Bark Stripping by Fox, Gray, Red, and Ground Squirrels

Fox squirrel barks tripping. Photo by Erin BauerFox squirrel bark stripping. Photo by Erin Bauer

Identification and Causes

Damage to Tree Barkstripped bark

 Fox squirrel (Sciurus niger) and gray squirrels' (Sciurus carolinensis) damage to tree bark (called bark stripping) can be quite severe. See photo at right by Dallas Virchow.

We have recently heard from a gentleman in Pennsylvania that red squirrels (Tamiasciurus hudsonicus) also strip bark. We would love to hear from anyone who has had similar experience.



Identification of Bark Stripping

  • Fox squirrels exist in the middle portion of the continental U.S. (Note the range of gray and fox squirrels overlap).
  • Gray squirrels exist in the Eastern portion of the continental U.S.
  • Typically, strippings are 1/2 inch wide and 3 to 6 inches long. Other small limbs branches of 1- to 2-feet in length and 1/4 to 1/2 inch diameter are clipped and dropped to the ground.
  • Squirrels prefer to strip branches that are horizontal, but have been known to strip trunks too. The damage can be extensive.
  • Red squirrels like to clip branches of maples (particularly sugar maples) to get at the sweet sap.
  • Bark stripping usually occurs in late winter. But it can occur in the spring if trees don't produce mast.
  • Incisor Widths--These figures encompass the range in the width of teeth between upper and lower incisors and between male and female squirrels.
    • Gray squirrel (Eastern)--1.17 to 1.74mm
    • Gray squirrel (Western)--1.19 to 2.25mm
    • Fox Squirrel (Eastern)-- 1.40 to 2.30mm
    • Red Squirrel
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Types of Trees Stripped

  • Ash (Boise, ID)
  • Atlas Cedar (ID)
  • Autumn Olives (NE)
  • Bald Cyprus (Cleveland, OH, 2013)
  • Cedar, (Tacoma, WA, Sept 7-21, 2013) western gray
  • Cedar, Washington Red (WA June, 2010; Puyallup, WA Nov 2013) western gray squirrel
  • Corkscrew Willow (OR) December, 2008
  • Elm (San Mateo, CA) May, 2009 Damaged branched up to 2-inches in diameter; Austin TX 2009-2012.
  • Elm (Visilia CA; 2010) ground squirrel stripped 2 branches
  • Ginkos (TX)
  • Gingko Biloba (Visilia, CA; 2010) ground squirrels
  • Globe Willow (ID)
  • Hackberry (NE)
  • Honeysuckle (NH) (Gray Squirrel) Winter 2008/9
  • Honey Locust (NE)
  • Japenese Maple (OR Dec, 08; Cupertino, CA July, 10).
  • Lilac Bushes (Jan, 2010; Syracuse, NY May, 2014).
  • Linden--Small Leaf (Ontario, Canada, stripped in Mid-November, 2008; Rochester, NY; March, 2010. New Hampshire; Throughout year)
  • Locust Trees (red squirrels Kansas July, 11)
  • Maple (FL, MN, NE July, 09; stripped 2 ft sections of trunk, Austin, TX, May, 2012)
  • Maple, Japanese (TX)
  • Maple, Large Leaf (OR/WA, 2010)
  • Maple, Red (NE)
  • Maple, Sugar (MN)
  • Maple, Vine (WA, June, 2010) Western Gray Squirrel
  • Mulberry Tree (fruitless, OK May/June 2009; water available- Vallejo, CA July, 2011; water available; fruitless-Carrollton, TX May, 2014 )
  • Oaks--various varieties (TX; NH May, 2010)
    • Pin Oak
    • Live Oak (DFW Airport, TX, June, 2009; Austin, TX, May, 2012)
    • Red Oak (25 year old red oak; Stripping has occurred mostly in the crooks of the limbs where they meet the trunk. San Antonio TX. June, 2010.
  • Pecan (GA June, 2009)
  • Pines--various varieties (Southern GA, July 2011)
    • Loblolly  (Southern GA July, 2011;)
    • Bark stripping by a squirrel. Photo by Pam Morawski.
    • Longleaf?  (Southern GA July, 2011;)
    • Slash (Southern GA July, 2011;)
  • Poplar (GA)
  • Poplar (Tulip Variety; OH, Spring, 2013)
  • Red Wood (Northern CA April, 2011)
  • Russian Olive (Milton, Ontario)
  • Siberian Elm (Denver, CO, June, 2013)
  • Sycamore (NE)
  • Willow, Globe

 

 

Why Squirrels Strip Bark

There are essentially several theories.
  1. Pregnant females often don't eat just prior to giving birth. Bark stripping may be their way of responding to the pain.
  2. Searching for water (although this theory has been weakened by observing that squirrels strip bark even when during a wet spring).
  3. Searching for food by eating the inner bark layer. Remember, just because a squirrel has access to food quantity, doesn't mean it is obtaining sufficient nutrients. Bark stripping by a squirrel. Photo by Pam Morawski.
  4. Squirrels may strip bark simply because they enjoy doing it. Just like some people enjoy doing less than ordinary activities, some animals may also be less than ordinary.
  5. We may never have a complete understanding of why bark-stripping occurs.

Squirrels also damage trees by limb/twig cuttings

  • Timing: Typically occurs in Spring (nest construction) and Fall as in (crop gathering). Pin oaks seem to be typically hard hit (Source: Jerry Pickel of PA).
  • Tassel-eared squirrels use the twigs to feed on the nutrients found in the cambium and subcambium layers of pine and firs (Source: Richard Wadleigh).

Solutions to Stop Bark Stripping

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