Migratory Birds
The migratory birds that left our skies did not venture to other countries; they travelled to a parallel universe. Upon their return, they no longer flew in flocks but erratically and chaotically in barmy orbits.
They crashed onto the window panes of houses, drowned by diving in lakes or rivers, and built their nests before mirrors. The worst part was that their songs no longer diffused into space but only vibrated into our heads.