Do they live in those circumstances permanently? If so, that could be a cause of chick mortality right there. Grass has vitamin A in it among other healthy things including of course chlorophyll which detoxes them, and is known to aid in fertility and reproductive success; vitamin A is rather often referred to by vets as the paramount reproductive-aid vitamin. The black of their poops isn't black, which doesn't mean they're not healthy enough, it just means they could be a little healthier. But of course that all depends on diet. They're interesting looking birds. I thought they were just for meat, or do you breed them for meat? Best wishes.