Here are two shots of the same bird, seen in western Minnesota in early August, showing how different they look depending on whether they coil or extend their necks.
When they fly, their black legs trail out behind them and they hold their necks deeply coiled, or tucked.
Egrets, herons and the more secretive bitterns are all part of the family Ardeidae. The Sibley Guide notes that the great egret's combination of long yellow bill and black legs is unique among the herons and egrets.
The snowy egret, whose range overlaps a fair amount with the great egret's but is not often seen in Minnesota, is similar but smaller, with somewhat lacier plumage, black-billed and yellow-footed (they look as if they are wearing yellow rubber gloves). We saw one or two of these in northeastern South Dakota the same weekend we saw the great egret shown here.