The tires on a typical bike are too skinny to maintain balance at slow speed, much less get traction on a sloppy springtime trail. There's nowhere really good to carry your gun or bow, and riding while wearing a turkey vest is difficult. Most mountain bikes are painted in gaudy colors, too. That's OK if you're a spandex-wearing granola cruncher (or just riding for fun), but turkeys do not like bright, shiny things. Usually, you're just as well off to walk.