Squirrels Communicating Over the Bridge

Northern Spicebush (Lindera benzoin) branch serving as a bridge for
Eastern Gray Squirrel (Sciurus carolinensis) to cross over a
small spring seep in a Connecticut woodland.
Photo by James Fischer

Jared Franklin and I were surveying the Apple Hill vicinity.  We came upon an interesting observation of Eastern Gray Squirrel that I would like to share with you.  All of us at times observe squirrels navigating through the tree canopies over our heads.  You can observe this behavior in many of our woodlands at White Memorial.  I often see squirrels using the trees canopies a bridges over the wood roads, especially when I am leading a large group of people on walks or when I am walking with a dog.  It appears to me that the squirrels are using the intermingled branches of several individual trees as another thoroughfare through the woods.  What a great way to avoid potential threats while still making their way through the forest.  These canopy through-ways bypass threats from both the ground and to a certain extent the air because there are so many branches that could shield a squirrel from the approach of a aerial predator.  This connectivity has always intrigued me because I wonder if these thoroughfares could be limited to the use of only certain individual squirrels.  Or could there be potential tolls for the use of these thoroughfares?  Similar to the way people pay a fee to use the state government turnpike or through-way road systems.

The evidence that I have had trouble collecting were ways that squirrels could communicate that these bypasses were frequently used by squirrels.  Jared and I observed a sturdy Northern Spicebush branch leaning over a small wet area.  The wet area was sparsely vegetated, which left little cover for a squirrel to use for protection.  What drew our attention to how important this branch was to the local squirrel population was the tell tale bites found in the bark of this branch.

Eastern Gray Squirrel bites marking this branch serving as a bridge.
Photo by James Fischer

Eastern Gray Squirrels wound the bark on branches and tree trunks to serve as a visual cue to other squirrels.  They will also rub areas of their bodies that have chemical scent patches or urinate on the marks so that there is a olfactory stimulus to insure the message gets across.  These squirrels are saying something on this branch and whatever it is they are saying it often!  Notice how some of the wounds look older than the others.

Wow!  I wonder if this how they do it the tree canopies?  Certain individuals may wound and scent mark specific trails that communicates that it is their trail by using their trail-blazes.  Maybe the rest of their social structure could explain who and why certain squirrels use these pathways.  Could social and genetic relatedness explain why some animals use the canopies byways?  Could some canopy trails become legacy resources used by several generations of squirrels?  So many questions...