Common swifts are declining across Europe as old buildings with nesting holes are renovated, closing traditional nest sites that swifts return to for decades.
Swifts denied access to traditional nest sites by building renovation face reproductive failure as they are highly site-faithful and reluctant to use new sites. Birds that cannot find nest sites waste critical breeding season energy in aerial prospecting. Swifts injured and unable to fly are helpless on the ground, as their foot morphology prevents terrestrial locomotion. Declining insect populations reduce food availability, causing chick starvation in poor weather years.