 Rockduff, the rockduff, is a member of the bird family Columbia doves and pigeons. In common usage, this bird is often simply referred to as the pigeon. From this species the domestic pigeon descended. Escaped domestic pigeons have raised the populations of feral pigeons around the world. Feral rockduffs are pale gray with two black bars on each wing, while domestic and feral pigeons are variable in color and pattern. Few differences are seen between males and females. The species is generally monogamous, with two squads young per brood. Both parents care for the young for a time. The habitats include various open and semi-open environments. Cliffs and rock ledges are used for roosting and breathing in the wild. Originally found wild in Europe, North Africa, and Western Asia, pigeons have become established in cities around the world. The species is abundant, with an estimated population of 17 to 28 million feral and wild birds in Europe.