This is an adult Great Egret..
A large white heron, the Great Egret is found across much of the world, from southern Canada southward to Argentina, and in Europe, Africa, Asia, and Australia. It’s the largest egret in the Old World, and thus has garnered the name Great White Egret. In the New World, however, the white form of the Great Blue Heron is larger. In the United States, the Great Egret used to be called the American Egret but that was hardly appropriate, since its range extends beyond the Americas and indeed farther than other herons.