What happens to a squirrel when it falls out of a tree Part II? An experiment

I’ve been much delayed in writing this post…. largely because, strap in, its sort of a wacky ride.  About a year ago, in the squirrelologist lab, we had a discussion about squirrels falling out of trees.  A few students and I have witnessed over time squirrels falling out of trees–about 30 or 40 feet high–bouncing on the ground, getting up, and running off, seemingly fine.  One student saw saw a squirrel fall of a utility wire, land on the road, and run away, seemingly fine.  We have been curious at what point these falls become lethal.  There is some speculation that squirrels use their tails as cushion.  However, Forsman and Otto (2006) put together an excellent paper on squirrel accidental falls, indicating that squirrels most commonly land in the “spread eagle” position.  In fact, out of a massive sample of one, we too have witnessed a spread eagle landing that resulted in a fatality and blogged about it.

This curiosity led to a long planned experiment to assess the worse case scenario of accidental squirrel falls.  We collected three dead squirrels that died of natural causes.  We then went onto the roof of a building on campus and dropped these squirrels from the room.  To be clear–WE DID NOT DROP LIVE SQUIRRELS FROM THE ROOF. THESE SQUIRRELS DIED OF NATURAL CAUSES AND WE COLLECTED THEM.  We dropped one from 40 ft and two from 55 ft.  Afterwards, we immediately x-rayed them in a lab here on UNE’s campus.  This 15 foot elevation delta appears important.  The 40 ft fall caused a single fracture at the end of the rib cage.  We dissected this individual to confirm the x-ray–and indeed this was the case.  The other two squirrels did not fare as well.  One suffered serious rib cage damage and an oblique fracture of the right tibia and fibula.  The second 55 ft also appeared to have rib fractures and a pelvic fracture on the right side involving the ilium, pubis and ischium.  This small experiment suggests that squirrels can survive falls from heights ~40ft and less, but might higher become fatal.  Very interesting stuff.

Forsman, E.D. and I.A. Otto. 2006. Healed fractures and other abnormalities in bones of small mammals. Northwestern Naturalist 87:143-146.

Rocket, Sarah and Sharleen dissect a squirrel to confirm bone injuries and see if any organs were impacted after falling 40 feet.

Rocket, Sarah and Sharlene dissect a squirrel to confirm bone injuries and see if any organs were impacted after falling 40 feet.

Leave a Reply