A Test of Substrate Sweeping as a Strategy to Reduce Raccoon Predation of Freshwater Turtle Nests, with Insights from Supplemental Artificial Nests

Visible sign produced by nesting turtles has been suggested to be a cue used by foraging raccoons (Procyon lotor) to locate nests. Experiments investigating the potential for reducing turtle nest predation by eliminating these surface markings by broom sweeping nesting areas were conducted at 2 Graptemys nesting sites along the lower Wisconsin River in Iowa County, Wisconsin, during 2013 and 2014. Ninety-five percent of the natural nests in unswept control areas (n = 20) and all of the nests in swept treatment areas (n = 16) were depredated by raccoons within 24 hrs. Supplemental artificial nests with refilled manufactured cavities but lacking potential olfactory turtle-or egg-related cues were also excavated by raccoons within similar time lines (97% within 24 hrs) and at high rates both when unswept (100%, n = 20) and when swept (95%, n = 19). However, artificial facsimiles of the surface markings left by nesting turtles, lacking cavities, were disturbed less frequently (26%, n = 19). Findings suggest that broom sweeping was ineffective because the location cues used by raccoons to find newly constructed nests are not primarily visual but olfactory and related to soil profile disturbance, possibly via the microbial metabolite geosmin.