What I use, and it works great, is a good squirt of Dawn dishwashing liquid (NOT anti-bacterial) mixed into a gallon of water and poured into pesticide sprayer. Just spray the ants. The soapy water will break down the waxy coating that helps ants retain moisture. Once their protective wax is gone, the ants shrivel up and die. This works great on fire-ant mounds as well. In the case of ant mounds, you just pour the mixture over the mound, and you will see in a couple of hours all of the dead ants.
Soapy water is also good for your plants and it won't harm the chickens at all. This is a very effective, eco-friendly method.