The Swainson’s Warbler is prized by birdwatchers and difficult for scientists to study because of the dense habitat it occupies across South Carolina and the southern U.S. Think lowland swamps, canebrakes, and mountainous rhododendron ravines.  Even if you bushwhack close enough, you’re more likely to hear the bird’s sweet, ringing song than catch a glimpse of it flitting through the understory. “I call it machete habitat,” said Jen Tyrrell, community science and research program manager at Audubon South Carolina. “They are in places that are thick and hard to get to, usually occupied by snakes and mosquitoes.” That secrecy has left the species relatively understudied. But a recent…