Self-righting in squirrels during unexpected falls – towards the crucial function of bushy tails in arboreal mammals

2021

Conference Paper

bio

Arboreal mammals navigate a highly three dimensional and discontinuous terrain. Tail use has been observed in many species and despite specializations, fractures from falls have been observed for example in primates. Among arboreal mammals, squirrels are widely observed to be among the most maneuverable. A recent video on YouTube went viral that showed squirrels (Sciurus carolinensis) voluntarily visiting the YouTuber's garden cross a parcour to earn a food reward. When 'failing' one of the tasks, the squirrels were catapulted off the track inducing an initially uncontrolled rotation of the body. We preliminary analyzed from the video that firstly the squirrels rotate their tails to stabilize the head to visually fix the landing site. Then, the tail starts to rotate to induce a counter moment to slow down and eventually stop the body rotation preparing the squirrel for the landing. To test the hypothesis that squirrels could utilize tails during mid-air reorientation, and gain insight into tail function essential to the mechanics of this remarkable self-righting behavior, and based on basic spatio-temporal information that we extracted from preliminary observations of Sciurus carolinensis, we use an analytical model to predict squirrel kinematics on unexpected ballistic trajectories. Righting maneuvers are optimized in a multibody model which computes tail trajectories. This model is also used to explore the limits of inertial aerial righting. To further substantiate this model and demonstrate the underlying mechanics, we developed an abstracted squirrel robot completed with an actuated tail to replicate self-righting behavior. The squirrel-inspired physical model uses two high speed brushless motors to create a 2-DoF tail capable of rapid impulsive movements to test mid-air righting in a physical model.

@inproceedings{SICB2021_squirrel,
  title = {Self-righting in squirrels during unexpected falls – towards the crucial function of bushy tails in arboreal mammals},
  author = {Fukushima, Toshihiko and Siddall, Robert and Byrnes, Gregory and Nyakatura, John A. and Toussaint, S\'{e}verine and Ardian, Jusufi},
  journal = {Integrative and Comparative Biology},
  volume = {61},
  number = {Supplement 1},
  pages = {P11-2},
  publisher = {Oxford University Press},
  organization = {Society for Integrative and Comparative Biology},
  month = jan,
  year = {2021},
  doi = {10.1093/icb/icab002},
  url = {https://sicb.org/abstracts/self-righting-in-squirrels-during-unexpected-falls-towards-the-crucial-function-of-bushy-tails-in-arboreal-mammals/},
  month_numeric = {1}
}