Heard a lone brown bobby was seen at a float near Cheung Chau but it is probably gone by now. It is an awesome seabird. I have seen it twice, first time in the Sea of Cortez near Loreto (Baja) and then saw it again last year in Muriwai Gannet Colony near Auckland. In Muriwai, a lone bird appeared out of nowhere in a gannet colony.
Hopefully the OP sees your question and comes back with a more accurate answer.
Happy hunting ????