It is mainly caused by diseases, especially Bumble-foot or pigeon pox. Bumble-foot deformities on pigeons' feet are caused by infection with Staphylococcus aureus bacteria, which are present on the skin (just the same as on our own) and in the pigeons' droppings, get into the foot through cracks and cuts in the skin and eventually cause tendonitis, arthritis and joint abscesses. Other causes are wire and synthetic thread injuries.