At least in SD, it's not all that hard to avoid both cactus and the places you're most likely to encounter snakes. When you find a lot of cactus, turn around and hunt somewhere else. And carry a Leatherman to pull spines. Rattlers . . . avoid prairie dog towns (which don't have any decent bird cover anyhow) and rocky areas.

One of my favorite spots for birds at Ft. Pierre is a long ridge. Good grass cover on top and a ways down slope on either side. Go too far down, however, and you'll find a lot of cactus. Stay high, stay out of trouble.