The most urban of the swallows. It nests under the eaves of buildings, often in colonies, building mud nests in the form of a closed cup with a small entrance hole. It has very dark back, wings and tail, with some bluish iridescence on the back, with a white rump and underparts. It feeds on insects generally taken on high altitude flight. It returns from Africa each spring to breed in Extremadura and leaves again in September.