Common swifts spend most of their lives in the air and face significant threats from loss of nesting sites in modern buildings.
Loss of nesting sites forces swifts to either fail to breed or search for increasingly scarce alternatives, with energetic consequences for adult birds that have evolved to nest without searching. Failed breeders that cannot find nest sites carry full reproductive investment with no outcome, representing a significant welfare cost at the individual level. Young swifts that cannot locate nest sites leave for Africa without breeding for two to four years, during which they depend entirely on aerial habitat quality. Simple provision of nest boxes provides immediate relief, and swift bricks embedded in new buildings offer permanent habitat restoration.