Barn swallows depend on flying insects for food. Their population decline reflects the collapse of farmland insect communities caused by agricultural intensification.
Swallow chicks in territories with collapsed insect prey face starvation. Parent birds must travel progressively further to find adequate prey, increasing their own energy expenditure. The insect decline driving this welfare harm is reversible through farming practice change - wildflower margins, reduced pesticides, and diverse crop rotations all support insect recovery that directly benefits swallow welfare.