Barn swallows are declining across much of Europe due to insect prey reduction from agricultural intensification, directly impacting individual bird welfare and breeding success.
Individual barn swallows experiencing insufficient prey availability during the breeding season face energy deficits that affect their ability to provision chicks adequately. Chicks in years or locations with low insect availability receive insufficient food, causing starvation and failure to fledge. Adults undertaking extended foraging trips in poor conditions are subject to increased energy expenditure and physiological stress. Loss of accessible farm buildings removes nest sites, forcing birds into suboptimal locations with lower breeding success. Insecticide use on farmland, both reducing target pest insects and non-target invertebrates, is a primary driver of prey availability reduction that directly causes welfare harm through nutritional stress.