Could it be ticks? They look like engorged ticks to me. But I don't know. Sure is an infestation though. I have never seen chickens with them like that!
Take a look at the photos in the link, post #6: Use a magnifying glass and compare them with the photos to identify which parasite you're dealing with.
Sevin dust will take care of the lice and mites. Ivermectin will take care of mites, sticktight fleas and fowl ticks.