In the fall and winter chickadees forage on boxwood for insects and caterpillars, even if frozen. Generally, this is not a reason for concern.

Your task is to carefully inspect your boxwood looking for any caterpillars or insect nests that may be there. One relatively new (to Michigan) is the Box Tree Moth. Watch for this one as it is dangerous. The info in the links below will tell you what to look for: 

https://extension.psu.edu/box-tree-moth/

https://www.canr.msu.edu/news/what-growers-and-landscapers-need-to-know-about-box-tree-moth

Keep an eye out for this pest (moths early then caterpillars later) this spring.