The video is good, but the easiest place I found to do it is just after that part. When you first get to the marketplace with the chickens, it's a bit too chaotic - there's hordes of enemies shooting at you, the chickens are all spaced out, and most of them will be dead after the firefight. However, after the first battle, hang right and move into the next part of the market. At the end of the alley, there are five chickens together, and another two or three to your left. Just grenade the five, and then turn and shoot the ones next to you. Simples!