Dogs allowed to run free will often band together to form a pack. Dogs still have the ancient instincts of their wolf ancestors and these instincts are revived when dogs "pack" or are in the presence of "prey." The best family dog can revert to an aggressive predator of wildlife. Dogs in packs will attack livestock, other pets, wildlife, and people. When dogs kill, they seldom go for the throats or do an efficient job. Dogs often attack from the rear, badly mangling their victims as they tear at the hind legs to bring down their prey.
With the exception of using trained or controlled dogs to chase or herd away game animals to protect humans, lawns, gardens, livestock, or agricultural products: " any peace officer, game warden, or other person authorized to enforce the Montana fish and game laws who witnesses a dog chasing, stalking, pursuing, attacking, or killing hooved game animals may destroy that dog, on public land or on private land at the request of the landowner, without criminal or civil liability." (SB 104, 2001 Legislature)
In some areas of Montana, dogs may be one of the chief predators of deer. Dogs kill deer, antelope and their fawns, moose and elk calves, small mammals, and other wildlife. The impacts of free roaming dogs on wildlife may include harassment, injury, or death. Although not wildlife, a report from the National Agricultural Statistics Service showed that dogs killed 40,325 sheep/lambs in the U.S. in 1994 and approximately 21,800 cattle in 1995, attesting to their latent killer instincts.