What are the signs of mites or lice and how do I treat my birds if they have an infestation?
Mites and lice are a common problem for chickens and can be carried in by wild birds, so if you have an infestation, it doesn't necessarily mean your management practices are bad. However, infestations can cause a reduction in laying, pale combs and wattles, anemia and even death! Infestations can also cause feather loss, usually on the back, because a bird may overpreen and pluck her own feathers in attempt to get relief. It is similar to the loss of feathers caused by too much attention from a rooster, however a rooster normally cause broken feathers, at least at first, whereas mites can cause feather loss down to the skin quickly--sometimes the skin is irritated and red! If you have mites or lice, you will need to treat your birds.
Mites inhabit your birds' feathers and suck their blood: they're like fleas, lice or mosquitos that live in your hair--yuk! Luckily, the types of lice and most mites that affect birds are not interested in humans. A mite is so tiny, it's hard to see, and some types of mites only come out at night. If you have good vision, you may be able to see them around your bird's vent or beneath her wings, especially if your bird has light colored feathers (easier to see the mites against). Lice are larger, but they're lighter colored, too--they're nearly as hard to spot as mites.
There are various treatments for these avian parasites, but they more or less all involve using a pesticide dust or spray on your birds. This sounds sort of terrifying, but think of it like a flea dip for birds. For a non-chemical solution, Diatomaceous Earth can help prevent and treat some types of mites and lice, however it works slowly by mechanical action (sort of scratching the bugs to death). We do recommend using a few handfuls of DE in your birds' dusting areas to help prevent infestations.
If your infestation is severe, you may want to use something that will kill them on contact to provide your birds relief. You can use either a dust or a spray. We prefer the dust treatment because the girls usually enjoy the feeling of dust in their feathers, whereas they dislike getting wet. Be careful when applying the dust, though, that neither you nor your birds breathe it in. We have used old spice shakers (clearly marked POISON). Other people prefer to fill a toe from an old pair of ladies hose with the powder and pat it on that way: the dust is so fine it filters through like a powder puff. When you apply your treatment, pay particular attention to the areas around their vents and beneath their wings. If you have a rooster make absolutely sure to treat him thoroughly, as if he has mites, he will spread it back around to the rest of your girls!
As you are applying the powder, be aware that your birds may decide to react to your kind ministrations by flapping their wings vigorously, making a real dust cloud that you don't want to breathe in, so be sure to hold them firmly.
You can read about treatment options here in this off-site PDF from Kansas State University.
Scaly leg mites can also cause problems for your birds, but they are treated differently. Your birds may have scaly leg mites if the scales on their legs begin to lift up. This is cause by the mite waste building up under the scales; it is painful and eventually debilitating for your birds. You can treat for scaly leg mites by rubbing on petroleum jelly or even an antibiotic ointment that uses petroleum jelly as a base. Some people prefer to use oil, or even something like a Pam cooking spray. You will have to treat every two or three days for several weeks, and the scales may not return to normal.
Some people recommend treating scaly leg mites with things like WD-40, but that's a bad idea. WD-40 has strong fumes that the manufacturers warn can cause respiratory irritation, so it is bad for your birds' lungs and respiratory system. In addition WD-40 carries a caution recommendation that if it comes into contact with your skin, it should be immediately washed off. Purposeful application of this product to your birds is a very bad idea--don't listen to anyone who tells you to treat your birds with this product!