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According to the oral stories and traditions of the Great Lakes Woodland Indians, the turtle is a powerful symbol. One legend details how the turtle's back provided a base for the first land that was formed in the midst of the great waters. Mackinac Island takes its name from a word in the Ottawa language meaning "Great turtle". Even today, turtles hold power and meaning in our lives. Turtles are an important link in the web of our living planet and it is up to everyone to ensure they remain.
The earliest fossil remains of turtles date back about 225 million years to the late Triassic period. For millions of years they shared the planet with the dinosaurs. Unlike the dinosaurs, turtles survived the ecological and climatic changes that caused the extinction of many forms of life. All this was accomplished with little change to their anatomy: early fossils still closely resemble today's turtles. Soft bodies were covered by a bony shell, with an oval shaped skull and beaked mouth; however these early turtles had teeth and had not yet evolved a way of pulling their heads into their shells. Today some 260 species of turtles (including the terrestrial tortoises) are found worldwide in nearly all temperate and tropical habitats.
The protective shell is one key to the turtle's survival. Unlike the turtles in children's cartoons, real turtles cannot climb out of their shell: A turtle literally wears part of its skeleton on the outside of its body. A turtle's shell is composed of two parts. The upper portion, or carapace, is formed from the flat dermal bones covered by broad scales (scutes) and is connected to the backbone and ribs. The lower shell is the plastron and includes the abdominal ribs and portions of the shoulder girdle.
The shape and weight of a turtle's shell can provide clues to its lifestyle. Shells can be helmet shaped, like the Blanding's and eastern box turtle shells, for better protection against predators. A further adaptation of hinges in the middle of the plastron allows these turtles to partly or fully close their shell, offering even more protection for the head and legs. Shells can also be soft and rubbery like the pan caked shaped shell of the fast swimming spiny soft shell turtle, which is covered by skin instead of hard scales. Snapping and Musk turtles have very small, cross shaped plastrons, probably adapted to facilitate walking on pond and lake bottoms. Land living turtles have heavier shells - while these shells offer extra protection from land predators, their weight makes it more difficult to move quickly. The shell of a turtle that spends most of its life in a water environment is lighter in weight and more streamlined in shape.
The turtles' environment includes a unique blend of niches from wetlands, to uplands, to sand sites. Each niche is important to satisfy the separate living, breeding, and feeding requirements of Michigan turtles. When these special habitats are changed or impacted, either through development, chemical contamination, or wetland drainage, the futures of many turtles are placed in jeopardy.
Like all ectothermic (coldblooded) animals, turtles depend on the sun as an external source of heat to maintain life and normal activity. They spend much time basking on logs, stream banks or other open, sunny places. A basking turtle is able to obtain a body temperature several degrees warmer than the air. In addition, direct sun exposure helps to discourage parasites such as leeches and algae and facilitates production of vitamin D in the skin. Vitamin D is needed to process calcium, important in the growth of the shell and other bones.
Two of the best times to view turtles are in the spring, and fall, when turtles sun the most.
As winter approaches and they are no longer able to maintain a warm enough body temperature, turtles decrease their feeding activities. Most Michigan turtles burrow in to the bottom soil of lakes, ponds, and streams to survive the long Michigan winter. The box turtle, a land hibernator, is the exception. Box turtles dig shallow burrows into woodland soil and leaf litter and are able to survive subfreezing temperatures for many weeks. Even during winter dormancy, turtles occasionally change position, and some, like the painted and Blanding's turtles, can be seen moving slowly about under the ice.
All turtles breathe with lungs, but many aquatic species such as the softshell turtles can absorb oxygen while submerged, either through their skin or by passing water over membranes in the throat or cloaca (an internal chamber that opens at the base of the tail).
