Do you let them free-fly? Do you race the pigeons? If they are out exposed to the elements, this could make a difference if they need deworming. In Ca...is your climate dry? In dry climates, Ivomec given orally every 6 months is recommended. I would have a vet check a fecal sample first before I gave any dewormer though. If they do have worms, the medications need to be rotated to completely break the parasites life cycle.