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TURTLES
Accessory Used: DC310 with Ext Flash and Diffuser
Location: British Virgin Islands
Photo by: Jeff Brooks |
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The gopher tortoise, Gopherus
polyphemus, with its unwebbed, stumpy feet, is an accomplished digger.
Burrows that may extend 10 m (35 ft) underground provide the turtle—and other
animals—with relief from extreme heat or cold. The gopher tortoise may share
its home with, among other guests, mice, gopher frogs, insects, burrowing owls,
opossums, or diamondback rattlesnakes. The burrow is often mistakenly attributed
to an actual gopher. |
Quick Tips
1. Always wash hands after handling turtles.
2. Never release exotic turtles or tortoises into the wild.
3. Never release a suspected sick turtle or tortoises into the wild.
4. Never feed raw chicken to turtles or tortoises. This may cause them to
contract salmonella.
5. Do not handle turtles or tortoises too often. this can cause stress to them.
6. Keep turtles and tortoises in a secure habitat to prevent escape and
discourage predators.
7. Provide proper habitat and adequate space for them.
8. Be informed of your particular species' eating and habitat requirements.
9. Do not acquire turtles or tortoises for a child who is not responsible enough
to provide proper care for them.
10. To dispose of unwanted pets, contact your closest turtle club or
herpetological society for adoption.
I.
Introduction
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Turtle,
reptile
with a bony or leathery shell. Any shelled reptile can be
called a turtle, but in North America people commonly use
the word tortoise
to designate members of a family of turtles that live
entirely on land, reserving the word turtle for
species that live in or near water. The word terrapin,
of Native American origin, is used in North America only
for the diamond-backed terrapin, a turtle that lives in
the brackish waters of eastern coastal marshes.
Turtles
are ancient life forms that first appeared on Earth during
the Triassic Period, which extended from about 240 million
to 205 million years ago. Turtles survived the disasters
that wiped out the dinosaurs and many other creatures at
the end of the Mesozoic Era about 65 million years ago.
The earliest known fossil turtles were similar to the
turtles that live today. The earliest turtles had teeth,
unlike today's turtles, which are toothless and use their
sharp jaws to bite and handle food. Early turtles also had
not yet evolved the ability to pull their heads into their
shells.
There
are about 270 living species of turtles, which are grouped
into 12 or 13 families. These families are further
classified into two suborders: side-necked turtles and
hidden-necked turtles. Side-necked turtles protect their
heads by folding their necks sideways under the top edge
of the shell. These turtles are found only in South
America, Africa, and Australia and nearby islands.
Hidden-necked turtles pull their heads directly into the
shell, using an up-and-down motion of the neck.
Hidden-necked turtles are more widespread than side-necked
turtles. They include all of the ocean-living and
freshwater turtles of North America, Europe, and Asia, as
well as the land-living tortoises. Sea turtles, as well as
a few other kinds of turtles, are considered members of
the hidden-necked group even though they cannot fully
withdraw their heads.
Turtles
inhabit every continent except Antarctica, in habitats as
diverse as ponds, rivers, and oceans; forests and
grasslands; and even deserts. Like all living reptiles,
turtles are ectotherms—cold-blooded animals whose body
temperature is influenced by the outside environment. For
this reason, turtles are most abundant in warm tropical
and subtropical climates. Eastern North America, however,
is home to numerous turtle species, despite its temperate
climate.
Turtles have long fascinated people of
many cultures, and they are often used to symbolize wisdom
and long life. In many Native American and Asian cultures,
turtles are mentioned in myths that explain the origin of
the universe. In China and Southeast Asia, turtles are
sometimes venerated in religious ceremonies. Despite the
reverence turtles have inspired, these animals have a long
history of being exploited by humans. People in many parts
of the world eat turtle flesh and eggs, and use turtle
parts in traditional medicines. Turtle fat is a source of
valuable oils. Some turtles, such as the hawksbill
turtle, are killed for their decorative shells, which
are the source of tortoiseshell used in jewelry. In
addition, many thousands of turtles and tortoises are
collected and sold as pets. By killing turtles, removing
turtles from their natural habitats, and destroying the
environments in which turtles thrive, humans have brought
many turtle species to the brink of extinction.
II.
