You should be able to tell whether the bugs are actually present, if you check out the link, and check the birds, probably after dark, with a flashlight and a friend. Also check the underside of the roost during the day; one type hides there, then gets on the bird at noght. I would use the Sevin 5% on chicks, myself, if I were quite sure the bug were there, because an infestation of the wrong kinds can suck so much bloood they get sick or even die if extreme. What I have actually done the last few years is dust the nests, areas under the roosts and the dusting areas every few weeks. I've never actually seen bugs or dusted birds -- but these bugs are everywhere, wild bird have them, and I don't believe for a minute that just becaue I couldn't find them meant there were absolutely none present.
There is supposed to be a 3 week withdrawal period for eggs after using Sevin. I've never bothered, and know of several other "old timers" who don't. I wouldn't sell egg for eating for 3 weeks after using Sevin, though -- just in case, just to be safe. You never know who is allergic to what, for one thing. Just my opinion -- you'll have to do things your own way, of course.
Good luck!