Common swifts have declined by 60% in the UK since 1995 as building renovations seal traditional nest sites — nest box provision and planning policy changes are the primary welfare and conservation interventions available.
Swifts that return to find renovated nest sites sealed face repeated fruitless site visits before abandoning established colonies — birds that have used sites for decades lose their breeding location. Swifts attempting to enter sealed sites risk injury and exhaustion. Young swifts that fledge from colonies and return the following year to establish nesting locations find no suitable sites in areas where building stock has been renovated without mitigation. Swift welfare at individual level means securing the nest sites that are indispensable to their entire breeding biology. Action at planning policy level has the largest welfare impact per intervention.