The Telltale of Turtles: Visual and Olfactory Cues Raccoons Use to Find Diamondback Terrapin Nests Chris&ne Kasparov, Department of Biology, Hofstra University, Hofstra University, Hempstead, NY Sarah Edmunds, Advanced Inquiry Program at Miami University/Wildlife Conserva&on Society, Bronx, NY Alexandra Kanonik, WildMetro, P.O. Box 4220, Grand Central Sta&on, NY, NY Russell L. Burke, Department of Biology, Hofstra University, Hofstra University, Hempstead, NY
Abstract Nest preda&on by raccoons (Procyon lotor) is the primary cause of mortality of diamondback terrapins (Malaclemys terrapin) in New York’s Jamaica Bay Wildlife Refuge. We replicated the methods of Burke et. al (2005) to test whether a decade of conserva&on efforts had resulted in a change in raccoon preda&on behavior. We created ar&ficial diamondback terrapin nests in the sand and mixed grassland habitats of Ruler’s Bar Hassock during the 2016 nes&ng season. We mimicked the nine types of ar&ficial nest designs as described by Burke et al. and added a new treatment type for further inves&ga&ve purposes, crea&ng at least sixteen nests for each treatment. The various treatments were designed to test the effects of moisture, human scent, terrapin scent, ocean water scent, fresh water scent, soil disturbance, and flag markers on nest preda&on. Ar&ficial nests were monitored for signs of raccoon digging for four days following construc&on, and were considered “depredated” if raccoon digging was noted anywhere between the flags. Suppor&ng Burke et. al’s findings, we found that marking nests with flags did not affect preda&on rates. However, contrary to their findings that human scent decreased preda&on rates, we found that nests with human scent had high preda&on rates, similar to other treatments in which a hole was dug. We conclude that aaer a decade of conserva&on work at this site, raccoons seem to no longer be repelled by human scent, and con&nue to locate nests primarily based on soil disturbance, not visual markers, moisture, or olfactory cues.
Materials and Methods
We mimicked the nine types of ar&ficial nest designs (called “treatments”) as described by Burke et. al (2005) and added a tenth treatment type for further inves&ga&ve purposes: Treatment 1 acted as a control; it was meant to most closely simulate a real terrapin nest flagged at approximately 25 cm at either side of the nest, typical of flagged nests at this site since 1998. Surgical gloves meant to mask human scent were worn while crea&ng approximately 10 cm deep ar&ficial nest holes, and terrapin-scented sand, which was created by placing an adult female terrapin in a container of beach sand for at least 30 min, was mixed with plain sand to fill the holes. The resul&ng surfaces were then smoothed and pahed down, simula&ng the ac&ons of actual terrapins making nests. Treatments 2 and 3 were designed to test if flags placed at varying distances at either end of the nests would influence depreda&on rates, inves&ga&ng if the raccoons were using the flags themselves as visual cues to find nests. Otherwise iden&cal to Treatment 1, Treatment 2 featured flags placed approximately 60 cm to either side of the nest, while Treatment 3 featured flags placed at approximately 100 cm to either side of the nest. Treatment 4 was designed to test if raccoons had come to associate only orange flags with nests, or if they would be ahracted to other colored flags as well. Thus, green flags were implemented, with all other condi&ons remaining the same as with Treatment 1. Treatment 5 acted to test if moisture itself was a cue to the presence of a terrapin nest. This treatment type was constructed iden&cally to Treatment 1, except plain sand was used to fill the hole. Treatment 6 acted to test whether raccoons would dig in the presence of orange flags alone, with no hole digging or other manipula&ons. For this treatment type, the flags were placed approximately 25 cm to either side of an arbitrary, undisturbed spot. Treatment 7 was designed to test the effect of human scent on preda&on rates. This treatment was iden&cal to Treatment 1, with the excep&on that no gloves were worn while digging the hole, and human saliva was mixed with plain sand to fill the hole. Treatments 8 and 9 were designed to test the effec&veness of various scents as cues to nests. These treatments were iden&cal to Treatment 6, with the excep&on of 50 ml of falcon tube-measured ocean water being poured on top of the “nest site” for Treatment 8, and 50 ml of falcon tubemeasured fresh water being poured on top of the “nest site” for Treatment 9. Treatment 10 was designed to test the effect of terrapin scent alone on preda&on rates. For this treatment, the surface of the “nest site” was smoothed if needed, with a gloved hand, and flags were placed approximately 25 cm on either side of an arbitrary spot with no hole-digging, much like for Treatment 6. A falcon tube was used to measure 100 ml of terrapin-scented sand, which was made in the same way as described in Treatment 1, and poured directly on top of the “nest site.” Ar&ficial nests were monitored for signs of raccoon digging for four days following construc&on, and were considered “depredated” if raccoon digging was noted anywhere between the flags (Burke et. al, 2005).
Results and Conclusions
Of real terrapin nests, 67% were depredated this 2016 season. All ar&ficial nest treatments in which a hole was dug (Treatments 1-5, 7) were depredated at rates higher than this background rate (T1= 92%, T2 and T3= 81%, T4=80%, T5= 75%, T7= 88%) . Treatment 1 (N=36), designed to most closely simulate real terrapin nests, had the highest depreda&on rate (92%). Treatments 2 (N=16) and 3 (N=16), with orange flags at varying distances from the hole, and Treatment 4 (N=25), with green flags, were depredated at similarly high rates (81%, 81%, and 80%, respec&vely). Treatment 6, with no hole, moisture, or olfactory cues, had the lowest depreda&on rate (6%). Treatments 8-10, with no hole but various olfactory cues (fresh water, ocean water, and terrapin scent, respec&vely) were depredated at higher rates than Treatment 6, but lower than the background depreda&on rate of real terrapin nests (31%, 38%, and 47%, respec&vely). Suppor&ng Burke et. al’s 2005 findings, we found that marking nests with flags did not affect preda&on rates. However, contrary to their findings that human scent decreased preda&on rates, we found that nests with human scent had high preda&on rates, similar to other treatments in which a hole was dug. Furthermore, the findings of Burke et. al (2005) supported ocean water as a key olfactory cue, but our results showed comparably low preda&on rates between both ocean water (8) and fresh water (9) treatments when compared to the control. We conclude that aaer a decade of conserva&on work at this site, raccoons seem to no longer be repelled by human scent, and con&nue to use soil disturbance as a primary indicator of nests, rather than visual markers, moisture, or olfactory cues.
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