Squirrels gnaw on the bark of many different tree species in winter. Grooves in the bark of maples, especially sugar maple as shown below, indicate squirrel have been extracting the sugary sap. Other areas of missing bark high in trees can indicate squirrel have been extracting the bark to use to make dreys or eating the pulp.
Fox squirrels will gnaw at lower branches and tree trunks, but these signs are more difficult to distinguish from rabbit activity.
Image Species: Maple
Web Page and Pictures By Hannah Leitheiser