I wonder if too much sun in your eyes/squinting for a long time might also be a cause. I always wear sunglasses, even in the rain, so I don't know.

I agree about the pigtails -- I always wind up loosening my ponytail during a long ride, and sometimes have to loosen my helmet a bit also.

If lisag is only getting them after big event rides but not after long training rides, then stress might be a factor. Changes in sleep and eating schedules can also contribute. I would also look at diet, specifically any foods you eat during the ride that you don't normally eat, since some foods and drinks can trigger migraines. It can also be a combination of triggers.