Rooks, these very common and very social members of the crow family, are busy building in traditional rookeries. During one of the mildest winters on record, some enthusiastic birds in my neck of the woods were repairing nests in early February. Many are now busily building or are well underway with that stage of their reproductive cycle.
With no leaves on the deciduous trees yet, the nests are very easy to spot. Always at the tops of tall trees, they are often very close to each other. Both parents are involved in building with the male doing most of the work delivering sticks and nest materials and the female focusing on assembling them into a bulky cup.
Of necessity, the stick structure has many large gaps in it early on. These are plugged with earth, grass, roots, leaves and any plant material readily available. When the structure is well formed, it is lined with moss, sheep's wool, hair and other soft materials to make a cosy cup ready to receive the eggs.
Breeding is usually in full swing during March in the south of the country but in the far north weather conditions can delay it to April or even into early May.
When the nest is ready, the parents mate and the female lays one egg per day. A clutch of three to five eggs is normal but clutches of up to nine eggs have been recorded. Rook eggs are smooth and glossy and exhibit great variation in blue and green background colours.
The ground colour is marked with a bewildering array of blotches, spots, speckles, streaks, scrawls and mottling in an equally bewildering array of colours ranging from pale buff to olive to greens that are so dark they are almost black.
The huge variation in both ground colour and markings can occur in one clutch with one egg being pale and sparsely marked while its neighbour is exceptionally dark and heavily obscured with intense markings.
Incubation of the eggs is strictly by the female. While she sits for 16-20 days her male partner feeds her. All going well the young hatch. The nestlings are poorly covered with a scant coat of short down.
The male continues to feed his partner and starts feeding the chicks as well. The female continues to brood them but when they get hardy, she joins the male in feeding duties for 30 days until they fledge and become independent.