During the takeoff roll, a hawk struck the airplane's windscreen and then struck the vertical stabilizer and rudder. The airplane veered to the right, exited the runway and nosed over. The airplane sustained substantial damage to the vertical stabilizer and rudder. A postaccident examination revealed that the hawk had lodged between the vertical stabilizer and rudder which interfered with the flight controls and deflected the rudder to the right. There were no preaccident mechanical malfunctions or failures with the airplane or engine that would have precluded normal operation.