Nathaniel Asp
Wood Turtle: Clemmys Insculpta
http://faculty.evansville.edu/hk33/turtle%20program/student%20web%20pages/pokeys%20stuff/Pokey.htm
Introduction:
Researchers believe turtles have existed on earth for more than 200 million years
and live or have lived on every continent except for Antarctica. Several species of turtles
live longer than the average human and can live to be over one hundred years of age.
Although turtles can be grouped together into a class, each individual species is different
including the rare wood turtle. The oldest wood turtle fossil can be found in Nebraska
and is nearly 6 million years old. This species is now considered threatened and the aim
of this paper is to familiarize the reader with the wood turtle and also discuss issues
related to conservation of this species. The species is very interesting and quite rare in
Minnesota, but at least three are documented as living in the Canon river/Arb right in
Carleton’s backyard.
Habitat:
Most turtles prefer either land or water, but the unique wood turtle resides in both
terrestrial and aquatic environments. Wood turtles are one of the most terrestrial in its
family and are almost always near moving water (Kaufmann, 1995). A few studies have
shown that wood turtles select their habitat instead of just using them randomly and also
that a wood turtle’s ideal habitat is riparian (Brewster, 1991; Ernst et a., 1994; Kaufmann,
1995). The wood turtle prefers to live in clear rivers, creeks, and streams with sandy or
gravel filled bottoms. Wood turtles also favor basking in open fields and thickets, usually
more than half a mile away from developed or populated areas. Wood turtles seem to use
their habitats differently depending on whether they are male or female. The female
wood turtles spend more time in open, terrestrial habitats which they use for nesting,
while the male wood turtles spend most of their time in the aquatic environment because
they prefer to mate in water. It is not uncommon to find a wood turtle in forests,
agricultural fields, meadows, or even swamps. Some populations studied have
demonstrated shifts in their habitats, and have spent the summer in terrestrial habitats
while spending the fall and spring in aquatic habitats.
The wood turtle is distributed throughout the North East and Great Lakes
regions. The North East region stretches from northern Virginia to Nova Scotia, and the
Great Lakes region stretches from upper Michigan through Wisconsin and a small portion
of Minnesota. Fossils indicate that the wood turtle’s population once stretched as far
south as Georgia, but that this could have changed due to the warming conditions on
earth (Brooks, 1992). The Canadian populations of wood turtles are very scattered and
limited by the weather and the amount of streams and rivers that suit the wood turtle’s
habitat necessities. The wood turtle is sensitive to water temperatures and many of the
streams and rivers in Canada don’t meet their criteria, therefore the population is limited
to the areas that do meet their criteria. Despite this, Canadian wood turtle populations do
exist in most of New Brunswick, southern Quebec, north-central Nova Scotia, and most
of Ontario.
North American Distribution
Figure: Brooks et al., 1992
Physical Description:
The wood turtle (Clemmys Insculpta) is a medium-sized turtle, with the largest
turtle found on record having a shell of approximately nine inches. The wood turtle has a
broad carapace (upper shell) which is either brown, tan, or grey in color and it is
exquisitely decorated with black and yellow lines. The shell is wide and broad, with
widely flaring posterior marginals (Carr, 1952). The scientific name for this turtle means
“sculptured turtle”, referring to the look of its shell. The sculpted look of the shell is
brought out by the easily noticeable, well-defined growth lines, also called annuli.
The head of the turtle is also medium-sized, and the upper jaw is notched at the
tip. The head, neck, and legs are usually dark in color (brown or black) on top, and an
orange, yellow, or red color below. Sometimes however, the head and other parts of the
body may contain faint yellow dots. Brooks (et. al, 1992) demonstrated that turtles in
northern populations are larger and older at maturity than those in the southern
populations. This outcome can be explained because a larger size allows a build up of
larger energy stores, enabling a lower metabolic cost per unit weight, so the turtles are
able to survive the long winters and reproduce with a much lower risk of energy
depletion.
