Barn swallows have declined by 46% in the UK since 1970, with reduction in insect prey, loss of nesting sites, and weather during migration all affecting welfare.
Barn swallows dependent on insect-poor farmland face chronic nutritional stress during the breeding season. Parents making hundreds of foraging flights daily to provision chicks face physiological exhaustion when prey density falls. Chicks that hatch in insect-poor periods may not receive sufficient food for full development, leading to poor condition at fledging and reduced migration survival. Nest site loss adds displacement stress to nutritional challenges.