Last night, Andrew Bird stopped by the eerily silent, hurricane-stricken studio at the Late Show With David Letterman, bringing Tift Merritt, his peer in singer-songwriterdom, with him. Bird played fiddle, Merritt played guitar, stand-up bass player Alan Hampton played stand-up bass, and all three of them crowded around a single mic bluegrass-style. They covered Townes Van Zandt's immortal "If I ...