Digging Biomechanics in Geomyoid Rodents

Subterranean digging behaviors provide opportunities for protection, access to prey, and predator avoidance for a diverse array of vertebrates, yet studies of the biomechanics of burrowing have been limited by the technical challenges of measuring kinetics and kinematics of animals moving within a substrate. Prior studies of burrowing have recorded a single axis of x-ray video and/or force. However, empirical observations show that burrowing is not restricted to a single axis or plane. I describe a new system called a ‘tunnel-tube’ for measuring 3D reaction force during burrowing. This tunnel-tube has two separate tubes, one ‘entry tube’ that has no soil and a ‘digging tube’ packed with soil. The two tubes are mounted in series with each supported by a commercial 3-axis force transducer. Fourier analysis of forces measured by the tunnel-tube extracts force amplitude as a function of frequency to quantify oscillatory digging forces. The tunnel-tube is used here to quantify scratch-digging forces in three closely-related rodents, pocket gophers, kangaroo rats, and pocket mice. Kangaroo rats produced remarkably high force at high frequencies, suggesting they may be more specialized for digging than previously thought. Pocket gophers and pocket mice both used chisel-tooth digging to dig in harder substrates, indicating that there may be a soil-compaction strength at which the animals transition from scratch-digging to chisel-tooth digging