The rook (Corvus frugilegus) is a member of the family Corvidae in the passerine order of birds. Its range spans from Scandinavia and western Europe to eastern Siberia. Rooks are large, gregarious, black-feathered birds with a distinct whitish featherless area on the face, nesting collectively in rookeries. They are mainly resident birds but northern populations may migrate southwards to avoid harsh winter conditions. Rooks form flocks in winter and return to their rookeries for breeding in spring. They forage on arable land and pasture, feeding on grubs, soil-based invertebrates, and plant material. The rook was named by Carl Linnaeus in 1758 and has two recognized subspecies. With a wingspan of 81 to 99 cm, rooks are commonly found in open agricultural areas with suitable tall trees for breeding. They are associated with human settlements and are highly gregarious, often seen in flocks. Rooks are intelligent birds with complex behavioral traits and an ability to solve simple problems. Rooks are also known to have been introduced into New Zealand and are regarded as an invasive pest.