I was a little mystified why this bird was so agitated by my presence. As far as I knew at the time there weren't any nesting terns in the area. Then I noticed a juvenile, not in the immediate area but close enough that I guess its parent saw me as a potential threat. In recent days I've been in the same area among adults and juvies and they've been very passive. I suppose they become less protective as the young ones age and learn to fend for themselves.