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The western house martin was originally a cliff and cave nester, and some cliff-nesting colonies still exist, with the nests built below an overhanging rock. It now largely uses human structures such as bridges and houses. Unlike the barn swallow, it uses the outside of inhabited buildings, rather than the inside of barns or stables. The nests are built at the junction of a vertical surface and an overhang, such as on house eaves, so that they may be strengthened by attachment to both planes.
