The mere sight of illness may kick-start a canary’s immune system
Simply seeing another bird get sick is enough to trigger an immune response in healthy birds

Canaries (one pictured) can kick-start their immune systems to deal with potential pathogen threats before the birds actually become infected. In a laboratory experiment, being housed near sick birds prompted healthy canaries to mount an immune response.
Juniors Bildarchiv GmbH/Alamy Stock Photo