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Sinkholes as a Source of Wildlife Mortality
Nathan W. Klopmeier, Sarah M. Pesi, Gail Morris, and Mike Conner

Southeastern Naturalist, Volume 17, Issue 4 (2018): N64–N67

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2018 Southeastern Naturalist Notes Vol. 17, No. 4 N64 N.W. Klopmeier, S.M. Pesi, G. Morris, and M. Conner Sinkholes as a Source of Wildlife Mortality Nathan W. Klopmeier1, Sarah M. Pesi1, Gail Morris1,*, and Mike Conner1 Abstract - Sinkholes are common in karst terrain, and their impacts on wildlife are not well documented. At the Joseph W. Jones Ecological Research Center in southwestern Georgia, we observed 3 separate incidents of wildlife being negatively impacted by entrapment within a single sinkhole. Sinkholes are a common feature of karst terrain, which is characterized by water-soluble bedrock such as limestone (Beck and Arden 1984, Kuniansky et al. 2016). The initial formation of a sinkhole occurs gradually, as water dissolves subsurface rock. The final step can occur suddenly when the surface collapses (Beck and Arden 1984) creating the sinkhole. Changes in groundwater can accelerate the formation process (Gordon 2011). Groundwater provides buoyant support when sediments are submerged (Gutiérrez et al 2013). When groundwater levels decrease, this buoyant support is lost, which increases the effective weight of the sediment, and may result in surface collapse (Sinclair 1982). Additionally, greater water input, through rainfall or irrigation, increases the rate of dissolution (Gutiérrez et al 2013). Heavy rainfall, especially following a period of drought, often triggers the opening of sinkholes (Hyatt and Jacobs 1996). The Joseph W. Jones Ecological Research Center at Ichauway (hereafter, Ichauway) in Baker County is located on the Dougherty Plain of southwestern Georgia. The Dougherty Plain is a region of karst terrain underlain by over 1000 m of limestone, making it susceptible to sinkholes (Beck and Arden 1984). Several sinkholes are known to exist on Ichauway, including one that was discovered on 13 March 2013 in an active research area. The opening may have been triggered by rainfall of 3.1 cm on 11 March. There were several additional bouts of heavy rainfall in the month prior to the sinkhole collapse that likely aided in its formation. Total rainfall over February of 2013 was 38.4 cm (mean ± SE February rainfall on Ichauway from 2000 through 2017, according to an on-site weather station, was 11.7 ± 1.9 cm). This sinkhole was ~4.5–5.0 m deep and ~2.0–2.5 m wide. The sinkhole had an overhang encompassing the entire circumference of the opening (Fig. 1). Since the formation of this sinkhole, researchers opportunistically checked it when working nearby and observed 3 incidents of wildlife becoming entrapped. In the first case of wildlife entrapment, 2 dead Sigmodon hispidus Say & Ord (Hispid Cotton Rat) were found at the bottom of the sinkhole on the same day that it was discovered (Fig. 2). It is unknown if the Hispid Cotton Rats fell into the open hole or became entrapped when the surface collapsed. After the sinkhole was discovered, a woven wire fence was constructed around the perimeter, to alert humans to the presence of the sinkhole. The fence was 1 m tall and made of metal posts and wire weave varying from 9 x 8 cm at the bottom to 18 x 8 cm at the top. The second incident occurred on 18 June 2014, after fence construction, when a Sylvilagus floridanus (J.A. Allen) (Eastern Cottontail) was found inside the sinkhole. Two juvenile Lynx rufus (Schreber) (Bobcat) were discovered inside the sinkhole on 31 October 2017 (Fig. 2). Upon returning to the sinkhole, we observed that one of the Bobcats was dead. A Browning 2016 Recon Force Platinum trail camera (Browning, Morgan, UT) was placed to document events until we could provide a means to allow the remaining Bobcat to escape. Our camera captured an adult Bobcat pacing the perimeter of the sinkhole. The Bobcats 1Joseph W. Jones Ecological Research Center, 3988 Jones Center Drive, Newton, GA 39870. *Corresponding author - Manuscript Editor: Marcus Lashley Notes of the Southeastern Naturalist, Issue 17/4, 2018 N65 2018 Southeastern Naturalist Notes Vol. 17, No. 4 N.W. Klopmeier, S.M. Pesi, G. Morris, and M. Conner can be heard calling to one another on the videos (a video showing this interaction can be viewed here: Physically retrieving the Bobcat was not attempted due to potential risk of further collapse of the sinkhole. Therefore, we placed boards and a sapling inside the sinkhole to Figure 1. Sinkhole which was discovered at the J. W Jones Ecological Research Center at Ichauway in Baker County, GA, on 13 March 2013. Figure 2. Dead Sigmodon hispidus (Hispid Cotton Rat) found inside sinkhole at the J.W. Jones Ecological Research Center at Ichauway in Baker County, GA, on 13 March 2013 (left). Two juvenile Lynx rufus (Bobcat) found inside the sinkhole (right) on 31 October 2017. 