If it looks like a chicken, walks like a chicken, and sounds like a chicken, then why go through the bother of coming up with an 'exotic' sounding name. Call it a chicken. Save your creative names for the six-legged turtles.
As for killing them, should you be able to kill them? Realistically, yes. But consider the other side of reality. What kind of disturbed moron goes around killing chickens randomly? Well, that would be the kind of morons more than half of the people playing the game would become at the first sight of the bird. Game mentality: If it moves, kill it. Reason IC? No good one. it is the same reason you can't kill Harn, or he would have been dead the first day.