The pilot stated that he was flying his tailwheel-equipped airplane at 400 feet above ground level when he spotted two bears in a swamp. He said that as he was turning left to look at the bears, the nose of the airplane dropped rapidly, and the airplane descended vertically. During the pilot's efforts to recover from the aerodynamic stall, the airplane impacted terrain, sustaining substantial damage to both wings and the fuselage. The pilot reported that there were no preaccident mechanical anomalies with the airplane.