Cysts
Feather cysts are common in budgerigars and although they can appear anywhere, they are more commonly associated with the primary feathers on the wings.
They occur when a growing feather is unable to grow through its natural opening in the skin and curls up within the feather follicle. Feather cysts appear visibly as oval or elongated swellings involving one or more follicles.
The cyst can become very large and may rupture, which can cause pain and blood loss for the bird.