Wildlife Damage Management, Internet Center for


Date of this Version

April 1991


The stripping of bark by eastern gray squirrels (Sciurus carolinensis) is a serious problem in England with 50 to 100% of the trees damaged in some locations (Shorten 1957). The economic consequences of such damage have resulted in much research (Kenward 1982, 1983; Kenward and Parish 1986); squirrel-induced damage to trees also occurs in North America (Allen 1943, Brenneman 1954) but is rarely of the magnitude observed in England. At least 10 hypotheses (reviewed by Kenward 1983) have been suggested to account for bark-stripping damage including: 1) reduction of tooth wear; 2) uncontrolled gnawing reflex; 3) source of nesting material; 4) water, 5) genetic mutation; 6) scent-marking; 7) displacement activity related to agonistic behaviors; 8) trace nutrient deficiency; 9) sap as an emergency food; and 10) sap as a preferred food. However, only hypotheses 6 through 10 appear to have merit (Kenward 1983). Gray squirrels in England regularly visited marking points to chip bark and sometimes urinate which suggests that some bark removal is related to scent marking (Taylor 1968, 1977). Many ground squirrels (Halpin 1985) and tree squirrels (Benson 1980, Ferron 1983) scent mark using oral glands. Fox squirrels (S. niger) frequently bite the substrate prior to scent marking (Benson 1980). Although squirrels do ingest bark and cambium (Packard 1956), some bark removal is related to scent-marking activities (Taylor 1969, 1977). Scent marking, including the rubbing of oral glands on a substrate and occasional urination at traditional marking points, is an almost exclusively adult male activity that occurs throughout the year (J. L. Koprowski, unpubl. data). Damage in urban areas may be highly visible, unappealing, and intolerable to residents. Herein, I report the characteristics of scent-marking points and discuss the extent of bark removal by fox and eastern gray squirrels at marking points with reference to preferred timber size classes in an urban parkland.