You can try teaching them to "go potty" but I am not optimistic. We had parrots, and parrots are WAY smarter than chickens. The parrots were trained to "go poo" if you put them down on the perch and gave the command. But this wasn't really training the parrot, it was training the people. The parrots couldn't hold their excretions voluntarily. Instead, you just knew that they would need to go every 20-30 minutes. So, you saw your 20 minute deadline coming up, you'd put them on the perch, and tell them to go. Then you'd know you had another 20-30 minutes before they'd have to go again.