Fossorial amphibians spend up to ten months belowground, but research into this critical habitat has been impeded by a lack of noninvasive detection methods. Ground-penetrating radar (GPR), however, offers a promising tool because amphibians have theoretically strong electromagnetic (EM) contrasts relative to the soil matrix, and thus potentially high detectability. The objectives of this study were to (1) evaluate GPR by (2) experimentally-inducing three soil thermal regimes that promote stratification in the burrowing depths of 15 Eastern American Toads (Anaxyrus americanus americanus) during the winter of 2011–2012 in Madison, WI, USA. We calculated reflectability and established the unique electronic signature of the toads in GPR datasets through measuring the water contents of the soil and toads as a proxy for the relative dielectric constant, an EM metric in GPR assessment. As toads emerged in the spring of 2012, we verified the GPR imagery with their emergence locations. The contrast in relative dielectric constants between the toads and the soil provided reflectance ratings that were 12–24 times greater than the detectable limit and confirmed that the toads were distinguishable from other soil features. The winter mortality of the toads, however, was 73%, which limited the replication with which GPR could be evaluated. We attribute the depth and rate of frost penetration from the treatments and weather of 2012 as the probable cause of mortality. Future research and conservation efforts may be facilitated with GPR by tracking temperate species belowground and linking behavior to environmental stressors.
Stock, Melanie N., Hart, David J., and Balster, Nicholas J. "Detecting Soil Macrofauna Using Ground-Penetrating Radar." 2019.