Yes you are all correct. I have seen these before and they are, indeed, tapeworm. Unfortunately there are very few treatments out there approved to treat them. There are also many misconceptions about Diatomaceous Earth. It only treats fleas, lice, and roundworm. It does not penetrate the larvae of some of the more serious types of parasites--while it is very beneficial for holding off a plethera of blood-sucking, aggrivating ones.
I use Fenbendazole, though I do not believe even this will treat tapeworm. Your very best bet would be to take Peter's recommendation at Tri-State. I would trust my flock to that man any day. He is a Godsend when dealing with this type of problem.
I would recommend treating your soil with Agricultural lime--especially if you have horses. Horses carry this parasite and rodents are the worse culprits for the spread of this parasite TO BIRDS. The most prevelant spreader of this type of tapeworm is your conventional, everyday flea.