Blanding’s Turtle (Emydoidea blandingii): A Technical Conservation Assessment

Authors

Justin D. Congdon, University of Georgia School of Law
Douglas A. Keinath, University of Wyoming

Date of this Version

7-20-2006

Citation

Congdon, J.D. and D.A. Keinath. (2006, July 20). Blanding’s Turtle (Emydoidea blandingii): a technical conservation assessment. [Online]. USDA Forest Service, Rocky Mountain Region. Available: http://www.fs.fed.us/r2/projects/scp/assessments/blandingsturtle.pdf

Abstract

Blanding’s turtles (Emydoidea blandingii) are secure in Nebraska, and they range from being vulnerable to threatened, or endangered throughout most of the rest of their distribution. In Region 2, they have not been reported from Kansas, they are extremely rare in South Dakota, and they occupy wetlands in the northern half of Nebraska. The largest population known within the range of Blanding’s turtles is at Valentine National Wildlife Refuge, Nebraska.

The core habitat of Blanding’s turtles has an aquatic component that consists of a permanent wetland and a suite of other, usually smaller and more temporary, wetlands such as vernal pools that are used by adults and hatchlings as temporary refugia and seasonal food sources. Blanding’s turtle habitat also has a large terrestrial component that consists of nesting areas and movement corridors. The terrestrial component of the core habitat is larger than that of many other aquatic turtle species, and both sexes use terrestrial corridors for movements among wetlands and for nesting migrations.

A host of things can affect Blanding’s turtles through their impact on either (or both) the wetland or terrestrial portions of their required habitat. Given the wide range of possible threats to populations of Blanding’s turtles, three categories of threat appear most important. In rough order of decreasing priority, they are as follows: loss and degradation of wetland and terrestrial habitats; road mortality; collection

Loss and degradation of wetland and terrestrial habitats: Destruction of resident aquatic habitat is of primary conservation concern because it impacts all stages of the life cycle. Reduction in the numbers of such wetlands can increase risks of mortality for adults and reduce hatchling recruitment into populations. Cultivation to the edge of wetlands and the use of fertilizers, pesticides, and herbicides that wash into wetlands can degrade aquatic habitats. Water management activities related to fish management and agriculture can be detrimental to overwintering Blanding’s turtle populations if they are conducted during winter.

Loss or degradation of terrestrial movement corridors can increase the risks of injury and mortality, and in addition may lead to isolation of populations and a subsequent reduction in genetic variation through drift and inbreeding. Reduction in the amount or number of nesting areas through agriculture, forestry, forest succession, introduction of exotics, or development can result in increased risks to females during nesting migrations of longer length or duration. Despite their importance to Blanding’s turtles and the amphibian larvae that they feed on, small and temporary wetlands have minimal or no legal protection in many areas. However, conservation easements, local zoning, and education of private and public landowners can help reduce the loss of Blanding’s turtle habitat. Such protection must focus on both wetlands (including small wetlands such as vernal pools) and key terrestrial areas near those wetlands.

Road mortality: The propensity for terrestrial movement by Blanding’s turtles results in added risk of adult mortality associated with roads and other human activities, problems that tend to impact females more than males because of their extensive nesting migrations. In Michigan we have found females killed by farm equipment such as tractors, hay mowers, and road graders, and some stuck in stock fences. Communicating conservation issues to transportation planners may reduce construction of new roads in movement corridors and between nesting areas and aquatic habitats. Designs for new roads with high traffic volumes should include both barriers and culverts to control turtle movements. Barriers should block access to risky areas and encourage use of culverts that allow turtles safe passage under roads. Road signs can be placed along roadways with high volumes of traffic of both Blanding’s turtles and vehicles. In areas with high levels of mortality associated with existing roads, fencing and ecopassages (e.g., culverts, tunnels, bridges) should be installed.

Collecting: In conjunction with their extended longevity and long reproductive lives, collection of adults, juveniles, and hatchlings from small and isolated populations for the pet trade can result in severe reductions and extirpation of populations. Gravid females were collected on roads by motorists during nesting migrations; one was subsequently returned to the University of Michigan’s Edwin S. George Reserve (ESGR) when it was found to be marked.

The presence of these threats is exacerbated by a number of factors that make Blanding’s turtles particularly susceptible to disturbance. First, Blanding’s turtles and many other turtle species have temperature-dependent sex determination and some populations have biased adult sex ratios (e.g., the ESGR population in southeastern Michigan has an adult sex ratio close to 1 male to 4 females). Biased sex ratios are one of the factors that reduce effective population size and can contribute to population instability and reduce the probability of population persistence, particularly for small populations. Further, head-starting programs that include protecting or moving nests to artificial nesting areas run the risk of producing highly biased hatchling sex ratios. Second, reproductive output of Blanding’s turtles is low. Females do not begin to reproduce until they are between 14 and 20 years old, do not reproduce every year, and have small clutch sizes, thus resulting in low fecundity. This means that annual survivorship between ages 1 and maturity must average at least 60 percent to maintain population stability. Third, Blanding’s turtles are long-lived (even compared to other turtles), and older females appear to have higher survivorship and reproductive output than do younger females. This places primary reproductive importance on a small segment of the population, and because potential reproducti