[linda m clark]

My parakeet's behavior has changed dramatically in the past month from chirping and singing to just sitting on the perch with his head tucked under his wing and sleeping all day. His appetite is good and he drinks water. There are no physical signs of illness, but he's stopped interacting with his cage buddy (an English budgie). He just sits and sleep.
Does anyone know of any syndrome or illness that would cause this behavior? I think it's some kind of vitamin deficiency, but I'm reluctant to take him to the vet until I know more. Bird vets in Calif. are VERY expensive!!