one of many

On my morning walk I witnessed a whole flock of these little gray birds dive into a single bush. I thought it would be easy to get a good capture of one or two of them since there were so many, but I was oh so wrong! They are masters of disguise and quick movements.
At first I thought they might be pygmy nuthatches, since they are small and gray and known to travel in groups. But on closer inspection I knew that was not the case. I was stumped!
But my personal professional birder advised me that it is a Bushtit :-)