Bentsen Rio Grande Valley State Park in Mission is one of the top birding sites in the nation. Also it's the headquarters for the World Birding Association. Lots of campgrounds around the park. They have a free (with park admission) shuttle to ride you through the park, lots of feeding stations to attract the birds,and knowledgeable and helpful volunteers and staff to help you find and identify the birds. They have had three years of drought and that has affected the bird populations, but there's still lots of birds and it's still one of the best sites for birds you won't find anywhere else in the U.S.