I live in the Mid Atlantic region and have overwintered six squirrels - so far!
I take clippings from various shrubs in my yard as well as nearby. (I take my garden snips with me when out for walks.)
I have experimented with lots of different shrubs and trees, and of course at different times of the year.
I have a Japanese willow in my yard, and right now with lots of buds it is extremely popular with my current overwintered boy Huckleberry. (Huck is still indoors,) He not only eats the buds and leaves, but often strips off all the bark. (Huck looks like he is eating corn on the cob as he moves the piece of branch back and forth and rotates it around.)
The various prior releases and wilds in my yard also spend a fair bit of time browsing. (This is a small tree with multiple trunks currently around 10' feet and almost as wide.)
Anyways, I am looking to plant some more shrubs in my yard. I do not have the space for more trees, so looking for shrubs that will not get taller than 8' (or at least can be trimmed to keep them this size).
Any suggestions as to shrubs their own squirrels (wild, overwintered, released) have particularly liked to eat are most welcome, thanks!