Just check the bases of their feathers on their necks, on their backs, and espeically on their belly/cushin fluff under their tails. I find feather lice to be a bigger issue up here since more than one bird I have gotten has had it. Luckily I kept them in their own area and dusted them clean before going with the rest of my flock. To control it, just make sure your stock doesn't have it, quarentine new birds at least a month and do inspect them, and avoid atracting wild birds near your flock. If you get it, just get some poultry dust from the feed store and after a month or two of dusting on schedual, you should be able to rid of it. You can also look for egg clusters at the little bits of fluff at the base of feathers.