The Aransas National Wildlife Refuge is famous for acting as host to a flock of Whooping Cranes in the winter (the largest such flock anywhere). But you'll see more than Whooping Cranes. There are almost 400 species of transient birds.
From Austwell, take FM 774 (FM 239 in part of town) until the stop sign, where you'll turn right. Follow the street to the end, turn right and go until you reach FM 2040, where you'll turn left. The Refuge gate is about six miles from there.