Yes, we're finishing "Bird Week" with two for the price of one. House Martins are attending nests in Albion Street, and Sand Martins can be seen hunting insects above the Wharfe upstream from Wharfebank Mills.
House Martins are distinguishable from Swallows by their white rump and preference for urban settings, where they often nest under eaves. They also typically feed at higher altitudes than Swallows and so don't compete. Young from a first brood will sometimes help feed the second, an unusual occurrence in the bird world.
Sand Martins are a similar shape, but brown instead of black, and lacking the white rump. Similarly sociable, they nest in colonies in sandy riverbanks and cliffs, digging burrows up to a metre in length. There used to be such a colony on the Wharfe just downstream from Gallows Hill.