Ive had my chickens for about 6 weeks now, 3 hens and a cockerel, I'm new to keeping chickens but yesterday I noticed that the cockerel was being a bit sluggish and looked depressed. He had no physical injuries and all his obs seemed fine. Then this morning when I let them out of the coop, they all ran out apart from the cockerel who continued to perch up on his roost. This is when I really noticed something was wrong, they are always desperate to get out and find some morning worms. He just looked grumpy, anyway I left and was going to separate him from the hens when I got home from school but when I got home he was lay on the floor of the coop, dead. I was so so shocked!! Awful experience but does anyone know what could have happened?! And what should I do with the rest of the hens?! Are they ok or do I need to treat them for something? Thanks in advance, any help is hugely appreciated!