Rook

On an adult, look at the face and bill. A rook has a long, slender, pale-grey bill with a patch of bare, pale skin around its base, giving a peaked-forehead, Roman-nosed profile, while a carrion crow has a shorter, heavier, all-black bill and a fully feathered black face with a flatter forehead. A perched rook also shows loose, shaggy feathering on the thighs, like baggy trousers, which a crow lacks, and its plumage has a purple sheen against the crow's greener gloss. Behaviour is the strongest clue of all, since rooks are highly social and are almost always seen in flocks and colonies, whereas carrion crows are usually seen singly or in twos. A young rook with a feathered face is genuinely difficult and often has to be judged by the company it keeps.

A rookery is a breeding colony of rooks, a cluster of large stick nests built close together in the tops of tall trees, often the same stand of trees year after year for decades or even centuries. A rookery can hold anything from a handful of nests to several hundred, and in spring it is a scene of constant activity and noise, with birds carrying sticks, defending nests, and calling. Rooks return to the rookery to refurbish nests well before laying, and pairs whose nests are on the edge of the colony sometimes have sticks stolen by neighbours nearer the centre. The word rookery is now also used loosely for the dense breeding colonies of other animals, such as seals and penguins.

The relationship is mixed. Rooks do take newly sown and ripening grain, and a large flock can damage a field of germinating cereals or maize, and they will pull at seedlings and take some fruit, so historically they were shot and their rookeries destroyed. On the other side, rooks eat very large numbers of soil pests, particularly leatherjackets and wireworms that damage grass and cereal roots, so across a whole farm year the balance of benefit and harm is not clear-cut. Modern practice leans toward scaring rooks off vulnerable crops at key times rather than trying to reduce their numbers, and rookeries themselves have some legal protection in parts of the range.

Very. Rooks belong to the crow family, which rivals the great apes for problem-solving, and in captivity rooks have performed impressively on cognitive tests, spontaneously bending a straight wire into a hook to retrieve food, using stones to collapse a platform or to raise a water level and float a reward within reach, and cooperating with a partner to pull a baited tray. Interestingly, wild rooks have almost never been seen using tools, which suggests they have the general intelligence to invent tool use when a situation demands it but rarely meet such a situation in their normal life of probing soft farmland soil. Their tight, lifelong pair bonds and complex colony life also point to sophisticated social cognition.