Just a simple post today to show the differences in the breeding and nonbreeding plumage of Royal Terns. Royal Terns are “Crested Terns”, in this image the crest isn’t visible. The white on the top of this terns head indicates that it is in nonbreeding plumage.
The shaggy crest is visible in this image and the black extends from the bill to just under the eye and to the tips of the crest. In some adult Royal Terns the bill can be more red than this adult.