Physical Description |
Turtles
vary widely in size. The world's largest turtle—the
great leatherback
sea turtle—reaches a shell length of 240 cm (96 in) and
can weigh over 900 kg (2,000 lb). The giant tortoises of
the Galápagos Islands, near South America, and the island
of Aldabra, off the East African coast, can reach at least
130 cm (50 in) in length. The largest North American
freshwater turtle is the alligator snapping turtle, which
can reach a shell length of 80 cm (31.5 in). Among the
smallest turtles are the American mud
turtles and musk turtles, which have a range that
extends from southern Canada through much of South
America. Many species in these groups are less than 13 cm
(5 in) in shell length. Other small turtles are the rare
bog turtle of the eastern United States, at 11 cm (4.5
in); and the tiny speckled cape tortoise of South Africa,
whose shell is only 10 cm (4 in) long.
| A.
Shell |
The
upper shell of the turtle, under which the head, limbs,
and tail can be more or less completely withdrawn, is
called the carapace. The lower shell, which encases the
belly, is called the plastron. The carapace and plastron
are joined together on a turtle's left and right sides by
bony structures called bridges. The inner layer of a
turtle's shell is composed of about 60 bones, including
portions of the backbone and the ribs. For this reason, a
turtle cannot crawl out of its shell.
In
most turtles, the outer layer of the shell is covered with
large horny scales called scutes. The scutes are part of
the turtle's outer layer of skin, or epidermis. Scutes are
composed of a fibrous protein called keratin, which also
makes up the scales of other reptiles. The scutes overlap
the seams between the shell bones, adding strength to the
shell. Some turtles, like the leatherback sea turtle and
the soft-shelled turtles, lack horny scutes, and instead
have shells covered with leathery skin.
Some
turtles have shells with flexible hinges that allow the
turtles to close off the openings in their shells through
which they withdraw their heads, tails, and limbs. These
hinges protect against predators and help prevent the
turtles from drying out when they are on land. Several
types of turtles, including Blanding's turtles, which
inhabit wetlands in the northeastern United States and
Canada, and the American box turtles, have a single hinge
across the plastron. American mud turtles have two hinges
on their plastrons. African hinge-backed tortoises have a
hinge across the back of the carapace.
The
shape of a turtle's shell provides clues about its way of
life. Most tortoises have high, dome-shaped shells. The
shape of these shells makes it difficult for predators to
crush these turtles between their jaws. An exception is
the African pancake tortoise, which relies on its flat,
flexible shell to hide in rock crevices. Most aquatic
turtles have flatter, more streamlined shells, which aid
in swimming and diving. American musk and snapping
turtles have small, cross-shaped plastrons that enable
greater leg movement for walking on the bottom of ponds or
streams.
Tortoises
have rather heavy shells. In contrast, sea turtles and
soft-shelled turtles that live continuously in water have
lighter shells, which help them avoid sinking in water and
increase their swimming speed and agility. These lighter
shells have large spaces called fontanelles between the
bones. The shells of leatherback turtles are extremely
light for their size because they contain many fontanelles
and lack horny scutes.
Turtle
shells are commonly brown, black, or olive green. In some
species, shells may have red, orange, yellow, or gray
markings. These markings commonly appear as spots, lines,
or irregular blotches. An especially colorful turtle is
the eastern painted
turtle, which has a yellow plastron and a black or
olive shell with red markings around its rim.
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B.
Head |
Most
turtles and tortoises have conspicuous eyes placed well
forward on the upper sides of their heads. Turtle species
that live most of their lives on land usually focus their
eyes downward toward objects in front of them. Some
water-living turtles, like snapping turtles and
soft-shelled turtles, have eyes nearer the top of the
head. These turtles can hide from predators and prey in
shallow bodies of water, where they lie nearly entirely
submerged except for their eyes and nostrils. Sea turtles
have glands near their eyes that produce salty tears,
ridding the turtles' bodies of the excess salt that they
take in from drinking seawater. When a sea turtle is in
the water, its tears are immediately washed away, but when
these turtles arrive on land, they look as though they are
crying.
Turtles
use their jaws to cut and handle food. Instead of teeth, a
turtle's upper and lower jaws are covered by horny ridges,
similar to a bird's beak. Meat-eating turtles commonly
have knife-sharp ridges for slicing through their prey.
Plant-eating turtles often have ridges with serrated edges
that help them cut through tough plants. Turtles use their
tongues in swallowing food, but unlike many other
reptiles, such as chameleons, they cannot stick out their
tongues to capture food.
