The sooty tern (Onychoprion fuscatus) is a seabird in the family Laridae. It is a bird of the tropical oceans, returning to land only to breed on islands throughout the equatorial zone.
This is a large tern, similar in size to the Sandwich tern (Thalasseus sandvicensis) at 33–36 cm (13–14 in) long with an 82–94 cm (32.5–37 in) wingspan. The wings and deeply forked tail are long, and it has dark black upperparts and white underparts. It has black legs and bill. The average life span is 32 years. Juvenile sooty terns are scaly grey above and below. The sooty tern is unlikely to be confused with any tern apart from the similarly dark-backed but smaller bridled tern (O. anaethetus). It is darker-backed than that species, and has a broader white forehead and no pale neck collar.
The call is a loud piercing ker-wack-a-wack or kvaark.