Yes happy chickens indeed, as for their hearty constitution. I believe that most living creatures are extremely adaptable in regards to our enviroment. Humans even more so than animals although it would seem that we are the most prone to our minds getting in the way. While animals are not inhibited by complex thought or even an overly complex fear of death even. They just naturally adapt as long as their enviroment is survivable, even as far as to evolve their physical features. If i remember correctly, chickens come from a jungle climate originally .