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INTRODUCTION TO TURTLES FOR TOMORROW

Wisconsin is home to 55 species of amphibians and reptiles, known collectively as herptiles. Amphibians number 19 species, including 12 frogs and 7 salamanders. The reptiles, numbering 36, include 21 species of snakes, 4 lizards and 11 turtles. For several reasons, reptiles are often more vulnerable to large-scale human impacts on natural landscapes (e.g. habitat fragmentation) than amphibians.

Reptiles require much larger home ranges than amphibians.
For example, many amphibians can accomplish their full life cycle within 300 meters of their natal breeding ponds, whereas a number of snakes will often range in excess of one half mile, and sometimes much further, from their overwintering site to complete their life cycles.

Reptiles are slow to mature (requiring 3 to 20 or more years), requiring more time to replace lost adults in populations, whereas amphibians generally mature quickly (1-3 years). This difference is somewhat balanced by the fact that reptiles generally live much longer than amphibians.

Amphibians have higher reproductive capabilities than reptiles.
A female pickerel frog can lay 1,000 to 3,000 eggs annually, whereas a Blanding’s turtle averages laying 10-12 eggs per year.

As a result, reptiles are doing much more poorly than amphibians in Wisconsin, as well as in other parts of the country and around the world. The figure included below shows the status of the various herptile species by groups. You will quickly notice that reptiles face a far less certain future than amphibians. In fact, of the 10 herptile species currently listed as endangered or threatened, 90% are reptiles!

Of the rare reptiles, turtles perhaps face the most uncertain future. A number of U.S. and international conservation organizations consider turtles to be the most endangered species group in the world. Of the 300 species that occur worldwide, over 40 percent face potential extinction (Conservation International 2010). Many turtle populations suffer from a wide variety of threats ranging from habitat loss to road mortality to over-collecting and diseases.

Threats and Life History Factors that Influence Wisconsin’s Rare Turtle Populations

Several threats and natural limiting factors have contributed to the decline of rare turtles in Wisconsin in addition to the obvious loss and fragmentation of their habitats. These threats should help explain why Turtles For Tomorrow places an emphasis on rare turtle conservation above the other herptile species.

Delayed Maturity: The endangered ornate box turtle and the threatened Blanding’s and wood turtles are all very slow to mature. Ornates and wood turtles typically take 12-15 years to mature, while Blanding’s mature in 17-20 or more years. Compare this to Wisconsin’s five threatened or endangered snakes, where the slowest grower matures in 3-4 years.

Road Mortality: Blanding’s and wood turtles face some additional challenges since both are semi-terrestrial, requiring both aquatic and upland habitats to complete their annual life cycle. Blanding’s turtles often make long overland forays between various wetlands throughout the active season to find suitable foraging sites. In recent decades, woods turtles have become increasingly dependent on nesting along roads, especially near bridge crossings. As a result, both Blanding’s and wood turtles are often forced to cross roads, often resulting in road mortality at levels that further threaten their populations. Adult females are more likely to be killed on roads than other cohorts of their populations since they attempt to cross them more frequently due to their reliance on roadsides for nesting.

Turtle Nest Predation: Turtle nest predation rates have also significantly increased in recent decades. This has resulted from growing human populations that attract and help sustain higher levels of mammalian predators such as raccoons, skunks and fox. A long-term nesting study involving Blanding’s and painted turtles in Michigan showed that nesting success rates decreased from 8-44% in the 1970s to 0-5% in the late 1980’s and early 1990s (Congdon et al, 1993). There is no evidence to show that this trend has changed since the early 1990s. A sustained lack of sufficient reproduction will eventually lead to further population declines for all turtle species and could result in extirpations of rare turtles.

Over-collecting: For many years, wood turtles, along with many other herptiles, were harvested in large numbers to meet the demands of the biological supply industry, which supplied live and preserved specimens for classrooms and research from the late 1800’s into the 1970s. This market began to shift in the 1970’s to meet the demand for live herptiles in a rapidly growing world-wide pet trade. This is especially disconcerting given today’s very high nest predation rates. The annual loss of adult turtles, especially in long-lived slow-to-mature species must remain extremely low in order for populations to remain stable.

Other Threats: In Wisconsin these threats include the introduction of foreign diseases, and exotic plants that simplify or otherwise alter natural habitats (e.g. Phragmites Phragmites australis, also called common reed, and Spotted Knapweed Centaurea maculosa).

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