Semi-aquatic turtles are important parts of aquatic ecosystems, and tend to be favorably viewed by the public. Urban areas, however, pose considerable threats to semi-aquatic turtle populations. Urbanization represents the primary cause of species endangerment for turtles (Czech et al. 2000), and semi-aquatic species in particular face increased pressures because they utilize both terrestrial and aquatic environments (Marchand and Litvaitis 2004; Gibbs and Steen 2005). In order to maintain viable populations of turtles in urban environments, adequate juvenile recruitment and high adult survivorship are necessary.
Our focus on multiple species (see “Common Species”) - such as painted turtles, snapping turtles, and mud turtles - with divergent life-histories and habitat requirements, provides us with information directly applicable to other critically endangered species of the eastern United States, such as spotted turtles and Blanding’s turtles. In a previous study conducted by researchers in the Davidson College Herpetology Lab, annual survivorship estimates for painted turtles were 60% for males and 80% for females. For mud turtles, survivorship was estimated at 57% for males and 74% for females (Eskew et al.2010). These values are considerably less than those necessary to maintain long-term viability in semi-aquatic turtle populations (Congdon et al. 1993).
“The previously successful survival adaptations of turtles, including delayed sexual maturity, high juvenile mortality, and a long adult life-span with low natural mortality, have left turtle populations vulnerable to new, potentially devastating threats posed by human exploitation and development-related pressures.” – Global Action Plan for Conservation of Tortoises and Freshwater Turtles
Urban areas tend to have high levels of wetland degradation and destruction. In North Carolina, for example, approximately 50% of wetlands have been reduced since pre-settlement times due to development and agricultural practices (Mitch and Gosselink 1993). Remaining wetlands tend to be highly isolated from neighboring wetlands due to barriers associated with development such as roads.
Dual Habitat Requirements
While the aquatic habitat offers resources for foraging and other activities, all semi-aquatic species in the United States require terrestrial habitat for nesting. The terrestrial environment is used both for travel to the nesting site and the construction of the nest itself (Bowne et al. 2006). In the case of some species such as mud turtles, upland habitat is critical for overwintering sites (Harden and Dorcas 2009). The quality of aquatic and terrestrial habitats and ability for successful movement through the terrestrial environment are directly linked to the juvenile recruitment and adult survivorship necessary for maintaining viable population size (Rizkalla and Swihart 2006; Bowne et al. 2006; Gibbons 1987; Congdon et al. 1993).
Landscape degradation, high levels of road mortality, and nest predation due to human-subsidized predators all contribute to low survivorship and recruitment rates of semi-aquatic turtles in urban areas (Eskew et al. 2010; Marchand and Litvaitis 2004). Long-term viability of populations in urban regions, therefore, tends to be low.
The Role of Golf Courses
Golf courses generally include numerous aquatic and terrestrial habitats suitable for turtles that constitute high percentages of overall land cover. Various species of semi-aquatic fauna, such as amphibians (Scott et al. 2008) and birds (Gillihan 1999), utilize golf course habitats in addition to semi-aquatic turtle species (Colding et al. 2009). In some urbanized areas, golf courses may represent the best available habitat for these tutles. Based on previous research in the DCHL, turtle populations on golf courses likely suffer from low recruitment and survivorship which may result in the demise of the species population (Eskew et al. 2010). Further research is necessary to document the abundance of turtles inhabiting golf course ponds and methods for management to best achieve conservation of the resident species.
The goals of our project included:
It is our hope that golf course managers in the southeastern United States will take our suggestions into consideration in planning design and maintenance of their courses and be able to utilize the resources and recommendations provided herein.
Click here to view a PowerPoint presentation (PDF file) about turtle population densities by pond type and pond area by Lynea Witczak and Courun Williams.
Click here to view a PowerPoint presentation (PDF file) about nest-site selection and depredation by Shawna Foley.
Davidson College Herpetology Lab