Sciurus niger

(fox squirrel)

Image Caption:
A branch brakes, causing a fox squirrel to lose his footing for a brief second.   He rightened himself, but such a misstep occasionally causes a squirrel to fall from high branches.  Usually after a fall, a squirrel will run right back up the tree after a brief moment of surprise.   If a human were to sustain a similar fall, the femur, for example would have to sustain a load of more than 3.7 times that of a squirrel’s femur per cross sectional area (see Note), greatly increasing the possibility of a fracture.  Thorington found less than five percent of sixty-five squirrels examined had healed long bone fractures.

<<  Fall Related Fractures  >>

Fox Squirrel (Sciurus niger rufiventer) Lost His Footing

The load differences was computed by first determining the cross sectional area of the midshaft femur.  The human femur measurement was averaged based on data from Ziylan and Murshid (2001), and the squirrel midshaft cross sectional area was determined by measuring a diameter of 5.2 mm on a specimen.  The cross sectional area was compared to average mass.  Squirrel average mass was taken from Hayssen (2008), and human average mass was average based on United States male and female 20-74 year-old masses from Ogden, C. L., Fryar, C. D., Carroll, M. D.,  and Flegal, K. M. (2004).  Due to the differences in weight distribution between squirrels and humans, the differences in load per cross sectional area is just a ball-park representation of a squirrel’s increased resistance to fall related fractures.  

Works Cited:

Hayssen, V.  (2008).  Patterns of Body and Tail Length and Body Mass in Sciuridae.  Journal of Mammalogy.  89(4):852-873.

Ogden, C. L., Fryar, C. D., Carroll, M. D., & Flegal, K. M.  (2004).  Mean Body Weight, Height, and Body Mass Index, United States 1960-2002.  Advance data from vital and health statistics; no 347. Hyattsville, Maryland: National Center for Health Statistics. 2004.

Thorington, R.W., Jr. (1972.) Proportions and allometry in the gray squirrel, Sciurus carolinensis. Delaware Museum of Natural History.

Ziylan, T. & Murshid, K. A.  (2001).  An Analysis of Anatonlian Human Femur Anthropometry.  Selcuk University, Konya.

Image Location: United States, South Dakota, Brookings
Image Date: 2008DEC06

Image Species: Sciurus niger rufiventer

Large Image: (EXIF information is accurate, stamped in UTC time).

Web Page and Pictures By Hannah Leitheiser
Updated: 2009AUG07