The buzzing chatter of the eastern gray squirrel (Sciurus carolinensis) is a common sound in the deciduous hardwood forest, and eastern gray squirrels were the second most commonly detected wildlife species in the first year of eMammal camera trapping across the mid-Atlantic (click here for range map). Gray squirrels can reach amazingly high densities when there are abundant resources, and forest populations typically range from 4 to 10 squirrels per 1 hectare (2.5 acres).
So many squirrels in one space means that competition for resources such as tree cavities and acorns can be intense. As we have seen in American Black Bears this competition has led to complex communication and body language. One of the main difference between squirrels and bears is that squirrels are preyed upon by several other species, from hawks to bobcats, and as a result are constantly watching for threats from other species as well as dealing with interactions with other squirrels.
Squirrels mark territory with scent and may actively defend that territory in direct interactions. Gray squirrels have two main scent marking tools, urine and scent glands near the mouth. They will frequently urinate as they move along travel routes and they often stop and rub their oral scent glands as well. When two squirrels meet they will greet each other by sniffing these oral scent glands, sometimes placing their hands on the other squirrels shoulders, which gives the appearance of kissing and hugging and has given rise to many a novelty greeting card photo.
The second main territorial marking method gray squirrels is chewing a large vertical stripe on a large dominant tree in their territory and using this visual marking as a scent marking post. All squirrels passing by this stripe will stop and smell who has been around and add marks of their own. These marks are often maintained for generations (squirrel generations that is).
Although squirrels have many vocalizations and often scold predators and people from on high, these vocalizations are used more as communication with other squirrels than to maintain territory. Gray squirrels do not use their calls to indicate territorial boundaries as birds do, but they will often chatter at other squirrels in aggressive interactions or scold predators, humans, and other intruders from above.
Eastern fox squirrels share many of these same behaviors with gray squirrels, although they inhabit a wider variety of forest than gray squirrels.
For more information and pictures about eastern gray squirrels see:
Elbroch, Mark and Kurt Rinehart. Behavior of North American Mammals. New York: Houghton Mifflin, 2011. 374 pgs.
Koprowski, J. L. 1994. Sciurus carolinensis. Mammalian Species 480:1-9.