I'm going to restrict myself to birds that stand at least 20" tall and whose plumage is more or less completely white. I won't include geese, ducks or White Pelicans because most people recognize these; and I won't include Whooping Cranes, because you're not going to see those unless you travel down to Aransas in the winter.
When you read about each species, it is worth paying particular attention to the comments about behavior and habitat. These often provide the easiest way to distinguish between similar-looking species.
Great Egret (39" tall)
You will see this resident bird in or around water, or flying overhead with slow wing-strokes. Its plumage is completely white, and it has a yellow bill and black legs and feet. It spends a lot of time standing motionless; when it moves, it does so very slowly and gracefully.
Snowy Egret (24" tall)
This resident is common in or around water. It has white, fine plumage with a black bill, black legs and bright yellow feet. In water, it usually moves around often and quickly, using its yellow feet to stir up prey.
Cattle Egret (20" tall)
This resident is usually found in flocks in fields and along roadsides, often with cattle or other livestock. Its bill is yellow and its legs and feet are dark. It normally has all-white plumage, but in March-July breeding birds have orange feathers on their crown, their back and the front of their neck.
Cattle Egret in breeding plumage
White Ibis (25" tall)
This resident is usually seen in water or in wet and muddy areas. It is often in a flock. Its red legs and large down-curved red bill contrast with its white plumage. In flight, it has obvious black wingtips.
DISTINGUISHING BETWEEN THE COMMON SPECIES
The White Ibis is impossible to miss because of its red bill. Also, no egret has black wingtips.
Breeding Cattle Egrets are easy to ID because of the distinctive orange patches on their plumage. However, the easiest way to tell all Cattle Egrets from the other egrets and White Ibis is by their location and behavior. They prefer to hang out in fields with livestock rather than in or around water. So if you see large white birds walking between the legs of cows or standing on the backs of bison, you're sure to be looking at Cattle Egrets.
Unlike Great Egrets, Snowy Egrets have bright yellow feet. The two species act very differently, too. Great Egrets fish/hunt standing still or moving very slowly; Snowy Egrets tend to run around in water, stirring up fish and other small prey with their yellow feet.
Little Blue Heron (24" tall)
This resident fishes in shallow freshwater. As its name suggests, it usually has all-blue plumage - and a blue bill. However, young birds have pure white plumage. Juvenile Little Blue Herons can be distinguished from Cattle and Snowy Egrets by their gray bill and dull greenish legs. Their normal habitat is also different from that of Cattle Egrets.
Juvenile Little Blue Heron
Reddish Egret (30" tall)
This resident is normally found only in shallow saltwater along the coast. Most birds have a gray body and a reddish-brown neck and head. However, at coastal sites such as Bolivar Peninsula, you may see a pure white morph of this bird. If you watch any Reddish Egret for a few minutes, its unique and very active fishing tactics will distinguish it from all other birds: Often with its wings raised, it runs about in bursts, jumps up and down, and spins around.
White morph Reddish Egret fishing
Wood Stork (40" tall)
This is not a common species and it appears in our area only in the summer, when it may be seen walking around in shallow water. It is very easily identified by its huge down-curved dark bill. Its wings are edged in black; this is not very obvious when the bird is on the ground but it is impossible to miss when the bird flies.
Two Wood Storks (with a Roseate Spoonbill)