Texas birdlife is strongly influenced by the incredible diversity of habitats found within its borders. The Rio Grande corridor is a great example of this diversity. From El Paso to Brownsville, this once-majestic river forms the 1,569-mile southern and western borders of Texas. At El Paso, the average rainfall is only nine inches per year compared to the 26-inch annual rainfall of the subtropical Lower Rio Grande Valley. In between can be found the magnificent Chihuahuan Desert with its mountain islands, the Stockton and Edwards Plateaus, and the brush-covered plains of South Texas.