house martin birds, delichon urbicum, building nest cups from mud in gaps on the chalk cliffs, yorkshire

adult animal barn bird birdwatching breed breeding brood build building chalk chick coast common delichon environment feed fledge fledgling flight fly ground group habitat hirundinidae house housemartin martin migratory mud nature nest nestling nurture ornithology outdoors pair sand sitting songbird spring swallow swift urban urbica urbicum wall wild wildlife