Unfortunately, the solutions to your problem are not simple. We would suggest the following:
Hawks are a federally (and often state) protected species. Utmost caution must be used to prevent harming the birds as such action would be a violation of federal law. Lethal control of hawks can only be performed with a permit granted by the federal government and often state wildlife agencies. To apply for a permit download the application at Bird Control it will be located at bottom of page.
You can learn more about the habits of hawks and other birds of prey as well as methods for controlling them at Controlling Birds
It is important to note that hazing has limited site uses due to the sound, explosions and local rules. It can be effective in the short term. The first principle is, the quicker birds are discouraged from a roost the more likely it will be effective. Second, the more intense and diverse the hazing (ie using more than one technique) the more effective the hazing will be. Visit Bird Hazing for details on hazing birds.
Don’t waste your time with ultrasound. There is no peer-reviewed evidence that it works except to repel money from your wallet.
Second, cutting tree branches to prevent roosting or installing spikes or other physical deterrents.
Third control prey species. If you have a bird feeder, perhaps it would be a good time to take it down so that the prey would move on. With the prey gone, the hawk will leave.
I would love to get some bird damage pictures if you can get good contrast and an object in the image to show relative size. 3 megapixels or greater are most appreciated. My e-mail is firstname.lastname@example.org
Disclaimer: As with any activity, remember that animal damage control comes with its own risks and problems which can include but are not limited to legalities, health threats, and personal liabilities. Be sure to follow all state laws governing wildlife and make sure you have a thorough understanding on how to resolve the animal damage complaint. My advice is only as good as your understanding of me and my understanding of your situation. If you have any questions be sure to write back.