Each of the Slam Cup achievements are in theory unlocked once you’ve killed each of the different species, and types of the specified animals you encounter throughout the game. All with the exception of the upland bird you will get during the normal play of the game, because each animal is hunted during the course of the game. One of the upland birds however appears in only two of the later missions as a special animal to hunt. This is done in the first arcade mission after finishing the south region. The upland bird is hiding in the bush directly in front of you. This is the challenge in which all the foxes are running through the woods and you have to pick them off. Once they run by the bush they’ll scare the bird out, just shoot it for the achievement.