I was watching these Blue-gray Gnatcatchers a couple of weeks ago when one suddenly took flight, straight up in the air she went, up, up ,up. She finally stopped about 70 feet high in a tree and I could barely see her. I took a few photos and it wasn’t until I viewed them on my computer later that I realized she had a nest up there. They build their nests with spider webs and plant material, then they cover the outside with lichens. Brilliant camouflage! I’ve looked for the nest a few times since then with no luck.