Migrating birds face an gauntlet of human-created hazards including buildings, power lines, communication towers, and light pollution that kill hundreds of millions annually.
Migrating bird welfare at the landscape scale is shaped by the accumulation of individual infrastructure hazards across thousands of kilometres of migration route. A warbler that survives the Sahara crossing may be killed on a building in London or Frankfurt. The solutions are technically straightforward - window film, flashing rather than steady warning lights, power line design changes - but require regulatory mandate or voluntary adoption by building owners and utilities. The welfare argument for individual birds is amplified by the conservation argument for declining migratory species: populations of swallows, warblers, and flycatchers that have declined by 30-50% cannot absorb infrastructure mortality without population consequence. Individual and institutional action on migration hazards contributes to welfare at the population level.