The size of wood turtles differs depending on the sex of the turtle. Males tend to
be proportionately larger then females and have larger heads, legs, necks, claws, and
limbs. In male turtles, the vent is located beyond the rear carapace where the tail is
extended, while in females, the vent is located right at the edge of the carapace. Another
distinguishing trait is that males have typically higher carapaces then females. The turtle
is very attractive to humans due to the bright colors of its shell and under body.
Reproduction:
Mating in wood turtles can occur at any time, although it primarily occurs during
the spring and fall months. While courting, both the male and female let out a whistling
sound, which is loud and persistent. The wood turtle then breeds in a very unique way; it
has often been referred to as a type of dancing. Mating for the most part occurs under
water and is a very lengthy process for this species of turtle. The process has been
recorded as lasting anywhere from one hour to two days long. The male and female
turtle approach each other very slowly with their necks extended and heads held high,
until they are within approximately 8 inches of each other when they drop their heads and
begin swinging their bodies from side to side. The male then takes the initiative by
placing his feet on the females shell, or near her face, and attempting fertilization. The
male usually takes the initiative as the aggressor, but in one instance reported by Carr
(1952), the female twice turned and tipped up the male from below, and crawled under
him.
Nesting for wood turtles usually takes place between the months of May and July.
Wood turtles nest on land and prefer to nest in areas of well drained soil and easy access
to the sun. The female then lays 5-18 eggs per year (all at one sitting), and most
hatchlings emerge anywhere from mid August to early October.
http://critterguy.museum.msu.edu/FieldGuide/Query.html?animalType=Turtles&animalGenus=Clemmys&
animalSpecies=insculpta&animalSubSpecies
Diet:
The wood turtle is in no way a picky eater, and has been found eating a wide
variety of plant and animal foods (is an omnivore). Animals they eat include earth
words, spiders, slugs, flies, fish, beetles, tadpoles, snails, and larvae. The plant life they
feast on includes moss, algae, berries, an abundance of different green plants, leaves, and
fungus. Wood turtles are said to eat ‘opportunistically’ when they are hungry and will
settle for anything they can subdue and swallow. Wood turtles also posses the unique
quality of being able to eat both on land and in the water.
The wood turtle has been observed using a unique method to catch earthworms
known as “earthworm stomping”. The turtle stomps on the ground with his foreleg
keeping to a constant rhythm. Every minute or so, the turtle begins digging with the
same leg and then stomping again until an earthworm emerges and he has a meal. These
stomping session can last for a considerable amount of time, anywhere from 15 minutes
to 4 hours, and can be quite loud. The earthworm rises to the surface because of the
natural tendency of an earthworm to rise to the surface when it senses rhythmic vibrations
in the ground caused by rain.
Threats & Conservation:
Wood turtles are state threatened in Minnesota and Wisconsin; state endangered
in Iowa and a species of special concern in Michigan. There are several concerns in
relation to the sustainability of the wood turtle population, but the biggest of those
concerns is habitat alteration.
Habitat Alteration:
Habitat fragmentation, loss and degradation are among the foremost reasons for
the observed declines in wood turtle populations. The wood turtle was once a very
widespread species of abundance, but due to the damages to their environment by human
activity (changing landscape etc.), the range and the population size of the species has
been reduced and the species has been declared endangered and threatened in some
states. In Minnesota particularly, much of the land has been flattened and turned into
farm land, hence destroying the habitat of the wood turtle. Not only is there habitat being
destroyed, but the presence of farm machinery only dampens their chances of adaptation
to the new environment. Another example of habitat fragmentation is Minnesota is the
expanding real estate along the shore of the canon river. More condominiums and houses
are being built along the river and invading on a prime habitat for several species. One
positive in Northfield are Carleton and St. Olaf’s contributions to restoration and the
purchasing of land. The canon river, which runs through Carleton’s arboretum, is host to
a very small population of wood turtles, so it is very important that conservation efforts
remain intact.
Another negative in relation to habitat fragmentation is that the wood turtle is
forced to move around to suitable areas in times of nesting. If the habitat has been
fragmented, the wood turtle may have to cross a road or railroad track and therefore is at
a much higher risk of mortality. In fact, many wood turtles are killed every year as they
attempt to cross roads to nest. Another problem this creates is after the juveniles have
hatched, they must cross back across these roadways in order to reach the water. Juvenile
wood turtles already have a very high mortality rate, and adding more threats only
increases that. Another threat to the wood turtle is animal trade.
