I was told that turkeys move into the open when it rains because their feathers don't shed water well if they're displaced. In the open, with no brush touching them, their feathers will shed water like a canvas tent, but like a canvas tent, if they're brushed against by anything, they'll start leaking and the bird will get wet. Also, that rain will cause bugs to come off the ground and cling to vegetation where they are easier targets.