Firstly you need the Huntress Outfit, you get it as a Reward for completing the Mission A Hearty Meal, then equip Outfit in a Basecamp. A good place to kill 50 animals is here in the Geothermal Valley, since the chickens and birds respawn almost immediately.
other Rise of the Tomb Raider Achievement Guides
|No Stone Unturned||Achieve 100% game completion|
|Quite TIme||Find the best seat in the house|