Herpetology Notes, volume 14: 1067-1072 (2021) (published online on 09 August 2021) Predation on nests of the European pond turtle (Emys orbicularis): remarks from failed field experiments Enikő Horváth1, Peter Kaňuch1,2, and Marcel Uhrin1,* Abstract. The viability of many turtle species, including the European pond turtle (Emys orbicularis), is imperilled by nest depredation. Depredation rates of the E. orbicularis population in eastern Slovakia are high; therefore, we aimed to identify nest predators and to determine which sensory cues they use to find the nests. From the set of different experimental trials with artificial nests in the field, only the application of turtle-scented water imitating the female migration path to the nesting site suggested potential predation of turtle nests driven by olfactory cues. Although we did not observe depredation of the installed artificial nests, we identified badgers (Meles meles), wildcats (Felis silvestris), and wild boars (Sus scrofa) as potential predators. Our results also imply that the use of chemical repellents should be considered for nest protection of the study species in Tajba National Nature Reserve. Key words. Nest depredation, artificial nests, nest cues, conservation, Slovakia Introduction Populations of the European pond turtle (Emys orbicularis) are mostly decreasing and considered Nest predation in chelonians is one of the leading endangered mainly due to habitat fragmentation and causes of mortality during their egg stage. The rate of nest isolation (Rogner, 2009). The species represents the depredation is generally high, and it negatively affects only autochthonous turtle species in Slovakia, with the viability of local populations (Stanford et al., 2020). two known reproducing populations in the eastern and Nest depredation can be influenced by multiple ecological western parts of the country (Jablonski et al., 2015). factors, including nest distance from the water habitat, Among other threats, the long-term studied population rainfall, as well as vegetation cover (Kolbe and Janzen, in Tajba (eastern Slovakia; Novotný et al., 2004, 2008; 2002; Dawson et al., 2014; Czaja et al., 2018). Signals Horváth et al., 2017, 2021) is facing high nest depredation used by predators to locate turtles’ nests may be species- rates. Altogether, more than 234 depredated nests were dependent (e.g., Strickland et al., 2010; Buzuleciu et al., recorded during 2011–2017 (Havaš et al., 2018). Racoons 2016), whereas most of the depredation events occur (Procyon lotor), badgers (Meles meles), red foxes (Vulpes within a week after oviposition, likely because cues left vulpes), and wild boars (Sus scrofa) are the most common behind by the nesting female are the most detectable during predators of pond turtle nests in the western part of the this time (Burke et al., 2005; Holcomb and Carr, 2013). species’ range (Zuffi, 2000; Schneeweiß and Breu, 2013); However, depredated nests can be observed throughout the latter three mammal species also commonly occur in the whole incubation period (Riley and Litzgus, 2014). eastern Slovakia (Krištofík and Danko, 2012). Thus, it Therefore, to protect chelonian populations from nest is crucial to understand the behaviour of nest predators predation, various predator-exclusion approaches have with the aim of improving the effectiveness of protective been used in conservation actions (Buhlmann and Osborn, management activities. Therefore, the goals of our study 2011; Riley and Litzgus, 2013; Schindler et al., 2017). were to identify the predators of E. orbicularis nests and to determine which sensory cues they use to find the turtles’ nests. For this reason, we examined the effect of 1 Department of Zoology, Institute of Biology and Ecology, different artificial nest settings on the activity of potential Faculty of Science, P.J. Šafárik University, Šrobárova 2, 041 nest predators. 80 Košice, Slovakia. 2 Institute of Forest Ecology, Slovak Academy of Sciences, Ľ. Materials and Methods Štúra 2, 960 53 Zvolen, Slovakia. * Corresponding author. E-mail: [email protected] General experimental design. At three sites in eastern © 2021 by Herpetology Notes. Open Access by CC BY-NC-ND 4.0. Slovakia, we constructed artificial nests by hand-digging 1068 Enikő Horváth et al. ~10–12 cm deep holes, a depth similar to natural E. at a distance of 2 m from the two nests, situated ~1.5 orbicularis nests (Novotný et al., 2004). During the m from each other, and arranged with the camera in a construction, we wore surgical gloves and clean rubber triangle (Fig. 1A). Nest sets were filled by two different boots to minimise the contamination of the construction substances that should stimulate interest of potential site by human scent. All equipment used was placed predators. One of the nests contained turtle-scented sand, on a clean plastic sheet spread out on the ground, and