The common swift spends more time airborne than any other bird, sleeping, mating, and feeding entirely on the wing, yet its welfare is critically dependent on the nest holes in old buildings that are being progressively eliminated by renovation.
Swift welfare is primarily threatened by the loss of nest holes through building renovation, modernisation of roof structures, and inappropriate pest control that eliminates nest access. The species site fidelity means nest hole loss is irreversible at the individual level. Young swifts that fledge from a site return to that site three years later, finding it renovated and inaccessible, with severe welfare consequences. Swift boxes installed in new buildings rarely compensate for the volume of natural holes lost through renovation.