This Is A Large Tern, Second Only To Caspian Tern But Is Unlikely To Be Confused With That Carrot-billed Giant, Which Has Extensive Dark Under Wing Patches. Royal Tern Has A Long Yellow Bill, Pale Grey Upperparts And White Underparts. Its Legs Are Black. In Winter, The Black Cap Becomes Patchy. Juvenile Royal Terns Have A Scaly-backed Appearance. The Call Is A Characteristic Loud Grating Noise Like A Sandwich Tern. Photo