Common swifts are aerial specialists that nest exclusively in buildings and have declined 60% in the UK due to loss of nesting access in modernised buildings.
Swifts returning from Africa after a 6,000-mile migration to find their nest site blocked face a critical welfare harm: they have expended enormous energy on migration to no reproductive purpose. Swifts cannot easily locate alternative sites, and adults returning to sealed buildings may attempt entry repeatedly, injuring themselves. Nest site loss also affects the welfare of established pairs by breaking long-term breeding bonds.