The pilot was landing a tailwheel-equipped airplane at an off airport site, adjacent to a small stream. He said that he approached the site from an upstream direction, and during touchdown the airplane landed hard, bounced, and he aborted the landing. During the second landing, he approached the site from a downstream direction, and during the landing roll, he discovered that the airplane's tailwheel was missing. The airplane sustained substantial damage to the fuselage. In his written report to the NTSB the pilot noted that after landing, he discovered that there was a slight breeze from an upstream direction. The pilot reported that there were no preaccident mechanical anomalies with the airplane. In the recommendation part of his written report, the pilot noted that the accident might have been prevented if he had taken more time to verify runway and wind conditions before landing, and operated the airplane at a lower gross weight.