While walking at the Morton Arboretum, I saw 2 Blue-gray Gnatcatchers flying to the same area of a tree. Further inspection revealed that they both were building a nest. How cool is that? Every few visits to the nest, one (I assume the female) would sit in the would be nest, wiggle a bit, and work on the side of the nest. I was fortunate to catch her with a piece of grass or something in her mouth and inter-twining it in the nest.