Perhaps this is a side effect of current settings ...
**"Right now, NPC natural creatures will *not* attack players. At present we've set the "FearOfMan" parameter up to a Spinal-Tap-inspired "11" for all natural beasts so that it overrides their "Aggression", "Territorialism" and "Hunger" parameters. They will therefore not act aggressively towards players, and will shy away from nature-initiated contact with player armies or caravans. This will change in the fullness of time (and we will give advance notice before this change). Please be aware that this does not apply to "un-natural" creatures, such as Corrupted units that the Melders might send your way. You, yourself, can still attack animals as usual." - GM SC
I dunno how close you are trying to model the real world. However, critters are where the food is ... even a bigger factor than where the enemy is not.