Hunting clubs and a man who paid $350,000 for a license to hunt a black rhino in Namibia have sued Delta Airlines, saying its ban on transporting some big game hunting trophies hurts conservation efforts and violates its global obligations. In a lawsuit filed in federal court in Texas on Thursday, the hunter of the endangered black rhino, Corey Knowlton, along with the Dallas Safari Club, the Houston Safari Clubs and others said that the transport of the trophies is allowed under a strict systems of global permits and Delta must abide by its obligations.