The Blue-gray Gnatcher is a common bird in Central-Coastal California in the summer. It flits around in the brush wagging and lifting its tail which startles insects causing them to fly to become a tasty morsel for this bird. This photo is of a male because of the blue “V” on its forehead.
If lucky, you will encounter these birds nest building. They gather caterpillar and spider silk and use it to fasten fragments of lichens into a small thimble which becomes the nest. The nest looks like a bump on a tree’s branch and it’s impossible to know if it’s a nest unless you see an adult fly onto it.