Has he been checked by a vet? I always ask this question first. Parrots do regurgitate during mating times or to show their "affections" to their humans at times. Usually it doesn't look like what you are describing though (at least none that I have seen). Parrots with asper. will sometimes have a mucus type of discharge that can collect and come out but again not sure if it is exactly like you are describing. Especially if is appetite is not strong or if there is any changes or lessening of feces then a vet is needed. Sorry I couldn't be more help