Rook

Name and taxonomy

The scientific name of the rook is Corvus frugilegus. Carl Linnaeus named the bird in 1758 in the tenth edition of his great catalogue. Corvus is Latin for raven, and the second word means fruit gathering. The English name rook comes from the harsh sound the bird makes. Collective nouns for the species include building, parliament, clamour and storytelling.

Two subspecies are recognised. The western rook lives from western Europe to southern Russia and the far northwest of China. The eastern rook runs from central Siberia and northern Mongolia across the rest of Asia. The Altai Mountains divide the two ranges. Eastern birds are slightly smaller and carry more feathering on the face.

Evolution and relatives

The rook belongs to Corvidae, the crow family, inside the huge order of perching birds. Its genus, Corvus, also holds the ravens, the carrion crow and the jackdaw. The carrion crow is the species most often mistaken for it. A rook has longer, narrower wings, a wedge-shaped tail and spread wingtip feathers. Its bill is paler and tapers to a sharper point than a crow's.

Like other crows, the rook has a large brain for its size and solves problems in tests. Unlike the ravens, it feeds and nests in dense groups all year. The bare face is unusual in the family and may reduce soiling while the bird probes soil. Rooks flock with jackdaws through the winter, which suggests the two suit the same fields.

Appearance

The plumage is black throughout, with a gloss that turns blue or bluish purple in sun. Head, neck and shoulder feathers grow dense and silky. An adult is 44 to 46 cm long and spans 81 to 99 cm across the wings. Body weight runs from 280 to 340 g. The legs and feet are black, the bill is grey-black and the iris is dark brown.

The bare pale patch covers the face ahead of the eye and wraps the bill base. It makes the bill look longer and the head look more domed than they really are. Loose shaggy feathering hangs around the top of the legs. A juvenile is duller, with a greenish gloss and brownish-black underparts. Young birds still carry face feathers and lose them at about six months old. Males average slightly larger than females, and the sexes look alike.

Habitat and range

The rook lives across the Palearctic, from Ireland and Scandinavia east to Siberia. Southern limits reach Turkey and Iran, and northern birds stay mostly below 60 degrees. It chooses arable land, pasture, river plains and steppe with soft, fertile soil. Tall trees for nesting must stand within reach of the feeding ground. The bird avoids closed forest, swamp, heath and moorland.

Most rookeries sit below 120 metres, though birds breed at 300 m and higher where food allows. Rooks settle beside farms and villages, and in open towns, though not in heavy city centres. Northern birds drift south in autumn to escape the hardest weather. Southern populations mostly stay put and wander only in a loose way. Several hundred rooks were released in New Zealand between 1862 and 1874. Councils there now treat the bird as an invasive pest and control it.

Diet and feeding

Stomach studies show that about 60% of the food is plant material. Grain, potatoes, roots, acorns, berries, fruit and seeds make up that share. The animal share is mostly earthworms and insect larvae. Beetles, spiders, millipedes, slugs and snails are taken too. The bird also eats small mammals, small birds, eggs, nestlings and carrion.

Feeding happens on the ground, with the bird striding about and probing with its strong bill. The long tapered bill reaches worms and grubs below the surface. Rooks prefer fields of spring barley to tall winter cereals, because short crops are easier to work. In towns they take scraps from bins and streets, usually at dawn or dusk when it is quiet. Like other crows, the rook hides food and returns to it later. Birds in a French theme park were even trained to collect litter.

Behaviour and social life

The rook is one of the most social crows and is nearly always in a flock. Pairs bond for life and stay together inside the flock. Birds gather at the rookery in the evening, then move on to a communal roost. Flocks swell in autumn as separate groups join up, often with jackdaws. In the morning the roost empties, and birds scatter up to 10 kilometres to feed.

Autumn flocks perform group flights with synchronised turns, dives, tumbles and rolls. Flight is direct, with steady beats and little gliding when the bird has somewhere to be. Near the rookery the same bird glides and wheels for longer. Partners back each other up in disputes with other rooks. After a quarrel a bird returns to its mate, and the two twine their bills together. Large colonies change the soil beneath them, which grows rich in droppings and nest waste.

