Brown Boobies (Sula leucogaster) obtain prey by plunge dives. In order to investigate the foraging behaviour of Brown Boobies underwater, we attached acceleration data loggers to chick-rearing Brown Boobies at Nakanokamishima Island in Japan. We documented, for the first time, Brown Boobies performing many rapid and shallow V-shaped dives and some W-shaped dives during the daylight period. The average and maximum dive depth and duration were 1.03 m and 3.81 m and 1.83 s and 21 s, respectively. Furthermore, Brown Boobies used buoyancy to ascend to the water surface. Our data suggest that Brown Boobies mainly depend on shallow-plunging, contrary to the pursuit divers such as gannets, due to their ecological and/or physiological constraints.