Generally speaking, when a substance hangs around for the long term in a body, it's trapped inside of a particular type of tissue and is non-bioavailable. That's why critters who are treated effectively with a medicine can fall prey to the same illness again. While Tylan specifically isn't used in humans it's close relative erythromycin is. Terramycin is just tetracycline. Most of these drugs are safe for human consumption. The rub is in the fear of overmedicating the populace and creating drug resistance, as well as the problems associated with killing off the body's natural flora. Even wormers like Ivermectin are used on humans. Controlling the amount of exposure you have is wise. If you follow the withdrawal times associated with the drug, even if it's only listed for milk or meat, you should be fine. If you have an allergy to a related drug, you may want to wait longer. I certainly wouldn't fear contamination for the lifetime of the bird.