25-7-2024 COBH, IRELAND - ROOK (Corvus frugilegus)

The rook (Corvus frugilegus) is a member of the family Corvidae in the passerine order of birds. It is found in the Palearctic, its range extending from Scandinavia and western Europe to eastern Siberia. It is a large, gregarious, black-feathered bird, distinguished from similar species by the whitish featherless area on the face. Rooks nest collectively in the tops of tall trees, often close to farms or villages; the groups of nests are known as rookeries.

Rooks are mainly resident birds, but the northernmost populations may migrate southwards to avoid the harshest winter conditions. The birds form flocks in winter, often in the company of other Corvus species or jackdaws. They return to their rookeries, and breeding takes place in spring. They forage on arable land and pasture, probing the ground with their strong bills and feeding largely on grubs and soil-based invertebrates, but they also consume cereals and other plant material. Historically, farmers have accused the birds of damaging their crops and have made efforts to drive them away or kill them. Like other corvids, they are intelligent birds with complex behavioural traits and an ability to solve simple problems. 

The rook is a fairly large bird, at 280 to 340 g (9.9 to 12.0 oz) adult weight, 44 to 46 cm (17 to 18 in) in length and 81 to 99 cm (32 to 39 in) wingspan. It has black feathers that often show a blue or bluish-purple sheen in bright sunlight. The feathers on the head, neck and shoulders are particularly dense and silky. The legs and feet are generally black, the bill grey-black and the iris dark brown. In adults, a bare area of whitish skin in front of the eye and around the base of the bill is distinctive, and enables the rook to be distinguished from other members of the crow family. This bare patch gives the false impression that the bill is longer than it is and the head more domed. The feathering around the legs also appears shaggier and laxer than the similarly sized carrion crow, the only other member of its genus with which the rook is likely to be confused. Additionally, when seen in flight, the wings of a rook are proportionally longer and narrower than those of the carrion crow. The average lifespan is six years.

The juvenile plumage is black with a slight greenish gloss, except for the hind neck, back and underparts, which are brownish-black. The juvenile is superficially similar to a young crow because it lacks the bare patch at the base of the bill, but it has a thinner beak and loses the facial feathers after about six months.

Western rooks are resident in the British Isles and much of north and central Europe but vagrant to Iceland and parts of Scandinavia, where they typically live south of 60° latitude. They are found in habitats that common ravens dislike, choosing open agricultural areas with pasture or arable land, as long as there are suitable tall trees for breeding. They generally avoid forests, swamps, marshes, heaths and moorland. They are in general lowland birds, with most rookeries found below 120 m (400 ft), but where suitable feeding habitat exists, they may breed at 300 m (1,000 ft) or even higher. Rooks are often associated with human settlements, nesting near farms, villages and open towns, but not in large, heavily built-up areas. The eastern subspecies in Asia differs in being slightly smaller on average, and having a somewhat more fully feathered face. In the north of its range the species has a tendency to move south during autumn, and more southern populations are apt to range sporadically.

 

The rook is a very social bird; in the evenings they gather in large flocks, often in thousands.

Rooks are highly gregarious birds and are generally seen in flocks of various sizes. Males and females pair-bond for life and pairs stay together within flocks. In the evening, the birds often congregate at their rookery before moving off to their chosen communal roosting site. Flocks increase in size in autumn with different groups amalgamating and birds congregating at dusk before roosting, often in very large numbers and in the company of jackdaws. Roosting usually takes place in woodland or plantations, but a small minority of birds may continue to roost at their rookery all winter, and adult males may roost collectively somewhere nearby. The birds move off promptly in the morning, dispersing for distances of up to 10 km (6 mi).

Large groups of rooks (in breeding colonies or night roost sites) can contribute to changes in soil properties. The amount of ornithogenic material in these soils is very high.

Foraging mostly takes place on the ground, with the birds striding about, or occasionally hopping, and probing the soil with their powerful beaks. Flight is direct, with regular wingbeats and little gliding while in purposeful flight; in contrast, the birds may glide more extensively when wheeling about in leisure flight near the rookery. In the autumn, flocks sometimes perform spectacular aerial group flights, including synchronised movements and individual antics such as dives, tumbles and rolls.