Royal Tern (Thalasseus maximus)
Gulls and Terns are not the easiest to identify. At least for me :). The main criteria is that Royal Terns (Thalasseus maximus) has a thicker and more robust beak than the Elegant Tern (Thalasseus elegans).
Terns are pretty amazing to watch in flight, their aerodynamic, their speed and their agility are really impressive.