Common swifts have declined severely in the UK due to loss of nest sites in modern buildings, with urban conservation interventions showing promising results.
Swift welfare in the UK is primarily threatened by the loss of nest sites as older housing stock is renovated and modern buildings lack accessible eaves. Swifts that cannot find nest sites experience breeding failure and reduced reproductive success. Conservation interventions including swift bricks integrated into new buildings and swift nest boxes installed on existing buildings have successfully created new breeding colonies. Aerial insect abundance affects both breeding success and migration survival. Light pollution can disrupt navigation and cause building collisions. Building regulations requiring swift bricks in new developments in areas with known swift populations represent a structural welfare improvement.