The distribution and number of colonies of rooks Corvus frugilegus L. was studied over a three-year period in a landscape in eastern England dominated by winter cereals. Individual rookeries were generally small and not evenly distributed, with a total of 1561– 1637 nests in a 325 km2 study area over the three years. The distribution of groups of rookeries (main colony with satellites) was associated with the amount of grassland, a colony of 100 nests requiring some 122 ha of grass within 1 km. Feeding habitat and preferences of rooks were studied throughout one year. The most consistently used feeding habitat was grassland and it was strongly preferred, with a peak in June. Winter cereals were used from October to March, but were never preferred, other crops being used seasonally. Flock size peaked in February and was smallest during the breeding season, when the mean distance of feeding flocks from the colony was less than 1 km. Increases in land given over to horses, riding and turf production could benefit rooks in the study area.
The rook (Corvus frugilegus) is widely distributed in the Western Palaearctic and is generally regarded as a pest species of agriculture and at airfields. In this study we describe a schematic eye model for the rook. Digital photographs of the intact enucleated eye gave the gross dimensions. The lens and the cornea of the rook’s schematic eye were found to have an almost equal refractive power of Fl 59.53 D and Fc 62.63 D. The rook’s schematic eye has an axial length of 14.50mm and a total power of F 108.86 D. The eye shape is similar to the ‘flat’ eye type. The calculated f-number² value of 3.63 indicates that the rook’s eye is well adapted to high light levels and is not suitable for night vision.