Two hours before dawn, and the valley's blast-furnace heat was already intensifying. Four men padded along a dirt road. A half-mile away, flatbed trucks made their way along Highway 83, a narrow strip of asphalt near the U.S.–Mexico border, angling north and west from the Gulf Coast.The men raised their binoculars briefly to watch a satellite move across the horizon. "You think they threw us a red herring?" The men had been told they could see a common poorwill here, but after a few minutes of searching, Michael Manson was beginning to wonder. The tip had come from a competitor. "No," he said, answering his own question. "They wouldn't do that."Not even to gain an edge in what has become the Ironman of birding marathons: the Great Texas Birding Classic.Each spring along the state's 500-mile Gulf Coast, from Brownsville to the Louisiana border, teams of three to five birders battle for five straight days—sleeping optional—to see who can bag the most bird species. At stake are...