One possible cause is trauma or injury, such as a fracture or nerve damage. Infections, such as viral or bacterial infections, can also affect a bird's nervous system and cause paralysis.
Additionally, certain diseases, such as avian botulism or West Nile virus, can affect a bird's nervous system and lead to paralysis. Poisoning, either from ingesting toxic substances or from exposure to environmental contaminants, can also cause paralysis in birds.