A significant amount of bark has been removed. It is possible squirrels are stripping it and using it for nest building. It is too high up for you to do anything yourself. If you are certain it is squirrels, you could call a pest control company and see if they would come out. I believe there are restrictions on dealing with wildlife. You also could try having a certified arborist come out and do an on-site inspection and see if they have any solutions. You can find one by visiting this site and clicking on Find An Arborist. You can put in your zip code.  http://www.treesaregood.org/