A turtle's beak will reflect its diet. Turtles that eat flesh have hook shaped beaks similar to most raptors. These hooked beaks easily slice and tear food apart. Those that eat vegetation or shellfish have flat, wide beaks useful for mashing a meal. A few turtle species are largely carnivorous (e.g., Musk, Map, Blanding's, and Softshell turtles). Most, however, eat both plants and animals.
Young Sliders, Painted, Eastern Box, Spotted and Wood turtles consume mostly insects and other small animals but eat more plants and fruits as adults. Contrary to popular belief, most turtles do not consume large numbers of game fish and have little or no impact on fisheries management. Since they are opportunistic feeders, Snapping turtles occasionally capture fish and young waterfowl.
Turtles reproduce by internal fertilization and produce shelled eggs deposited on land. Most mating takes place in spring after a brief courtship, which begins shortly after turtles emerge from their hibernation sites. Courtship displays vary greatly. Male Eastern Box turtles chase their intended mates and nip at their shell edges, or chin. Female painted turtles receive soft toenail strokes from potential mates. Male snapping turtles may fight fierce battles to drive rivals away from a choice breeding territory.
Between late May and early July, a female turtle will leave the water and seek a sunny spot with little or no vegetation and moist, but not saturated, sand or soil. She digs a shallow nest cavity with her hind feet and deposits her clutch of eggs. Depending on species, the eggs may be round or oval and have either hard or flexible shells. The nest is then refilled by the female with excavated materials, without ever having seen the eggs and is abandoned to its fate. Many (probably most) turtle eggs are eaten by raccoons or other predators within a few days of being laid. Those that survive will hatch in two to three months. In most cases, the young head immediately for cover in shallow water (aquatic species) or leaf litter (box turtles). Young painted turtles have the ability to withstand partial freezing and often remain in the nest over winter, emerging in spring.
In most turtle species, gender is determined by the temperature of the egg during a critical part of incubation. In general, male turtles tend to hatch from cooler eggs, and females hatch from warmer eggs. Once hatched, baby turtles can grow quickly for the first few years, with growth slowing as they near adulthood.
Turtles are among the longest living animals on earth. Several species of turtles can live for several decades. With this longevity also comes a negative side. It takes several years for turtles to sexually mature (4 to 10 years for a Painted turtle, 14 to 20 years for a Blanding's or Wood turtle, and 15 years for a Snapping turtle). Non breeding turtles are often the targets of predators, automobiles, and pet seekers. In addition, the longer life span allows turtles to build up environmental toxins in their tissues. These toxins can have serious affects on a turtle's health and breeding ability.
Turtle stories can be found in many cultures around the world. Most often, they represent peace, patience, and most appropriately, long life. Images of turtles can be found cast in stone, molded into clay figures, and in cooking and food gathering utensils. Turtle designs are found in rock and colorful sand painting, and used in various quilts and cloth weave.
In stories, poetry, nursery rhymes, and songs, turtles are cast as featured characters. The role of the turtle in earth legends is common in Native American culture. Even today, turtles can be found as important characters in young adult movies and comics.
Draining of wetlands, increased residential, and commercial development has reduced the habitats of both aquatic and land turtles. Increased development also encourages runoff of contaminants into watersheds, increased traffic volumes, and predators. Raccoons are efficient predators of turtle nests. In some areas, they have been shown to reduce hatching success to zero.
Turtles can also be impacted by chemical and mechanical weed control in lakes and ponds.
Archeological remains of food gathering tools, fasteners, and storage containers made of the sea turtle are evidence that turtle parts have been used by people for thousands of years. However, due to the slow maturation of turtles, experts agree most turtle populations can sustain very little, if any, harvest or collection before populations begin to decline. Today, collection/harvest is primarily for commercial trade: shells, pets, or for turtle parts in medicines and as food, but even collection for personal use is a problem for rarer species.
Michigan law protects all but snapping turtles from commercial harvest, and the wood, spotted, eastern box and Blanding's turtles are completely protected.
Help turtles be a part of our world so their offspring can be a part of our children's future.
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