Fauna Gunner

You gain the ability to use small animals, insects and small monsters as ammo, using your crossbow, each creature will required to be tamed or knocked out. they do bonus damage when shot at enemies, but reduces damage from using non-living ammo. requires Special crossbow.

Having this feat allows construction of a Nature Crossbow. and you can use charisma to pacify animals.

You can hold as many creatures as your encumbrance allows, if no encumbrance then free to carry as many as you need.

(No the animals will not eat each-other.)

Though I didn't put it down, anything small or tiny will work.