Wood Turtle (Glyptemys insculpta) nest protection reduces depredation and increases success, but annual variation influences its effectiveness

Abstract

Habitat loss is the leading cause of species extinctions and is especially detrimental to habitat specialists. Freshwater turtles require specific habitat types at different points in their life cycle; notably, the loss of nesting habitat has led to increased nest depredation and adult mortality. In response, conservationists have implemented nest protection and habitat restoration programs to recover declining populations. While assumed to increase nest survival, effectiveness of these methods has not been rigorously quantified. We located wood turtle (Glyptemys insculpta Le Conte, 1830) nests in Wisconsin and conducted two analyses–logistic regression and logistic exposure–to investigate the influence of management actions and environmental factors on nest survival. The depredation rate decreased by 47% for protected nests and declined as nests aged; the success rate increased by 28% for protected nests and increased for nests in areas with fewer roads. We found high annual variation in success and although weather variables were not predictive, likely due to their coarse-scale, we posit that this inter-annual variation was driven by variation in weather conditions. Our results suggest that nest protection is effective at increasing nest survival, but future efforts should span multiple years to account for the effects of annual variation in environmental conditions.

Not all management is equal: a comparison of methods to increase wood turtle population viability

“…We surveyed for wood turtle nests at known nesting locations at sites A and C in spring 2018 (Bougie et al 2020). We checked nests at least once every 2 weeks from deposition until mid-August, when we installed hatchling cages made from 1.27 × 1.27-cm wire mesh over the center of the nest to trap hatchlings upon emergence.…”

“…Wood turtle populations in Wisconsin are threatened but relatively understudied with no published long-term demographic studies. Researchers have recently quantified vital rates including adult survival (Lapin et al 2019) and nest success (Bougie et al 2020) for populations of wood turtles in the state. Conservationists have implemented nest protection (Bougie et al 2020) and head-starting programs in Wisconsin, although there is no empirical evidence of head-starting success in the state.…”

“…Some threats to adult and juveniles include road mortality, increased predation by introduced predators, and flooding (Brooks et al 1992, Steen and Gibbs 2004, Fordham et al 2007, Parren 2013, Lapin et al 2019). Threats to turtle nests include flooding and predation, particularly due to increased abundance of mesopredators (Tucker et al 1998, Bodie and Semlitsch 2000, Bodie 2001, Marchand and Litvaitis 2004, Bougie et al 2020). Various management approaches are used to reverse declines; however, quantifying the efficacy of such actions is complicated because turtles possess long life histories, with generation times approaching 30 years (Gibbons 1987).…”

“…Most management efforts for turtles focus on early life stages because they are easily accessible; the location and monitoring of nests is straightforward. Moreover, common management actions for early life stages, such as nest protection (Buhlmann and Osborn 2011, Geller 2012, Bougie et al 2020) and head‐starting (Buhlmann et al 2015, Mullin 2019), are generally less expensive than increasing survival of older stages and they are effective for the stage class they target (Brewster and Brewster 1991, Mitchell and Mitchell 2015, Bougie et al 2020). Nest protection and head‐starting have different impacts on overall population growth rate.…”

“…Researchers have recently quantified vital rates including adult survival (Lapin et al 2019) and nest success (Bougie et al 2020) for populations of wood turtles in the state. Conservationists have implemented nest protection (Bougie et al 2020) and head‐starting programs in Wisconsin, although there is no empirical evidence of head‐starting success in the state. While nest protection is successful at reducing predation and increasing success, defined as the number of eggs that hatch in a given nest (Bougie et al 2020), and head‐starting can produce high survival rates for young wood turtles in other states (Brewster and Brewster 1991, Mitchell and Mitchell 2015), there are no estimates of the impact of these management actions on population growth rates for wood turtles in Wisconsin.…”