Thanksgiving achievement in Shadow of the Tomb Raider

The first step to completing this is acquiring the "Serpent's Glint" skill as a part of Scavenger (green) section. After this, you'll want to craft flare rounds for you pistol.

Next, to find the turkey, you'll want to go to the Mission of San Juan, and travel to the Ruined Tower campsite. Walk around slowly and the turkeys should eventually spawn, but can get spooked if you get near them. Once they spawn, shoot your flare at one and land a direct hit in order for the achievement to unlock.

NOTE: If you are still having trouble getting them to spawn, go to the above mentioned location, completely close the game, then continue your game. This will cause them to spawn every time. Thanks to user "Sighris" for the recommendation.