Wild birds suffer from a range of infectious diseases, some of which are worsened by human activities including supplementary feeding, window collisions that suppress immunity, and habitat degradation.
Wild birds dying from infectious disease suffer prolonged welfare harms. Trichomonosis causes throat lesions that prevent swallowing — birds starve slowly while attempting to feed. Avian pox growths around eyes cause blindness and impair foraging. Salmonellosis causes weakness, diarrhea, and eventual death over days. Many of these deaths are directly caused by human provision of feeding and bathing resources that concentrate birds and amplify transmission. The welfare case for rigorous feeder and bath hygiene is direct — it prevents suffering we are causing.