The large, white bird is a species of Heron, and originally came from Africa. Nobody knows for sure, but a combination of strong winds and adventurous flying brought a few of them to northeastern South America - modernday Brazil. Very gradually they expanded their range, fitting in well with the wide distribution of large herbivores and the warming climate.
The first documented Cattle Egret in North America was 1952. In 1959 a few had reached Texas. Now they're a common sight around here, feeding in insects in very efficient groups called 'stampedes'.