- Habitat loss and fragmentation: Gray wolves rely on large, contiguous areas of habitat for hunting, raising their young, and dispersing. As human populations grew, they encroached on wolf habitat, fragmenting it into smaller and more isolated areas. This put great stress on wolf populations, making it difficult for them to find food, mates, and suitable denning sites.
- Hunting and trapping: Wolves were historically hunted and trapped because they were seen as a threat to livestock and human safety. In the 19th century, government-sponsored extermination campaigns were carried out against wolves, resulting in the near-annihilation of the species in many areas.
- Disease: Disease outbreaks, both natural and human-caused, can decimate wolf populations. One of the most devastating diseases to affect wolves was canine distemper, a virus that is also deadly to dogs. Canine distemper outbreaks in the late 1980s and early 1990s killed thousands of wolves, particularly in the Northern Rockies.
- Illegal killing: Wolves are still illegally killed today for various reasons, including hatred, fear, and mistaken identity. This illegal activity can have a significant impact on wolf populations, particularly those that are struggling to recover.
As a result of these factors, gray wolf populations declined drastically throughout the 19th and 20th centuries. By the mid-1960s, gray wolves were listed as endangered throughout the contiguous United States. However, thanks to conservation efforts, wolf populations have begun to recover in some areas. In the lower 48 states, wolves are currently found in the Northern Rocky Mountains, the Great Lakes region, and the Pacific Northwest.