|Picture © Bokkaku on Deviantart|
Regurgitation is a normal part of budgie behavior that shows that your bird is healthy. A budgie that is regurgitating will bob its head and stretch its neck. Regurgitated food is still somewhat intact (it hasn't been entirely digested yet).
Regurgitation may also be a sign of a crop infection, but many happy budgies regurgitate to their favorite toy or person and this is not a sign of any infection. It's their way of showing that they love you!
Important: don't confuse regurgitation with vomiting!
A budgie that is vomiting will spew partially digested food (or other crop contests) at random moments, without having this under control. The food remains often stick to the budgie's head and feathers. Vomiting is not very common among budgies; however, it should always be taken seriously, especially when your budgie vomits more than once. Then you should consult an avian veterinarian as soon as possible. Gastrointestinal disorders, motion sickness (riding in cars), poisoning and anesthesia may cause vomiting.
On a sidenote: Isla vomited several times when she was suffering from a parasite infection. It's often a clear signal that something is wrong. I was told that budgies may also vomit when they're in a stressful situation (for example: when there are conflicts with other budgies in the cage).