head and wings and erecting her partially spread tail over her back. Further similar displays are often followed by begging behaviour by the female and by the male presenting her with food, before coition takes place on the nest. At this stage, nearby male rooks often mob or attack the mating pair, and in the ensuing struggle, any male that finds himself on top of the female will attempt to copulate with her. She terminates these unwanted advances by exiting the nest and perching nearby. A mated pair of rooks will often fondle each other's bills, and this behaviour is also sometimes seen in autumn. Breeding Nesting in a rookery is always colonial, usually in the very tops of large trees, often on the remnants of the previous year's nest. In hilly regions, rooks may nest in smaller trees or bushes, and exceptionally on chimneys or church spires. Both sexes participate in nest-building, with the male finding most of the materials and the female putting them in place. The nest is cup-shaped and composed of sticks, consolidated with earth and lined with grasses, moss, roots, dead leaves and straw. Small branches and twigs are broken off trees, though as many are likely to be stolen from nearby nests as are collected direct, and the lining material is also often taken from other nests. Eggs are usually three to five in number (sometimes six and occasionally seven) and may be laid by the end of March or early April in Britain, but in the harsher conditions of eastern Europe and Russia, it may be early May before the clutch is completed. The background colour is bluish-green to greyish-green but this is almost completely obscured by the heavy blotching of ashy grey and brown. The eggs average in size. They are incubated for 16–18 days, almost entirely by the female who is fed by the male. After hatching, the male brings food to the nest while the female broods the young. After ten days, she joins the male in bringing food, which is carried in a throat pouch. The young are fledged by the 32nd or 33rd day but continue to be fed by the parents for some time thereafter. There is normally a single clutch each year, but there are records of birds attempting to breed in the autumn. In autumn, the young birds of the summer collect into large flocks