The pilot was checking cattle while flying over 'choppy' terrain at an altitude of 150 to 175 feet above the ground. He was flying to the southeast then made a turn to the northeast (downwind) and had just started a turn back to the southeast when the helicopter began to settle. The helicopter impacted uneven terrain and rolled over to the left. The pilot reported the winds were from the south southeast at 20 knots with slight gusts at the time of the accident.