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.
History & Adaptation
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.
Habitat
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.
Behavior
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).
Food Habits
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.
Breeding
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.
Turtles in Art, Literature, and Mythology
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.
Conservation
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.
How You Can Help
- Learn all you can about our native turtles. Check out the library and
visit parks and nature centers that offer turtle programs.
- Know your state and federal laws that protect turtles and their habitats.
- Support efforts to protect wetlands and adjacent uplands used by turtles.
- If you are a riparian landowner, you can learn how to create open nesting
areas near water.
- Never buy wild caught turtles from pet dealers.
- Do not release captive reared turtles into the wild.
- Be alert for turtles crossing roads. If it can be done safely, you can
slow down or even stop to help a turtle cross a road. Always move it in the
direction it was heading.
- Enjoy watching turtles in the wild but resist the urge to take them home
as pets.
Help turtles be a part of our world so their offspring can be a part of our
children's future.
Michigan Species
Printer Friendly
Text Version 
Email Page