Communication and senses

The usual call is a flat caw, less harsh than the call of a carrion crow. The pitch varies, and the bird has several versions for different situations. A perched rook fans its tail and bows with each caw. Calls in flight come singly, while a crow tends to call in threes and fours. Around the colony the birds add squawks, burring notes and half-chirrups.

A lone bird sometimes sings quietly to itself in clicks, wheezes and near-human notes. Pairs sing duets, which appears to strengthen the bond between them. A female uses a begging call towards her mate. Hearing is sharp, and a rook knows the voice of its partner and of its own chicks. Snarling and gull-like calls warn an intruder away from a nest.

Reproduction and life cycle

Rooks usually take a mate at two years old and keep the same partner for years. The male bows to the female with drooping wings, cawing and fanning his tail. She may crouch, arch her back and quiver her wings in answer. The male then feeds her, and mating follows on the nest. Neighbouring males often mob a mating pair, and the female leaves the nest to end it.

Nesting is always colonial, high in big trees and often on the frame of last year's nest. The male gathers most of the sticks and the female builds them into a cup. Earth binds the structure, and grass, moss, roots, leaves and straw line it. Many sticks are stolen from neighbours rather than broken from a tree. Building can start as early as January in Britain.

A clutch holds three to five eggs, sometimes six and rarely seven. Eggs are laid by late March or early April in Britain and Ireland, and in May farther east. They average 40 by 28.3 millimetres and are heavily blotched in grey and brown. The female incubates almost alone for 16 to 18 days while the male feeds her. He carries food to the nest in a throat pouch, and she joins the work after ten days. Chicks fledge on about the 32nd day, and a wild rook may live 15 to 20 years.

Predators and threats

Owls, hawks and other crows take eggs and young from the nests. Birds of prey attack fledglings far more often than they attack adults. A colony high in the treetops is probably a defence in itself. Rooks mob an intruder and call it away from the nests.

People remain the largest threat, through shooting and the loss of nesting trees. Changes in farming, seed dressings and pesticides all cut the food supply. A moderate decline has been measured in the United Kingdom since 1995. Rooks carry mites in their feathers and single-celled parasites in their blood. Those passengers appear to do the bird little harm.

Population and conservation

The IUCN lists the rook as Least Concern. The range is very wide and the total population is large. Roughly a million pairs nest across the United Kingdom every year. Numbers may be slipping slowly across the range, but not fast enough to raise concern. The bird is scarce in mountains and absent from the centre of large cities.

New Zealand runs the only large control programme against the species. Culling there has destroyed the big colonies, and the survivors have grown wary. Elsewhere the main need is probably to keep tall nesting trees near open ground. Warmer springs may shift the nesting date, and researchers now watch for that. A farm that leaves permanent pasture probably helps the rook more than any protection law.

Relationship with humans

Farmers have long seen rooks in their fields and judged them thieves. Henry VIII brought in a Vermin Act in 1532 that named crows, jackdaws and rooks. Elizabeth I passed a firmer grain protection act in 1566, and large culls followed. Francis Willughby wrote in 1678 that children were sent out with rattles to scare the birds. He also described scarecrows dressed as country workers to keep them off the grain.

Later naturalists worked out that rooks eat more pests than grain. One study found that 60 to 90% of the insects they take are agricultural pests. Their probing also turns and aerates farm soil. Rook shoots were once a social event, and young birds called branchers were shot before they could fly. Rabbit and rook pie was the dish that followed, because an adult rook is not worth eating.

In culture and myth

English tradition appears to give the rook the finest collective nouns of any bird. A group may be called a building, a parliament, a clamour or a storytelling. The word rookery passed from the birds to any crowded settlement. The name itself began as an attempt to write down the bird's call.

In Russian tradition the returning rook announces the end of winter. Alexei Savrasov painted The Rooks Have Returned in 1871 on exactly that theme. The picture is said to be one of the best known landscapes in Russian art.

In British rural tradition the rookery seems to have been a fixture of the village skyline. The nests may sit on a church spire or in the tallest elms, and the noise marks the season. In heraldry the rook is seldom told apart from the crow or the raven. That blurring probably explains why so little rook-specific folklore survives.