Crested Tern (non-breeding plumage)

Thalasseus bergii, known as the "crested tern" in Australia, is a tern in the family Laridae, which also includes gulls and skimmers. It nests in dense colonies on coastlines and islands around the continent. There are five subspecies globally, but the local subspecies T.b.cristata, ranges from Australia to PNG, and into southeast Asia. During the breeding season, the adult has a distinctive black cap with a long crest, white neck and underparts, and a grey back and upperwing. In contrast, the non-breeding adult has a white crown with limited dark spotting, but its hind-crown remains black. The large bill is greenish-yellow to yellow, and the legs are black. The juveniles primarily differ from the adults in having heavily mottled or barred brown upperparts. Everything else you could ever want to know about this species can be found at the reference links. Wikipedia is extensive. PS: The barnacles seen in these images are Tesseropora rosea, aka rose-coloured barnacles.