First of, all the animals must be killed in one game mode (that is, only in single player or multiplayer, you can't kill half of them in single player, and the other half in multiplayer).
- Across all the game map, you can find crows (listen the sounds they make), deers, horses (both wild and domesticated), owls, (only at night), rabbits, raccoons, skunks, snakes, (listen their hissing sounds), songbirds, vultures (only near corpses), and wolfs.
- Near Tall Trees you can find bears, beavers (near rivers), bighorns (also in New Austin and Nuevo Paraiso, near the mountains), boars (also near MacFarlane's Ranch, Stillwater Creek, and Thieves' Landing), bobcats, eagles (also in Nekoti Rock), elks, and foxes (also in Riley's Charge, Rio del Lobo, and Del Lobo Rock areas)
- Hawks and coyotes appear across all Nuevo Paraiso and New Austin.
- Seagulls only appear in Blackwater, near the coast.
- Buffalos only appear in Great Plains, near Blackwater and Beecher's Hope.
- Ducks only appear along the San Luis River and lake Don Julio.
- Armadillos appear in Cholla Springs, Gaptooth Ridge, and Río Bravo.
- Cougars are a bit tricky. They spawn in Rio Bravo, Repentance Rock, along the US/Mexico border, Tanners Reach, Beecher's Hope, and near the Wreck of the Serendipity. Sometimes they hardly appear, and sometimes they spawn in other areas like near Fort Mercer or north of Blackwater.
You don't need to kill bats, dogs nor any animal farms (pigs, bulls, cows, mules, etc).