2018 Southeastern Naturalist Notes Vol. 17, No. 4 N66 N.W. Klopmeier, S.M. Pesi, G. Morris, and M. Conner provide a means for the Bobcat to escape. On 4 November, we discovered that the Bobcat was no longer present, and we assumed it escaped. The impact of sinkholes on the landscape and human population has been well documented, e.g., causing damage to roads and buildings (Dougherty and Perlow 1988, Hermosilla 2012), draining streams and lakes (Jovanelly 2014), conducting contaminants into aquafers (Lindsey et al. 2010), and causing loss of human life (Hermosilla 2012). The creation of microhabitats in the form of pools and mesic depressions has also been studied (Francl et al. 2010, Keiller 2011). However, our observations indicate sinkholes also cause wildlife mortalities, which to our knowledge has not previously been documented in scientific literature. News articles have described the rescue of animals such as deer, Canis latrans Say (Coyote), Phascolarctos cinereus Goldfuss (Koala), Canis lupus familiaris L. (Domestic Dog), Bos taurus L. (Cattle), and Equus ferus caballus L. (Horse) from sinkholes that would have been otherwise unable to escape (BBC 2017, Gould 2017, Kilen 2014, KOMO News 2017, Miller 2009, Witt 2017). We documented entrapment of 3 additional wildlife species, despite the presence of a fence, which likely deterred animals, and the fact that research at this site ended in early 2015, significantly reducing opportunities to detect animals which may have fallen into the sinkhole. As a result, additional entrapments were potentially much greater than observed. Sinkholes exist in a variety of shapes and depths, not of all which are likely to cause the entrapment and eventual mortality of wildlife. In particular, steep sides and greater depth create conditions from which it is hard for wildlife to escape. Deep, steep-sided sinkholes, such as the one described here, will eventually erode to create gentler slopes (Beck and Arden 1984) and likely reduce the risk of wildlife mortality. Climate-change projections for the Southeast favor increased frequency of sinkhole formation; periods of drought are expected to increase, with rainfall occurring in more intense events (Karl et al 2009). These conditions should contribute to more frequent surface collapse of sinkholes. For example, in 1994 Tropical Storm Alberto resulted in the creation of more than 300 sinkholes around Albany, GA (Hyatt and Jacobs 1996). Human activities can also contribute to and accelerate the process of sinkhole formation. Groundwater withdrawal for irrigation and human consumption can cause the groundwater levels to drop, which creates conditions conducive to sinkhole collapse (Aurit et al 2013, Gutiérrez et al 2013). With an increasing human population in the Southeast, the associated increase in groundwater withdrawal may also contribute to more frequent sinkhole formation. With current precipitation trends and increasing demands on groundwater creating conditions more favorable to creation of sinkholes, the probability of sinkholes forming may increase, which could make wildlife entrapment and mortality a more frequent occurrence in the future. Acknowledgments. We would like to thank the Joseph W. Jones Ecological Research Center for funding and support, Daniel Knapp for providing us with early information about the sinkhole, and Stribling Stuber for assistance with our geological literature review. We thank 2 anonymous reviewers and the editor for suggestions which improved this manuscript. N.W. Klopmeier and S.M. Pesi contributed equally to this work. Literature Cited Aurit, M.D., R.O. Peterson, and J.I. Blanford. 2013. 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Relations between sinkhole density and anthropogenic contaminants in selected carbonate aquifers in the eastern United States. Environmental Earth Sciences 60:1073-1090. Miller, A.L. 2009. A young, worn-out Coyote was rescued Thursday afternoon from a sinkhole off Southwest 27th Avenue. Ocala Star Banner. Available online at LK/20090917/news/604232097/OS/. Accessed 8 May 2018. Sinclair, W.C. 1982. Sinkhole development resulting from ground-water withdrawal in the Tampa Area, Florida. Water Resources Investigation Report 81-50. US. Geological Survey, Reston, VA. Pp. 8–17. Witt, G. 2017. Park officials rescue deer from sinkhole in Cades Cove. USA Today Network. Available online at smoky-mountains-national-park/98050056/. Accessed 12 December 2017.