water from the Tajba oxbow, and a chicken egg. We we did not kneel on the ground while digging. We placed the chicken egg into the excavated hole and refilled designed three experiments with different combinations the hole with turtle-scented sand mixed with water from of settings (Table 1), and all of them were monitored the Tajba marsh. Additionally, we applied water to the by wildlife cameras (Spromise S308 940nm) to record top of the artificial nests (~60 ml) using a sterile syringe. predator species and the frequency of their occurrence. Water from the Tajba oxbow was obtained on the day of Cameras were set to rapid-fire (five photos after every the nest construction using a clean glass. To obtain turtle- detected stimulus) at various heights and distances from scented sand, we placed adult turtles into a box filled with the artificial nests, depending on the experimental design sand from the nesting site for 24 h. Because we did not (see below; Fig. 1). All artificial nests were monitored have access to E. orbicularis individuals at that time, we for three consecutive days after construction since nearly replaced them by two privately kept adult Trachemys all predation events on E. orbicularis nests occur on the sp. The other artificial nest contained the excavated soil same day of oviposition or on the following day (Najbar from the nest hole mixed with human urine (~60 ml) as and Szuszkiewicz, 2005; Havaš and Danko, 2009). an olfactory stimulus. Cameras were checked only at the end of the experimental Experiment 2. Artificial nest sets organised in the field period to avoid any intermittent disturbance of the area. in the same way as in Experiment 1 were constructed near We declared artificial nests as depredated if any sign of another frequently used nesting site (Tajba; 48.367°N, digging was visible. Different experimental trials were 21.767°E). Nests were filled by two different but variant conducted in April, June, and November 2020. stimuli at both sites. Ten nest holes were filled with Experiment 1. Ten artificial nest pairs (i.e., a total of turtle-scented sand only, and ten nest holes were filled 20 nests) were constructed near Tajba National Nature with chicken eggs only. To obtain turtle-scented sand, Reserve, Slovakia (ca. 48.367°N, 21.783°E), on the six adult Emys orbicularis (one male, five females) were edge of the most frequently used nesting site in the area isolated for 72 h at ZOO Košice in a terrarium filled with (Novotný et al., 2004). Nest pairs were randomly placed sand from the nesting site. After 72 h, the sand was used at a distance of at least 5 m from each other and monitored for the construction of the artificial nests. by one wildlife camera each. The cameras were mounted Experiment 3. Ten randomly placed artificial nests ~1.2 m above the ground on trees or vineyard poles, were constructed near the village of Poľany (48.450°N, Table 1. List of experiments showing the different designs. Tajba is an area of permanent turtle nesting activity, whereas in Poľany nesting activity is observed only occasionally. Experiment Artificial Nest Content n Site Dates nest hole filled with turtle-scented 1 10 sand + chicken egg Tajba 9–12 April 2020 nest hole filled with human urine 10 nest hole filled with turtle-scented 2 10 sand from ZOO Tajba 11–15 June 2020 nest hole containing chicken egg 10 disturbed soil with turtle-scented 3 water on the top + 10 m long turtle 10 Poľany 19–21 November 2020 scented trail Studies on Emys orbicularis Nest Predation 1069 Figure 1. Arrangements of the artificial nest sets (indicated by the clutch of eggs) and camera traps in Experiments 1 and 2 (A) and Experiment 3 (B). 21.967°E), where the last nesting activity of E. Results orbicularis was observed in 2018. This local population Over 3000 images were analysed during the study. In is probably now extinct, as the turtles’ water habitat has Experiments 1 and 2 no predators found the artificial been dried out since 2015 (Havaš et al., 2018). In this nests. In Experiment 1, besides the presence of some experiment, nests were simulated as disturbed soil with roe deer (Capreolus capreolus) and European hares turtle-scented water on the top of the nests to imitate (Lepus europaeus), an American mink (Neovison vison) the odour of bladder water leaked by female turtles probably crossed the monitored area, but none of the during the excavation of the nest hole (Rogner, 2009). In artificial nests were destroyed and all remained intact. addition, to simulate the path of the turtles to the nesting In Experiment 2, no predators were recorded by the site, a 10-m-long artificial trail was sprayed from each installed cameras, and only some roe deer and European nest using the same turtle-scented water (Fig. 1B). The hares crossed the cameras near the E. orbicularis nesting turtle-scented water originated from a 20-l tank, where site.