western house martin or delichon urbicum

western house martin delichon urbicum common nest mud pellets eave migratory birds three animals two chicks feeding mature head beak vertical surface overhang breeding convex cup narrow opening fauna swallow darkblue white rump human habitation urban internal parasites external fleas brick wall summer season nature corner bird flight complex movements wings aerodynamic forces upward force movement motion villaviciosa asturias mother flying back eaves