A single guy with a decent hunting rifle, good vantage point, and a couple dozen boxes of ammo could easily take out hundreds upon hundreds of them.
A single guy can't watch his own back. At the very least, people should travel in groups and while one person does the sniping, one or two others serve as lookouts.
That's why I can't believe Otis was out there hunting on his own. To hunt, you need to concentrate your focus on your prey. How can you do that, worrying that something else is concentrating on you as prey?