Along with our partners, we have been monitoring the Blanding’s turtle population within the Lake Plain since 2004. This large coastal area represents one of the largest and most well-studied populations of Blanding’s turtles in the region. However, modeling has indicated that the population is in decline due to low juvenile recruitment combined with unsustainable levels of adult mortality. In an effort to address the decline and recover the species, we instituted the Blanding’s Turtle Recovery Program in 2010. Learn more »
A viable, free-ranging population is defined as a population consisting of at least 50 adults that exhibits natural recruitment for at least two generations or 74 years. Natural recruitment is indicated by individual turtles reaching sexual maturity via natural means and unaided by management activities such as nest protection, head-starting or predator management. We have identified focal conservation areas (FCA) based on known population size (> 20 individuals) and the amount of nearby protected habitat (> 500 acres). Though three FCA were identified, we have recommended that conservation efforts be focused on the Lake Plain in northeastern Illinois and southeastern Wisconsin.
The Blanding’s turtle population contained within the Lake Plain is arguably the largest and most significant in the state and warrants the focus of management attention. Since 2004, 855 individual turtles have been documented in two sites within the larger coastal area, including 538 turtles that were released as part of a head-starting program. These two monitoring areas encompass only 530 of the roughly 5,000 acres (10.6 percent) protected within the entire FCA. As such, the population across the entire Lake Plain is likely significantly larger but is largely unknown, as little monitoring has been conducted within the remainder of the Lake Plain.
Despite the seemingly robust population size and abundance of habitat, modeling at one of the Lake Plain sites indicates that this population is in decline. The decline can be directly attributed to low survival rates for both juvenile and adult life stages. Data from 2004–2010, found only 7.7 percent of turtle nests hatched successfully without the aid of protection from predators. Annual adult survival was estimated to be 88 percent, which is well below the 95 percent believed necessary to sustain a long-term population. This means that not enough turtles are being produced on an annual basis to replace adults lost from the population. As such, we are monitoring to document population level changes and focusing conservation efforts to address these issues.