A fish finder for birds: route-dependent foraging behavior of the brown booby (Sula leucogaster) on a passenger ferry

Abstract This manuscript reports a novel case of route-dependent foraging behavior in the brown booby ( Sula leucogaster ), based on visual observations from a passenger ferry between Chichijima and Hahajima Islands, Ogasawara, Japan. On four dates in 2017, the number of accompanying boobies and their plunge-diving behavior were recorded using only handheld counters. More birds and dives were observed on routes departing from the nesting-rich Hahajima, with peak activity mid-route. These findings suggest that the ferry acts as a “fish finder,” flushing prey such as flying fish for the birds to exploit. The study highlights how low-tech observations from public transport can provide valuable behavioral insights and underscores the potential of citizen science in seabird ecology.