Two helicopters were conducting low-altitude wildlife capture operations in mountainous terrain when they collided mid-air. Both helicopters were substantially damaged; the pilots and passenger were uninjured. The pilots and passengers briefed their operational plan prior to departing. The first helicopter (N74730) was assigned to a northern sector and would perform operations starting on the north edge of that sector, working south. The second helicopter (N996NR) was assigned a sector bordering the southern boundary of the north sector and would begin its operations at the southernmost portion of its assigned sector, working north. The pilots each planned to meet at a fuel truck located near the common border of the two sectors. The operational area was in remote terrain that included hills, canyons, and ridges. The mission required the helicopters to operate close to/at ground level and included periodic landings. Approximately one hour after operations began, both helicopters arrived in the same area near the sector boundary, where they continued to independently conduct the low-altitude operations. The pilot of the second helicopter had just dropped off his passenger to complete a wildlife capture and had become airborne again. Both pilots reported they were airborne and descending slightly, when the pilot of the first helicopter saw the other helicopter converging head-on. The pilot of the first helicopter quickly applied full up collective control to attempt to climb above the flight path of the converging helicopter, and as they passed the helicopters collided. The collision resulted in substantial damage to the tail section of the first helicopter. The pilots stated they believed the accident could have been avoided with better radio communication. Additionally, the pilots reported that the terrain’s effect on radio transmissions and the operational workload prevented continuous and unreliable communication between the helicopters; therefore, they relied on see-and-avoid techniques to ensure safe separation. The pilots of both helicopters reported no mechanical malfunctions or anomalies that would have precluded normal operations.