If they are white to beige colored they are lice. Diatomaceous Earth, food grade, is a great way to keep lice down on a regular basis. Once they are on your birds you need to treat the bird. Follow the directions for whatever de-louser you are using. Or go the the thread about lice under the emergency/illness tab. There are dozens of things you can use for lice, some more toxic than others. Treatment needs to done quickly as they can drain a bird of blood fairly rapidly. I washed my birds with Adams flea tick for kittens (a light dose) and rinsed them, and kept them inside at night and then got rid of all the bedding in the coop. You can read about bird bathing techniques under the same section as above.
