The rook is similar in size to the crow. It has black feathers, which show a blue or bluish-purple sheen (glint) in bright sunlight. The feathers on the head, neck and shoulders are dense and silky. The legs and feet are generally black, and the bill (beak) is grey-black.
Rooks differs from the crow by the bare grey-white skin around the base of the adult's bill, in front of the eyes. The feathering around the legs look shaggier and laxer than the Carrion Crow. The young bird looks just like a crow because it lacks the bare patch at the base of the bill.
Its food is mostly earthworms and insect larvae, which the bird finds by probing the ground with its strong bill. It also eats cultivated cereal grain, smaller amounts of fruit, small mammals, acorns, small birds, their eggs and young and carrion.
Rooks always nest together, usually in the very tops of the trees. Branches and twigs are broken off trees for the nests. There may be any number of nests together in a group of trees: twenty or thirty are often seen in the rookery. This is why rooks are sometimes described as colonial birds.