ANALYSIS OF SUBSURFACE (800 MHZ GPR) IMAGES OF CRITICALLY ENDANGERED SAN SALVADOR ROCK IGUANAS IN BURROWS, THE BAHAMAS

Active bioturbation at several sites with different substrates on the GRC campus provides an opportunity to assess the viability of ground-penetrating radar (GPR) to discriminate between the electromagnetic signal response to biogenic structures and that of associated man-made features. A series of 800 MHz georadar profiles were collected in the exhibit containing several adults of the critically endangered Bahamian (San Salvador) rock iguana (Cyclura rileyi). To minimize disturbance, subsurface images were obtained during morning hours when animals were still in their burrows. The survey design maximized the number of burrow traverses by an integrated grid and circumference layout within an oval enclosure. The dielectric contrast between the carbonate substrate and air-filled burrows was sufficient to identify the majority of 10-15-cm-wide subsurface extensions of the inclined tunnels. Whereas numerous limestone clasts induced interference, it is possible to differentiate their high-amplitude diffractions from those produced by the iguana burrows. At several locations, regularly spaced, inclined reflections at 20-30 cm depth represent cross-bedded lithified aeolianite underlying the burrowed substrate. Signal velocity analysis has the potential of identifying live iguanas within their burrows. Whereas the identification of desiccated animal skeletons in burrows will be difficult due to minimal dielectric contrast, our findings demonstrate the potential of GPR to aid in conservation of these endangered species and to expand our knowledge of the neoichnology of their burrows. Differentiation between burrows and subsurface extensions of cemented stonewalls has implications for evaluating the potential for undermining of engineered structures. Geophysical imaging becomes especially important when abandoned burrows are filled and spoil piles are absent. In addition, this research may aid in identification of infilled burrows associated with the natural exposures of lithified limestone throughout the Bahamas.