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January 3 - Febuary 28, 2021

Meeting Abstract

73-6  Sat Jan 2  Effect of motivation on sequential jump strategy in fox squirrels Wang, LK*; Ruopp, R; Hunt, N; Nguyen, A; Full, RJ; Univ. of California, Berkeley; Univ. of California, Berkeley; Univ. of Nebraska, Omaha; Univ. of California, Berkeley; Univ. of California, Berkeley

Fox squirrels perform incredibly agile feats of saltatorial locomotion. Parameters that squirrels use to make biomechanical decisions when negotiating challenging, complex arboreal terrain remain uncertain. We tested the hypothesis that jump strategy depends on trade-offs of motivation versus falling risk. We trained six free-ranging fox squirrels to leap between three horizontal rods perpendicular to the path of motion at a 1.5m height with modifiable gaps of 0.50m, 0.75m, or 1.00m. We recorded 329 trials for 3D kinematics using 12 high-speed cameras. We observed two distinct jumping strategies: rapid, continuous jumps where squirrels did not stop on the center rod versus slow, discontinuous jumps with pauses on the center rod before conducting the second jump. We tested the hypothesis that discontinuous jumps with a low failure rate would be favored if the reward (peanut) outweighed the perceived risk of pausing. Squirrels only chose continuous escape jumps because they perceived a greater risk of pausing. Rapid, continuous jumps with a higher failure probability were only made at 0.50m and 0.75m increments. During rapid jumps at 0.75m, squirrels had a 10% greater mid-jump spine bending angle. They landed on the middle rod with a 35% larger landing angle, allowing for a rapid transfer of momentum into horizontal velocity during the second jump. While squirrels were quite adept at jumping, their risk of missing the rod with their hind legs increased significantly from 3% to 41% when we increased distances to 1.00m. Squirrels never entirely missed rods, but would often only grasp with their front feet. Squirrels’ cognitive decisions that include motivation and risk play a critical role in determining their biomechanical jump strategy.