Photo: Raymond A. Saumure
Animal Trade:
The wood turtle is legally protected throughout almost all of its range, yet it is still
heavily incorporated in illegal animal trade. Wood turtles are a very attractive species
and are sold at up to $1000 each. Wood turtles are most vulnerable to being caught in the
spring when the vegetation surrounding ponds and streams is not fully grown, and also
during hibernation and nesting. The population of wood turtles in the U.S. has been
decreasing and Canada has been a more recent target of the animal trade market. Every
turtle is important, as studies show the even removing one turtle can precipitate the
decline of a population (Garber & Burger, 1995). Wood turtles are a species that lives for
a long time, and they take many years to reach sexual maturity; combine that with a high
juvenile mortality rate, and the population is clearly reliant on its mature population. If
one member of the mature population is removed, it could be devastating to the rest of
the population. Another large threat to the wood turtles is predators and parasites.
Predators:
Populations of natural predators of the wood turtle may also increase due to
human involvement. For example, the raccoon population has increased as human
populations have increased because they are able to scavenge and find food more readily
and easily. Also, as more and more land is cleared off for agriculture, raccoons have to
search for food in unnatural areas. Natural predators of the wood turtle include raccoons,
otters, beavers, ravens, opossums, skunks, foxes, and coyotes. Also, wood turtles can
host a variety of parasites that can eventually kill them. A large number of wood turtles
are often found dead and mutilated by predators. The raccoon, whose population has
grown, is known as the number one predator responsible for mutilation of the wood
turtle’s limbs. These predators also prey on the nests of the wood turtle which only adds
to the problem of sustainability for this species.
Photo: Raymond A. Saumure
Conservation Conclusions:
Wood turtles are vulnerable to vast population decreases and even extinction
because they are hunted and harvested by humans and are not effective dispersers. Also
key on the future success of sustaining the wood turtle population is improving the
sustainability of the juvenile population. This may require the monitoring of its predators
and paying close attention to overpopulation of any of its predators. It is said that one
adult wood turtle is equivalent in importance to 50-100 juveniles because the success rate
of a juvenile is very low. To eliminate the unhealthy threats, organizations have
protected different areas and habitats. This is integral in sustaining the wood turtle
population because they do require a unique habitat in that they need both aquatic and
terrestrial. The most important means of sustainability is conserving its habitat and
making sure they are in a natural setting. I would recommend a more aggressive
approach in removing the overpopulated predators of the wood turtle and also push for a
much harsher fine if caught capturing or selling the wood turtle in any illegal means.
This may help sustain the gradually decreasing wood turtle population. The Arboretum
at Carleton College is one investment that just may save a small portion of the wood
turtle!
References:
Brewster, K.N., & Brewster, C.M. 1991. Movement and microhabitat use by juvenile
wood turtles introduced into a riparian habitat. Journal of Herpetology. 25(3): 379-382.
Brooks, R.J., Shilton, C.M., Brown, G.P, & Quinn, N.W.S. 1992. Body size, age
distribution, and reproduction in a northern population of wood turtles (Clemmys
inscuplta). Canadian Journal of Zoology. 70:462-469.
Ernst, C.H., Barbour, R.W., & Lovich, J.E. 1994. Turtles of the United States and
Canada. Smithsonian Institution Press, Washington, D.C. 578p.
Garber, S.D., & Burger, J. 1995. A 20-year study documenting the relationship between
turtle decline and human recreation. Ecological Applications. 5(4):1151-1162.
Kaufmann, J.H. 1995. Home ranges and movements of wood turtles, Clemmys insculpta,
in Central Pennsylvania. Copeia. 1995(1):22-27.
Carr, Archie Fairly, 1952. Handbook of Turtles; the turtles of the U.S., Canada, and Baja,
CA. Cornell University Press, Ithaca, New York.
Interview: Non-Game Specialist- Barb Henry (507)-280-5021