Meeting Abstract
Many arboreal animals traveling through the canopy are challenged to stably walk or run, and then to leap from compliant branches to cross gaps and land on a target. As animals traverse further from the trunk, compliance increases while the gap size to be crossed decreases. We’ve previously shown that both greater compliance and larger gaps increase the difficulty of targeted leaping. Therefore, a tradeoff is presented between the length of the gap that must be crossed and the compliance of the substrate at any chosen takeoff point. We created an outdoor arena with interchangeable compliant rods and a small landing perch. We trained free-ranging fox squirrels (Sciurus niger) to run and leap across a gap using rods of equal diameter but with low, medium or high compliance. Rods were cantilevered 90 cm across a 100 cm gap. Beam compliance increased to the third power along the length of the rod. Vertical displacements at the 50% along the rod due to body weight were 1.6, 5.0 and 23.9 cm for the low, medium and high compliance rods, respectively. Squirrel traversal behavior was affected by rod compliance. On the least compliant rod, they leaped from a full range of points or walked onto the landing perch. On greater compliance rods, they elected to leap earlier – across longer gaps. When walking or running across the rod, squirrels splayed their toes prior to each footfall, leaped with one hind limb in front of the other, creating asymmetry during launch, and then brought their feet in alignment with the landing perch for contact using contralateral symmetry, first fore-limbs then hind-limbs. Our next step is to investigate the squirrels’ mechanisms of compliance estimation and the possible role of learning in deciding when to leap.
