They'll do that - your feeder's clearly a place where birds gather (and to hawks, that's a few meals). My advice is to take the feeder down for a few days. The hawk will move on when he figures out the birds are elsewhere.
The most common hawks in north Texas are pictured here. The Sharp-shinned and Cooper's look very similar - the banding on the tails is the key. Both are about the size (although leaner and smarter) of an ordinary Dove. The Red-tailed is larger and the coloring is extremely variable.
Contrary to what some store clerks will tell you, putting up fake owls and plastic snakes doesn't scare away hawks or any other bird for more than five minutes. Save your money! Things that move randomly are the only things that catch their eyes.