The pilot stated that he had conducted five normal practice takeoffs and landings in the airport traffic pattern. During the landing flare for the sixth landing, he observed a flock of birds at the end of the runway and attempted to touch down and stop the airplane in a shorter than normal distance. The pilot stated that the airplane touched down hard and porpoised several times. On the final touchdown the nose gear collapsed. A Federal Aviation Administration inspector, who examined the airplane after the accident, observed substantial damage to the engine firewall. The pilot reported to the FAA that there were no mechanical malfunctions or anomalies with the airplane.