Ok so maybe that is parts of scratch like I originally thought. I don’t add ash to my run. Idk if you can tell that well from pics but pics I took over the weekend show color of dirt in their run where they are now confined to(well that and inside their coop and stuff) since like Oct cause they have no cover. Hawks are big issue here. I just never have seen their poop this dark not even when they had full access to blueberry plants and stuff. Nothing has changed though but suddenly their droppings are this color! And smaller darker color in last photos i posted.The only worms where you would see segments in the poop would be Tapeworm proglottids. You would see them moving like in the video below.
Are your birds molting? Could it be keratin sheaths you see?
Dark poop can be from a number of things. Do you add ash to your run, what's the color of your dirt?