By sunrise on an August morning, the landscaping crew at the Marathon Grasslands Preserve in Brewster County is hard at work. Plump, sandy brown bodies scamper across the gently sloping ground at this 2,700-acre preserve about ten miles northeast of Marathon, pausing where a piece of too-tall grass needs to be chewed down. Dirt flies as a digger cleans out a burrow, her black-tipped tail bouncing as she works. It’s a social bunch that touch noses as they pass one another and keep up a steady chatter of birdlike chirps. Meanwhile, a sentry keeps watch for predators from her perch on top of a mound. She stands alert, her stumpy little T. Rex arms resting on her white belly, and scans the landscape.This industrious bunch…