Wild - I completely agree. If wolfbats ever did go after i bison, i can't imagine them not doing it as a pack due to the size difference. Even then, they may only go after the young, sick, old, etc.
Swamp - their territories may have changed due to the increasing rarity of bison (which i believe to be an outcome of over hunting by humans). If the bison were gone, they may have no more reason to remain there. However, wolfbats were only featured for a brief period, so we know very little about them and there's a lot of room for speculation. Perhaps they do currently, or could have lived near air temples at some point. In any case I imagine they were more widespread in the past, but as human cities expanded out from the lion turtles a lot of the wolfbat population probably suffered from habitat damage, hunting, or loss of prey. This would basically force them into very small areas, such as the cave of two lovers, and make them much less common. I mean, if i were part of an earthkingdom village and there were flying wolves that constantly tried to eat my pigsheep, I'd certainly want to gather some friends and do a bit of "pest control". (not to say that I don't like the idea of wolbats, they and most of the avatar chimeras are pretty cool)