Magnets interfere with pigeon homing.

Magnets glued to the backs of experienced pigeons often resulted in disorientation when the birds were released from distances of 17-31 miles (27-50 km) under total overcast, whereas no such disorientation occurred during similar releases under clear skies. The magnets did, however, often cause disorientation when first-flight birds were released under sun, and there was some indication of disturbance to experienced pigeons released under sun at longer distances.