High Quality Content by WIKIPEDIA articles! The Brown Booby (Sula leucogaster) is a large seabird of the booby family, Sulidae. The adult brown booby reaches about 76 centimetres (30 in) in length. Its head and upper body are covered in dark brown, with the remainder being a contrasting white. The juvenile form is gray-brown with darkening on the head, wings and tail. While these birds are typically silent, bird watchers have reported occasional sounds similar to grunting or quacking.