The pilot was conducting a predator control mission when he spotted wild hogs in an approximate 20-acre field of Salt Cedar trees. The pilot made a quick stop at an out-of-ground effect (OGE) hover in an attempt to move the hogs out in the open. The pilot stated that the low rotor RPM horn and light activated. He immediately stopped to regain rotor RPM. As the aircraft approached the edge of the trees towards an open field, the wind stopped and the rotor dropped to approximately 90 percent. The pilot observed an increase in airframe vibration followed by a hard left roll. The helicopter main rotor blades struck the ground in a 90-degree bank and came to rest on its left side. The pilot was not injured and the passenger sustained minor injuries. The pilot stated that the approximate gross weight at the time of the accident was 1,370 pounds. The helicopter performance charts indicated maximum weight for out of ground effect hover was 1,320 pounds for the weather conditions.