My 3 year old rooster, Onyx, has been acting sick the past few days. He stands like a hen with egg peritonitis, and his stool is a yellow-green color. He is able to walk and run, just in an awkward, struggling way. After a little activity, he stands in that position again and looks like he's trying to lay an egg, or he will sit down. He eats very well still and drinks well. What could be wrong?