Mystery Bird: Crested Tern, Thalasseus bergii

Obviously a tern, this looks to be one of the Crested Terns: grey upperparts, white underparts; shaggy black crest which recedes in winter; long, sharp bill... the yellow bill identifies this as a Greater Crested Tern, Thalasseus bergii (differentiated from the similar Lesser Crested Tern, Thalasseus bengalensis, which has an orange bill)... the "peppered" crest shows this to be a non-breeding adult

Because of range, this must be T. b. cristata (distributed throughout the eastern Indian Ocean, Australia and western Pacific Ocean)

non-breeding Thalasseus bergii cristata

Thalasseus bengalensis (Lesser Crested Tern- note orange bill)

hmmm, a quick note on the change in taxonomy Grrl... I would maintain that the biological nomenclature for this bird should be Thalasseus bergii and not as you have above: the Greater Crested Tern was originally described as Sterna bergii by German naturalist Martin Lichtenstein in 1823, but was moved to its current genus, Thalasseus, after mitochondrial DNA studies confirmed that the three main head patterns shown by terns (no black cap, black cap, black cap with a white forehead) corresponded to distinct clades... please see the research (available as a PDF) below:

Bridge, Eli S.; Jones, Andrew W. & Baker, Allan J. (2005). "A phylogenetic framework for the terns (Sternini) inferred from mtDNA sequences: implications for taxonomy and plumage evolution". Molecular Phylogenetics and Evolution 35 (2): 459â469.