Turtle Ecology & Life History
All turtles, tortoises, terrapins, and sea turtles (animals with a backbone and a shell consisting of bone) are classified under the Order Testudines. Out of roughly 330 turtle species worldwide, North America has 56 different species. The Eastern United States claims the highest level of diversity. Turtles are found in all of the world's oceans and on all continents except for Antarctica. Habitat ranges from oceans to rivers, marshes, rainforests, deserts, and even mountains. Turtles in Wisconsin are associated with lakes, rivers, streams, ponds, and bogs; however, they are also found commonly foraging for food on land. Even though turtles reside in all corners of the world, they are considered the most threatened of vertebrate species. The International Union for Conservation of Nature (IUCN) 2011 Red List claims 45.2% of all turtle species to be threatened and 29.9% to be endangered or critically endangered. Of the 11 species of turtles in Wisconsin, one is endangered (Ornate Box Turtle), one is threatened (Wood Turtle), and three are of Special Concern (Blanding’s Turtle, Smooth Softshell and False Map Turtle).
Turtles are active primarily from April to October. Their daily activities generally include sleeping, basking, and foraging for food. Depending on the species, turtles can be omnivores, herbivores, or carnivores. Algae, fruit, stems, leaves, and invertebrates are consistent turtle food sources. For mobile prey, turtles use methods such as ambushing or stalking. In many cultures, turtles have been associated with age and wisdom. Some species have been documented to live 100+ years, while a few Giant Tortoises are thought to have lived up to 150 years.
Turtles have slow maturation rates. Sexual maturation in certain species can take as long as 20 years. Mating primarily takes place in late spring and involves males courting females. Once fertilization takes place, females usually instinctively migrate to upland nesting sites in June and July, excavate a nest, lay eggs, and cover the nest with soil. From August to September, hatchlings begin to emerge and head for water and cover. Turtles do not display parental care once the eggs are laid. The sex of hatchlings is dependent on incubation temperature, with females being produced in warmer soil and males resulting from cooler soil. Prior to the onset of winter, turtles begin to hibernate beneath soil and plant debris of woodlands and prairies or in the soft muck at the bottom of waterways.
Turtles are important to a variety of human cultures. For thousands of years turtles have been used by humans for food, medicine, and tools. Their long lifespan and proclaimed wisdom have helped form cultural identity and ideology across the globe. Scientists have been unraveling turtle mysteries such as their grand impact on soil formation, maintenance, and functions, as well as their abilities to pose as proficient seed dispersers and germinators for many types of plants. Turtles, like amphibians, are excellent indicators of environmental pollution. Due to their place in the food web, they have the ability to accumulate high levels of toxins such as mercury, lead, DDT, and PCB's in their bodies. Some turtles have been labeled as keystone species in their associated ecosystems. For example, the burrows of the Gopher Tortoise serve as habitat for a plethora of additional species that couldn't live in certain ecosystems without these burrows.
Once abundant, turtle populations across the world have steadily been declining throughout the last few decades. Habitat loss and degradation, including fragmentation, is a leading cause of species rarity. Once discovered, abundant turtle populations are often overexploited for use in the exotic pet and foreign food trades. In most cases, adults are being over-collected to the point that repopulation is non-existent. Increasing pollution concentrations in waterways can often be cited as a factor negatively affecting population levels. Diseases are also frequently transmitted to turtles from humans, domestic animals, or even invasive species. Among other things, introduced invasive species often eliminate natural biotic relationships turtles need to survive, increase prey on eggs, and displace turtles from niches they once fit into.
Turtle Research & Conservation
In order to conserve rare species such as turtles, it is necessary to promote education awareness on the biology and plight of these reptiles. Volunteers and interested citizens are important field technicians to the WDNR in that they can gather data to be used for research analyses used to benefit turtle populations. Volunteer assistance can be as easy as observing and reporting road crossing mortalities, turtle nesting areas, and local population occurrences. These data can be used to implement turtle crossing structure studies or to initiate mapping turtle movements across the landscape. As important as all these measures are to conservation, it is imperative to create and enforce regulations that protect and improve natural landscapes from human impacts and pollution, establish buffer zones around wetlands and other turtle habitat, and manage the illegal take of wild caught turtles for use as pets across Wisconsin.
Christoffel, R., R. Hay, and M. Monroe. 2002. Turtles & Lizards of Wisconsin. Wisconsin Department of Natural Resoruces, Madison, Wisconsin. (book)
Ernst, C. H., and J. E. Lovich. 2009. Turtles of the United States and Canada. 2nd Edition. The John Hopkins University Press, Baltimore, Maryland. (book)
Turtle Taxonomy Working Group 2011. Turtles of the world, 2011 update: annotated checklist of taxonomy, synonymy, distribution, and conservation status. In: Rhodin, A.G.J., Pritchard, P.C.H., van Dijk, P.P., Saumure, R.A., Buhlmann, K.A., Iverson, J.B., and Mittermeier, R.A. (Eds.). Conservation Biology of Freshwater Turtles and Tortoises: A Compilation Project of the IUCN/SSC Tortoise and Freshwater Turtle Specialist Group.