Common swifts are wholly dependent on aerial insects and spiders for food. Climate change is disrupting insect emergence timing and abundance, creating mismatches between swift arrival from Africa and prey availability in UK and European breeding grounds.
Swift chicks that cannot receive adequate food from parents in cold, insect-poor summers enter torpor — a survival state where they lower body temperature to reduce energy requirements. Prolonged torpor can cause development delays and reduced fledging success. Adults forced to travel further for food face increased energy expenditure. In extreme cold wet summers, entire colonies may produce no fledged chicks. The welfare impact of climate-driven prey mismatch is increasing in frequency and severity.