On July 7, 2006, about 0910 Hawaiian standard time, all five main rotor blades of a Hughes 369D, N611WA, struck a tree during a hover, near Kihei, Hawaii. Windward Aviation, Inc., operated the helicopter under the provisions of 14 CFR Part 91 as an Aerial Capture Eradication and Tagging of Animals (ACETA) operation for the Tri-Isle Resource Conservation and Development Council (Tri-Isle). The helicopter sustained structural damage to the all five main rotor blades. The pilot and two passengers were not injured. Visual meteorological conditions prevailed for the local area ACETA flight, and a company visual flight rules flight plan had been filed. The flight departed Kahului Airport (OGG), Kahului, Hawaii, about 0810. In the pilot's written statement, he reported that the purpose of the flight was to conduct an aerial reconnaissance and eradication within prescribed boundaries of a preserve above Kihei. After an hour of flight, an animal was identified within the prescribed boundaries. The pilot stated that he was asked to land by personnel from Tri-Isle so his passenger could recover the animal and transport it to the ground crew at an alternate site. He reported that the landing zone consisted of rolling terrain with thick low trees, high grass, and lava rock outcroppings. During the landing phase of the flight, about 15 feet above ground level (agl), the main rotor blades contacted a tree located on the right rear side of the helicopter. After the impact, the pilot repositioned the helicopter to an alternate landing site about 100 feet from the original landing zone. He shut down the helicopter, notified the operator, and waited for maintenance personnel to arrive and assess the damage to the helicopter. The Director of Maintenance inspected the main rotor blades and determined that the helicopter could be flown back to OGG. According to the pilot the decision to land was done while he was in a hover, and had not been part of the pre-brief prior to departure. Windward Aviation, Inc., maintenance personnel removed the main rotor blades and inspected them. Maintenance personnel determined with the use of the helicopter's maintenance manual that the dents/depressions of all of the main rotor blades were beyond serviceable limits and could not be repaired. Maintenance personnel measured the depth of the dents/depressions: Blade E116 - 0.090 inch at station 130 Blade D315 - 0.040 inch at station 130 Blade D307 - 0.080 inch at station 140 Blade E117 - 0.200 inch at station 124 Blade D316 - 0.160 inch at station 124