I decided to take on three Bellowbacks at once last night (it appears I am indeed a Bellowback girl). Used some ruins to protect myself while sniping with freeze balls and normal arrows, then dodging out and stabbing with my spear.
Once all three were dead, I realised that having torched the surrounding countryside, the place was littered with dead animals! Gathered all those up and had enough animal bits to completely enlarge my resource backpack.