It's really more a case of the *mascots* being mammals, isn't it? I mean a Buffalo Bill isn't a (non-human) mammal, and a predator isn't inherently mammalian.
The buffalo bills shouldn't appear because they're named after a human. If they're in because of the word "buffalo" you should rename the quiz to "teams with mammals in their name. The Denver Broncos should be accepted since Bronco definitely refers to a mammal, even though not a specific breed, and I'd have the Predators in grey as a given answer because the term can refer to non-mammals as well as mammals.
yeah, I forgot the broncos. I also did it based on the logo/mascots more than the actual thing it's named after (although I didn't include the sabres). I included the predators because their logo is a saber toothed tiger (I think)