Crag Martin (P. rupestris) breeding in southern Europe are largely resident, but some northern breeders are migratory, wintering in north Africa or India. They do not normally form large breeding colonies, but are more gregarious outside the breeding season. These martins build neat mud nests under cliff overhangs or in crevices in their mountain homes and have readily adapted to the artificial cliffs provided by buildings and motorway bridges. Up to five eggs, white with dark blotches at the wider end, may be laid, and a second clutch is common. These martins are 12–15 cm (4.7–5.9 in) long with drab brown or grey plumage and a short square tail that has small white patches near the tips of all but the central and outermost pairs of feathers. The eyes are brown, the small bill is mainly black, with the legs being brownish-pink. The sexes are similar, but juveniles show pale edges to the upperparts and flight feathers.