eastern Europe.
Following post-breeding dispersal, autumn departure begins September, with main movement October-November. Arrivals in Britain and France are late September to November, and wintering birds reach Rhône-Alpes (southern France) in last third of October. Hard-weather movements sometimes reported mid-winter. Return movement is early, February-March, exceptionally from January. Winter visitors leave Britain mid-February to 3rd week of April, and Rhône-Alpes by end of March or beginning of April. Swedish breeding birds return February-March; arrive on breeding grounds in Moscow region 2nd half of March.