Snapping Turtle
Chelydra serpentina
Bradford County, PA
Species
Chelonians, or turtles, are characterized by one
thing- the shell. This makes them instantly recognizable. There are nearly
600 species of turtle worldwide, but only 19 of these species can be found
in our range. Five of these are collectively known as the "sea turtles"
because of their complete use of and dependence on the open ocean.
Besides the shell, turtles have four legs and a
tail. The jaws are covered in a horny substance which makes a beak; there
are no teeth. Turtles also possess an external ear structure known as the
tympanum. The tympanum functions to amplify the audio signal before it
reaches the brain. Turtles, like all reptiles, have dry skin covered in
scales, but unlike the lizards and snakes, who shed their skin in one solid
piece, the turtles constantly shed in small pieces. Thus, it is not unusual
to find a turtle with flaking skin. This is a normal part of the shedding
process.
Some turtles are terrestrial, such as the Box Turtle
(Terrapene c. carolina) and the Wood Turtle (Clemmys insculpta).
Others are considered semi-aquatic. Examples of this are the Map Turtle
(Graptemys geographica) and the common Painted
Turtle (Chrysemys picta). Still others are fully aquatic and
come to shore only to lay eggs. The before-mentioned sea turtles are the
most stunning example of a fully aquatic lifestyle.
The diet of most turtles is carnivorous. This is
especially true of the aquatic and semi-aquatic species. Turtles have a
horny beak but no teeth. The beak is specialized for tearing off bite sized
pieces. Therefore turtles are not limited by the size of what they eat.
Terrestrial turtles tend to be somewhat more omnivorous, eating a variety
of vegetable material along with animal protein.
Terminology
Turtles, more so than any other taxon, have specialized structures that require special names. A few of these follow.
Basking
If you spend a lot of time outdoors you have undoubtedly
seen turtles stacked upon logs and other structures along the pond edges.
Many hypotheses have been proposed for why turtles bask. It is widely believed
that turtles lay in the sun for the primary reason of thermoregulation.
For an animal that spends most of its time in the cold waters there must
be some way for it to raise its body temperature. This is exactly what
basking is believed to accomplish.
Another hypothesis for the function of basking is
removal of external parasites. Algae and leeches are major parasites of
turtles and when the turtles bask, they dry these marine life forms enough
that the algae dies and the leeches drop off to return to the water.
Why several turtles chose to bask on the same structure
while ignoring other structures is unknown. It is probably due to microhabitat.
Microhabitat is the term used to describe all of the features of a small
area. A favorable microhabitat includes the presence of sunlight, of nearby
vegetation, and water quality. The interaction of several characteristics
make a certain haul-out site appealing to turtles while others are ignored,
for one reason or another.
It should be noted that not all turtles bask. Several
species are fully aquatic and seldom leave the water other than to lay
eggs. These species include the Snapping Turtle (Chelydra serpentina),
the Softshell Turtles (Apalone sp.), and the Mud and Musk Turtles
(Family Kinosternidae). Other species, such as the Box Turtle (Terrapene
carolina) and the Wood Turtle (Clemmys insculpta) are almost
completely terrestrial, thus, although they do bask, it occurs less frequently
and is less obvious. The few turtles that do bask often are those referred
to as the semi-aquatic turtles. These include the Red-eared Slider (Trachemys
scripta) and the Painted Turtle (Chrysemys
picta).
Reproduction
Reproduction in turtles is quite straight forward.
Fertilization is internal and unlike the squamates the male turtle has
a true penis. Breeding in most species occurs in the spring after the hibernation
period. Most often mating takes place in the water, however Box Turtles
are the exception to this rule. After mating the eggs develop inside of
the females body until they are ready to be laid. All turtles lay eggs.
Eggs of some species are covered in a hard, calciferous shell while those
of other species are leathery and more reminiscent of a snake egg. Eggs
may also be spherical or elliptical, depending on the species.
Laying time is most often late spring, two to three
months after mating. Sandy soils near water are most often chosen as deposition
sites, but eggs will be laid anywhere where the soil is soft enough to
permit digging. The female begins by digging several test holes. She first
urinates on the soil to loosen it and allow easier digging. She then digs
the pit with alternate movements of her hind legs. If the soil conditions
are not right, the female will not deposit the eggs, but will fill the
hole with the excavated soil and move to another position to begin again.
These false nests or "test holes" also function in confusing potential
predators by giving them several identical nests to chose from, only a
small number of which contain eggs. Once a hole has been dug which the
female finds to her liking, she deposits the eggs. Following this, she
covers the eggs with the excavated soil, and compresses this with her shell,
urinating on the nest to help pack it down. In good years it is not uncommon
for females to "double clutch" or produce two sets of eggs. They may mate
a second time, or they may use sperm that is stored inside of their body.
The eggs remain in the ground for several months
before they hatch. The young turtles slit the egg with a specialized structure
called the "egg tooth." This structure is a hardened projection with the
sole function of opening the egg. A few days after hatching the egg tooth
falls off. The young turtle spends several days inside of the egg absorbing
the rest of its yolk before crawling out of its shell and digging its way
out of the ground. It is not uncommon for small turtles to be found with
some of the yolk sac still attached.
Young turtles of most species must then find the
water. Much research has been done with sea turtles on this subject and
the conclusion has been reached that they follow the reflection of the
moon on the water's surface. Young from nests made near human population
centers face the problem of artificial lighting. The young turtles follow
the brightest light in the environment and most often this is human-made
artificial lights. The young turtles are lured to highways and roadways
to their deaths.
Research has shown that other young turtles have the ability to seek
out and locate water sources, but exactly how they do it is uncertain at
this time.
Wood Turtle
Clemmys insculpta
Tioga County, NY
Families
Turtles are classified in the Class Reptilia, Order Testudines. They
are sometimes referred to as chelonians. There are 19 species and subspecies
in our range representing 5 families.
Family Dermochelyidae- Leatherback
Family Cheloniidae- Sea Turtles
Family Chelydridae- Snapping Turtles
Family Kinosternidae- Musk and Mud Turtles
Family Emydidae- Pond Turtles
Family Trionychidae- Softshell Turtles
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