Do frigate birds fly at night?

Strange question, never thought about it lol. Frigate birds migrate alot, thus meaning that yes they do have to fly at night.

I would say that their vision would not be the best however.

Aiab is correct. Frigates need to migrate, and most birds migrate throughout the night and day. They may rest for a short while, feed, and excrete/urinate though, but most of the time they are in flight.