I can now testify first-hand that there is indeed a Westfall chicken quest. I'd always kind of suspected it was a rumor. However, yesterday, a couple level 40s were /chicken-ing the chickens while I was turning in The Killing Fields, and one of the chickens turned green. I managed to catch the quest before it went away. (The chicken didn't stay green long.)

Now, my non-demonologist warlock has a Prairie Chicken vanity pet. I've won WoW. (Don't worry, I'll keep playing. If I stopped playing, I wouldn't get to enjoy the Prairie Chicken.)