On February 23, 2002, about 1300 Alaska standard time, a Robinson R-22 helicopter, N8353M, sustained substantial damage during a maneuvering descent about 15 miles southeast of Fairbanks, Alaska. The helicopter was being operated as a visual flight rules (VFR) personal flight under Title 14, CFR Part 91, when the accident occurred. The helicopter was operated by Quicksilver Air, Inc. of Fairbanks. The certificated airline transport pilot and the sole passenger were not injured. Visual meteorological conditions prevailed, and a visual flight rules (VFR) company flight plan was filed. The flight originated at the Chena Marina Airport, Fairbanks, about 1230. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), on February 27, the director of operations for the operator said that during a low-level animal herding operation, the helicopter descended over trees into an open area. During the descent the pilot "felt a thump." The pilot made a precautionary landing and examined the helicopter. During the examination, the pilot found the tail rotor blades were damaged. The director of operations said prior to the flight, there were no known mechanical problems with the helicopter. In a written statement provided to the IIC by the pilot, the pilot said he did not know what struck the tail rotor. He said due to his close proximity to trees and brush he believed the damage was caused by a bird strike. He said he was well clear of the trees and brush when he "felt the thump." The pilot has filed a "Bird/Other Wildlife Strike Report" with the FAA. There was no clear evidence of a bird strike presented, or found during the investigation, and the pilot in his written statement says, "...it is still unclear to me what contacted the tail rotor."