For some reason, I had a bird issue during my 121 tenure--one goose right below my windshield, a flock of small gulls on the underside of the wing on rotation, some other small stuff, and a duck in an engine two weeks before I quit. I think all of the captains filled out 5200-7, as it was strongly encouraged by the airline. The FAA treats it pretty seriously, so the more information they have (especially if you reported it to tower) the less likely they are to give you a call for clarification.