Common swifts are rapidly declining UK breeding birds. Providing nest boxes and preserving nest sites in buildings is one of the most effective individual actions for urban bird welfare.
Swift welfare is closely tied to nest site availability. Birds that return after winter migration to find their nest sites sealed or demolished experience severe stress and reproductive failure. Pairs that cannot breed may attempt repeatedly for a season, expending enormous energy. The cumulative effect of habitat modification across UK urban areas has removed millions of potential nest sites over decades. Individual buildings with swift boxes can host breeding colonies for generations - a highly durable welfare investment for a small upfront cost.