The sock, well that is how I often describe a Bushtit nest.
I first noticed this one almost two weeks ago while it was still under construction. Unfortunately it was windy that day and they were not active coming and going with nesting material. On returning today the nest was finished.
These elaborate hanging nests are constructed of moss, lichen, spider webs and other plant material. While I could not capture construction activity, the Bushtits were active around the nest.
One of natures little marvels I enjoy finding and watching each year.