I see this thread is a couple weeks old, but I wanted to clarify. I am a trained scientist and professional biologist and my training includes the field of animal behavior. Current scientific understanding does not state that chickens, birds, or any vertebrate species operates purely on instinct. This also holds true for some invertebrates. Modern biology states that emotions exist in human and non-human animals because emotions impart a survival advantage. The specifics of emotion lie along a continuum across the animal kingdom. The idea that animals don't experience emotion is outdated and was largely based on religious beliefs (man as separate from all other animals). So the question is not whether they experience emotion but which emotions and to what degree. That is a very active field of inquiry these days, especially now that techniques such as MRI can be employed.