A Bell 222 pilot reported losing part of his engine cowl; most likely from a bird strike.

Narrative

I departed in VMC; VFR in a Bell helicopter. After about 30 minutes of flight; I felt a bump and heard a bang sound. The helicopter continued to operate normally. There was no sign of damage or fire. I decided to return directly to the airport. I landed normally with the gear down. After shutdown and postflight walkaround; I noticed that the left engine cowling was partially missing. Upon further inspection; the Mechanic on duty found small dents in the 2 tail rotor blades. Prior to departure; the helicopter had been inspected in accordance with the Bell Helicopter Operating Handbook by the Mechanic on duty and me as the Pilot in Command. I believe the helicopter may have been hit by a bird on the left engine cowling; causing the lower 1/3 of the cowling to break and depart the helicopter. Again; no damage was visible from the cockpit during flight. The lower 1/3 of the left engine cowling broke into 3 small pieces and fell to the ground. The cowling latches were found to be closed. A method of prevention of recurrence is unknown.