The Black Redstart evolved to live in holes in cliffs and the like, and never used to be widespread in the UK. After the second world war, cities all over the south were bombed out, and they moved into the deserted, derelict bombed areas in great numbers. As the bomb sites were cleared and the cities redeveloped, their habitat was eroded. But at the same time, Britain was de-industrialising, and they moved into the abandoned factories in the North. As those now get redeveloped, they are losing their habitat again.