They chase boobies and rob them of their catch. Using their speed and maneuverability, the frigatebirds harass their victims until they regurgitate their stomach contents. Though they do not swim and cannot walk well, they can stay in flight for days landing only to roost or breed.
Unlike curious boobies, frigatebirds are shy and hard to photograph.
photo by Sylvia Ramos, from http://www.tonjiandsylviasbirdlist.com/Birds-of-the-Philippines/Frigatebirds/