Assessing Changes in Bog Turtle (Glyptemys muhlenbergii) Population Abundance and Factors Influencing Nest Predation in Virginia

Across the globe, wildlife populations are facing increasing challenges, with many taxonomic groups significantly declining. Among endangered vertebrates (including birds, non-avian reptiles, fishes, mammals, and amphibians), turtles are one of the most threatened groups with over 60% of the 356 recognized species classified as threatened or worse. Bog turtles (Glyptemys muhlenbergii), are among the most imperiled of North American freshwater turtles. These small, secretive turtles have declined by up to 90% in parts of their range, which consists of the Northern Population and the Southern Population, and spans the eastern U.S. from New York to Georgia. These declines are mainly documented in the northern part of their range, but recent work in North Carolina suggests that turtles in the southern part of their range are similarly declining. Prior to this research, surveys aimed at estimating abundance had not been conducted in Virginia since the late 1990's. The research described here was conducted as part of a state-wide population assessment of bog turtles in Virginia. For my first chapter, I conducted capture-mark-recapture surveys in six wetlands in Floyd County, Virginia during 2019 and 2020, and generated abundance estimates. These wetlands had been surveyed in the same manner in 1997, which provided me the opportunity to compare recent abundance estimates with those generated from the 1997 data. My analyses suggest that turtle abundance across these six sites has declined by approximately 50% since 1997. This decline appears to be driven by, but not wholly attributable to, the alteration and loss of habitat at 2-3 of the 6 sites.

Habitat loss is acknowledged as one of the major drivers of population declines throughout the range of the bog turtle, in addition to illegal collection for the international pet trade. Due to the life history traits of this species (long life span and low fecundity), the loss of an individual from any life stage from the population can have detrimental effects. While many turtle populations are not heavily impacted from periods of low reproductive success, numerous subsequent years of complete nesting failure can negatively impact population-level survival. Recent studies have suggested that anthropogenically subsidized nest predators may be playing a role in continued nest failure at certain wetlands. My second chapter investigated the factors associated with anthropogenic footprint (i.e., buildings) and infrastructure that may be driving nest predation by these subsidized predators. In 2019 and 2020, I conducted a field experiment in 35 wetlands which utilized artificial turtle nests to investigate variation in nest predation across Montgomery and Floyd Counties, Virginia. I found that increases in the percent of developed land-use and other metrics of anthropogenic disturbance significantly increased nest predation, while increases in the percent of land-use without roads or buildings significantly decreased nest predation.

The findings from these two chapters are consistent with population trends documented in other parts of the bog turtle range, and build upon prior studies to investigate drivers of nest predation. These results provide information that can be used by managers to aid in the conservation of this state endangered species, and suggest further courses of research for future projects.