Both rabbits and squirrels can strip bark. At that height it is probably squirrels. Animals will strip bark for nests and also eat bark for nutrition in the winter. The bark will not grow back. It's unlikely to kill your tree unless the bark is completely removed around the circumference of the tree. That will kill a tree.

You can protect trees and shrubs in winter by putting up a fence. That can prevent rabbits and deer from getting at your favorite trees and shrubs. As for squirrels, it's another matter if they can swoop down on a tree or shrub from the canopy of another tree or shrub. Even then they may be able to climb over the fence but making it difficult like that may convince them to try something easier.