Hello!
The behavior is see is delayed emptying of the ingluvium (crop). The birds motion is attempting to move ingesta. I most commonly see ingluvitis caused from Candida albicans, a type of yeast that is ubiquitous in the avian world. Predisposition to this comes from dampened feed that isn't changed daily/contaminated with other chicken stool, etc. etc. The birds immune system is overwhelmed and infection sets in. There are bacterial causes as well but not as common. Generally with this specific condition you can notice a "sour smell"- the laymen's term is "sour crop". It can best be diagnosed through exam, culture/staining of crop contents, and radiographs. Sometimes a simple fecal smear and stain will find the budding yeast in the stool as well- it is important to find the "budding form"- yeast is common components of diet and you cannot default to infection if you see a few non-budding forms.
As far as treatment- you will actually save money by having a specific diagnosis. Then it
can be specifically treated. Doses of all medications are based on weight and there are a number of effective, relatively inexpensive treatments. I would hesitate to place the bird on a "preventative" dosing. this organism, as with most fungal/bacterial and even parasites, can become resistant, thus complicating the case. As stated, we catch all our birds in complete darkness with the red light, or memorize where they are before turning out the lights and simply pick them up.......doesn't work for owls
Kirk