Dave,
I thought he was talking about the Snowy Egret.
Their primary diet is fish although I understand they will eat insects, frogs ect.
Ml,
Is this "cattle bird" you refer to also white?
Ok James, acording to thess websites it could either be a "Cattle Egret" or "Snowy Egret"
Both are said to eat fish but fish are the Snowy's main dish.
Cattle Egret:
DIET:
The diet of cattle egrets consists of insects particularly grasshoppers and they avoid bumble bees, wasps, and yellow jackets. They expend less energy in catching their food by following cattle and farm machinery and catching the insects that are flushed. In aquatic habitats they eat frogs and fish. Captive egrets in zoos are given smelt, mealworms, and crickets to eat.
http://www.honoluluzoo.org/cattle_egret.htm Snowy Egret:
The snowy egret runs after its food. It eats shrimp, minnows and other small fish, crustaceans and frogs. It often feeds in groups.
http://www.nhptv.org/natureworks/snowyegret.htm I believe I would try to ID them but like Dave says that many birds can cause damage to vegitation with their droppings.