Unless they have become a biting menace, or are throwing up hills everywhere, the best answer is don't. They are an important part of the ecology, so if you can stand them, do. That said, there are several levels of control:

If you can find their hills, slowly pour boiling water into them.

If you cant find their hills, get a cup of fresh orange peel, a cup of fresh spearmint, 1/4 cup olive oil. and 1/4 cup organic dish soap. Put the peel, mint and oil into a blender with a cup of water, and liquify it. Then mix in the soap with a spoon--if you put the soap in the blender, you'll get tooo much foam! Strain through cheesecloth and mix with 2 gallons of water to cover 500 sq. ft.

I believe there are beneficial nematodes available which repel ants, but I can't remember the product name!

Next level, spray with an insecticide containing a synthetic pyrethroid.

Hope all this helps!
Tug

Let the birds eat them.

Yep, that too.