Daniel Walters photo On a January outing to Turnbull Wildlife National Wildlife Refuge, Ben Goldfarb scouts for signs of beaver activity. W ildlife signs can be subtle, even to an expert tracker. A few errant droppings of dried scat, a hint of a hoof-print, or the trampled brush. But beavers? Beavers, oversized buck-toothed rodents that they are, are not known as subtle animals. Beavers don't just leave poop or prints. Beavers redraw maps. Beavers topple trees. Beavers raise rivers. Beavers build walls. Beavers change topography. Still, as we walk through the trails of Turnbull National Wildlife Refuge on a crisp January morning, environmental journalist Ben Goldfarb knows that beaver signs go beyond gnawed tree stumps.