BIG BURROWS OF ALLIGATORS CHANGE ECOSYSTEMS, HELP ALLIGATORS SURVIVE COLD WINTERS, DROUGHTS, AND FIRES, AND ALLOW THEM TO BE TERRESTRIAL PREDATORS

American alligators (Alligator mississippiensis) are well known as apex predators in fresh-water and marginal-marine ecosystems of the southeastern U.S. However, alligators are less appreciated for their role as ecosystem engineers, in which they modify environments via their traces: small ponds, trails, and burrows (dens). Alligator dens are especially important traces, serving many purposes. These burrows are often used as nurseries for hatchling alligators accompanied by their mothers, but also mollify the deleterious effects of cold winters, droughts, and fires on alligators of all ages. Nonetheless, few researchers have described alligator dens ichnologically or explored the ecological dimensions of these traces. To address these points, we studied alligator dens on St. Catherines Island (Georgia), a sparsely developed island with little human influence. We used a combination of ArcGIS and LiDAR maps to study the spatial distribution of dens on the island. Where practical, we measured widths and heights of den entrances, recorded whether dens were occupied by alligators or not, and noted prey remains near den entrances. Ground-penetrating radar (GPR) was applied to render den interiors, which are poorly known because of researcher safety concerns. Dens are ichnologically distinct, identifiable as half-moon cross sections that range from 25 cm to >1 m meter wide at their entrances; these openings connect to downward-sloping tunnels and turn-around chambers. Old, collapsed dens in a secondary-succession maritime forest gave more information about subsurface forms of these structures, which are 3-4.5 m long and 1-1.5 m wide. Surprisingly, alligators will inhabit dens in maritime forests, well away from any water bodies. In these instances, tunnels intersect the water table, providing underground “wetlands” for their occupants. Raccoon, deer, and vulture remains near entrances of these dens suggest that alligators can become facultative terrestrial predators, ambushing prey that approach their homes. Our spatial analysis also led to a predictive model in which we were able to find abandoned dens in former wetlands ecologically succeeded by maritime forest. In our future research we hope to use photogrammetry and other digital imaging methods to better characterize den interiors as traces.