Most people know that mule deer numbers have declined in much of the West since 1990. During the 20th century, the first century of North American wildlife management, many big game populations had a tremendous increase from extremely low numbers in the early 1900s. So, there was understandably not a lot of research on declines in mule deer populations. But, the 1990s brought a downturn that alarmed western hunters and wildlife agencies. In the Piceance Basin of NW Colorado (GMU 22), which is winter range for the largest mule deer herd in Colorado, deer population density declined by 2/3 from the 1980s to the early 1990s. The need to understand the dynamics of mule deer population levels suddenly became critical.