High-resolution geophysical imaging of reptile burrows (San Salvador rock iguana, the Bahamas): implications for ichnology and conservation ecology

Abstract

Neoichnological research of terrestrial tracemakers in coastal settings provides important palaeoenvironmental information about their context within the subaerial facies. Here we present the first geophysical dataset of reptile burrows in a carbonate substrate and use it to help visualize parts of the burrows of the Bahamian (San Salvador) rock iguana (Cyclura rileyi). High-resolution 800 MHz ground-penetrating radar (GPR) images within an enclosure on San Salvador Island were employed to discriminate between the electromagnetic signal response from subsurface anomalies related to air-dominated voids or live animals within burrows. The dielectric contrast between the carbonate substrate and open burrows was sufficient to identify the majority of the 15–20 cm-wide subsurface extensions of the inclined tunnels in the upper 30–40 cm. Whereas limestone clasts induced some interference, it is possible to differentiate their high-amplitude diffractions from those produced by the iguana burrows. Our research indicates that GPR imaging is a viable, rapid, non-invasive method of visualizing animal burrows, with implications for neoichnology, palaeoichnology, and conservation ecology of semi-fossorial species. Furthermore, the critically endangered status of Bahamian land iguanas, as well as ongoing threats from natural and introduced pressures, highlights the need for research into their ichnological record.