It is important that pet bird owners be able to differentiate between regurgitation and vomiting in birds.
Regurgitation is a normal part of breeding behavior that is to be expected in healthy birds. If your single pet bird views you as its "mate," then it may bestow upon you the highest honor of regurgitating on you to show its affection toward you. A bird that is regurgitating will bob its head and stretch its neck. Regurgitated food is often still somewhat intact (it hasn't yet been entirely digested).
A bird that is vomiting will often spew partially digested crop contents (food) in a haphazard manner. The owner may find the vomit encrusted on the bird's head and/or feathers. Actual vomiting in birds is not common; however, if your bird is vomiting and begins to show other outward signs of distress, consult an avian veterinarian as soon as possible. Gastrointestinal (GI) disorders, motion sickness (riding in cars), poisoning and anesthesia may cause vomiting.