The Effects of Burrow Collapse on the Gopher Tortoise (Gopherus polyphemus)

Abstract

The gopher tortoise (Gopherus polyphemus) is a species in decline due, in part, to loss of habitat and altered land use. One particular area of concern is the use of vehicles during urbanization and agriculture practices that may collapse their burrows, entombing the tortoise and potentially causing it harm. Few studies have examined the consequences of burrow collapse and entombment on gopher tortoises. We collapsed 42 burrows using logging and military vehicles in 2003 and 2004 at several sites on Fort Benning in southwest Georgia. We measured the extent of collapse, documented the amount of time it took each tortoise to self-excavate, and determined the distance from the original burrow opening to the excavation exit hole. After the tortoises self-excavated, we tracked their movements to determine burrow usage patterns and compared this to what was observed pre-collapse. We returned in 2005 to again track movements of the experimental tortoises as well as a group of control tortoises that were captured. In our study, 41 of 42 tortoises self-excavated, although there was considerable variation in the time to self-excavation (several hours to 85 days). Physical factors that appeared to adversely affect the time until self-excavation were soil type and precipitation prior to the collapse. We also observed a far higher rate of burrow abandonment by tortoises that self excavated than has previously been documented for un-manipulated tortoises. Although none of the entombed tortoises were harmed during our study (including the one that did not self-excavate) and there was no changes in movement behavior, some of them were entombed during a time of year when mating occurs. This lost mating opportunity, the negative impact of soil type and precipitation on excavation times, in addition to the high rate of burrow abandonment, suggests that the process of burrow collapse and entombment may negatively impact this declining species.