Rook bird is an all black corvid with a purple metallic sheen to its plumage. The main difference from its close relatives is its grey bill, with greyish-white skin extending around the bill base and up to the eye, and the lack of the nostril feathering so prominent on both the Carrion Crow and Raven. As a consequence the bill appears more pointed and dagger-like. The head of rook bird is more domed with a peaked crown, and when walking the bird often appears fuller bellied. Juveniles are very similar to Carrion Crow juveniles, lacking the whitish face of an adult Rook and having black feathering over the nostrils until their first spring.
Rook bird is a common, widespread and resident across the region, with birds in northern parts of the range moving south- and westwards in winter. Rook bird is essentially a lowland bird, it favours agricultural areas and can be found in flocks feeding in pastures and on ploughed fields. Areas with tall trees are required for its nesting colonies (rookeries), which are most commonly located in isolated stands of trees and copses in farmland and in adjacent villages.
Calls include a simple "caw", similar to that of the Carrion Crow but less rolling and more grinding in quality, a harsher, hoarse and nasal "graaah" or "geeeah", and a multi-syllable "gra'gra' grrahh". This call of rook bird is lower in pitch than the Carrion Crow's and delivered in an even flat tone; however, the call can be varied somewhat and there is also a higher-pitched 'hiccup' sound, such as "khuow". Females also give a longer, higher-pitched call, "kraaa-a". As so often in flocks, the calls sound repeated and even overlapping, and when at a rookery can provide a near-deafening cacophony of sound at close range. The male gives a 'song' in courtship, a medley of various call notes and said to resemble the Starling's song.