The helicopter collided with trees and terrain while maneuvering at low altitude in mountainous terrain. The pilot reported that he and two observation crewmembers were flying a mission for a state agency involving the aerial capture and radio collaring of deer in mountainous terrain, where the helicopter was required to be flown slightly above the tree tops. While they were looking for animals, the pilot flew toward the steep side of a north facing ridge and started flying a grid search pattern. At midslope, on an easterly heading, the pilot turned right facing upslope and into the sun. After completing the turn he maneuvered the helicopter into the shadow of the ridge, and then realized that there was not enough room to maneuver due to the proximity of the tree tops. The pilot attempted to slow the helicopter before the nose and main rotor contacted the trees. The helicopter came to rest on its right side, facing uphill. The main rotor hub and blades were located approximately 12 feet in front and to the right of the helicopter.