As is true for many North American turtles, nest predation by Raccoons (Procyon lotor) is the primary cause of mortality of Diamondback Terrapin (Malaclemys terrapin) eggs laid at Jamaica Bay, New York. Nearly 100% of terrapin nests laid are predated in some years. In addition to natural cues left by terrapins, conservation practices since 1998 have included marking terrapin nests with conspicuous vinyl flags, potentially adding an artificial cue. After initial experiments in 2003 & 2004, in 2016 & 2017 we again used artificial nests to test whether more than a decade of subsequent field work at the same site resulted in a change in raccoon behavior. We replicated the previous experiments by constructing the same nine artificial nest treatments and adding four new treatments. We also investigated the effect of soil disturbance itself using geosmin, a pungent, organic compound produced by Actinobacteria. We further tested whether detection of natural cues was affected by rainfall, using both artificial and natural terrapin nests.
Results/Conclusions
Our initial research using artificial nests at this site indicated that marking nests with flags did not increase predation rates, that raccoons located nests based on soil disturbance and ocean water scent, and raccoons were repelled by human scent. Currently, flag markers are still not important cues for raccoons locating terrapin nests, but ocean water scent no longer increases raccoon predation, and human scent no longer repels raccoons. Geosmin increased predation rates. We found that predation rates on natural and artificial nests were inversely correlated with the amount of rain on the day nests were laid/constructed, and heavy rainfall the evening after a nest is laid can dramatically reduce predation rates. These results indicate that raccoons in Jamaica Bay continue to locate nests primarily by relying on the tactile cue of soil disturbance rather than visual markers, moisture, or olfactory cues, and that selection may favor turtles that nest soon before heavy rainfall, which mask those cues.