Turtle
limbs, used for locomotion, are adapted to their
particular habitat. Land-dwelling tortoises have strong,
thick legs to support their heavy shells. They typically
move at slow speeds of less than 0.5 km/h (0.3 mph). The gopher
tortoise of the American southeast has flattened front
limbs that function as scoops for digging the deep burrows
in which it lives.
Aquatic
turtles move either by swimming or by walking on the
bottom of a body of water, such as a pond. Many aquatic
turtles, including painted turtles, sliders, and
soft-shelled turtles, have long toes connected by webbing.
These turtles spread out their toes to obtain a large
surface area for pushing against the water, which helps
them to dive and to swim quickly to escape predators.
Soft-shelled turtles are the fastest freshwater turtles
and can swim faster than most fish.
Sea
turtles are the most specialized swimmers of all turtles.
Their forelimbs are modified into flipper-shaped blades.
These turtles practically fly through the water, using
their hind feet primarily as rudders. Despite turtles'
reputation for being slow-moving animals, sea turtles can
achieve swimming speeds of more than 30 km/h (19 mph), a
speed an elite sprinter might reach for a short distance
on land.
Most
turtles have rather short tails, but the Asian big-headed
turtle has an extremely large, muscular tail covered with
protective scales that it can use to climb steep rocks and
logs in mountain streams. While climbing, these turtles
press their tails onto the climbing surface to support
their weight. The American snapping turtles also have very
long tails. Among most turtle species, males tend to have
longer, thicker tails than the females.
Turtles
breathe air with lungs, as do other reptiles and all
land-living vertebrates. Since turtle ribs are part of
their shell, turtles cannot move their ribs in and out to
expand or deflate their lungs. Instead, turtles
alternately expand and contract various groups of muscles,
including those in their abdomen and above their front and
hind legs, to change the amount of space within the shell.
When these muscles expand, less space is available and the
lungs are compressed, permitting the turtle to exhale. A
turtle takes in air as these muscles contract to provide
more space into which the lungs can expand. Many aquatic
turtles remain submerged in water for periods of several
hours to several days—and for many months during winter
hibernation. Many turtles are able to take in oxygen from
water through the linings of the mouth, throat, and an
internal chamber called the cloaca, as well as through the
skin. However, when they are active, aquatic turtles need
to rise to the surface periodically to breathe air with
their lungs.
Like
most reptiles, except for crocodiles and their close
relatives, turtles have a heart with three chambers. A
turtle's heart operates almost as if it had four chambers,
however, because one of its chambers, called the
ventricle, has an incomplete divider, or partition. This
divider helps prevent the blood that has received oxygen
from the lungs and is ready to circulate through the
turtle's body from mixing with blood that is depleted in
oxygen and needs to travel to the lungs for a fresh
supply.
In
a turtle's digestive system, food passes from a turtle's
mouth through a tubelike esophagus to the stomach, where
digestion begins. Food passes from the stomach into the
intestine, where nutrients can be absorbed into the
bloodstream. Wastes from the intestine are emptied into
the cloaca, from which the wastes leave the turtle's body.
Turtles also have a urinary system, which filters waste
products from the blood and excretes them through the
cloaca.
Turtles
have a central nervous system and a well-developed brain.
They have keen senses that they use to interpret their
world. Most turtles have sharp vision and can recognize
patterns and colors. The eyes of sea turtles are adapted
for seeing underwater, but they can see only short
distances when they are on land. Most turtles, including
sea turtles, have a good sense of smell. Both the shells
and the skin of turtles are sensitive to touch. Turtles'
ability to hear sounds that travel through the air is
limited to low frequencies, but they can perceive
vibrations transmitted through the ground or water.
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| A.
Temperature Regulation |
Like
all reptiles, turtles are ectothermic, or cold-blooded, animals
that control their body temperature by moving into or out of
warm or cool places. Unlike endothermic, or warm-blooded,
animals, such as mammals, turtles do not generate heat in their
bodies from digesting food. Leatherback sea turtles are an
exception, as they can produce internal heat in their muscles
while swimming, and their huge size, together with a thick layer
of oily fat under their skin, helps them retain this heat. As a
result, they can range into such extremely cold areas as the
North Sea. Other marine turtles can survive only in warmer
waters.
Many
activities of turtles help regulate their body
temperatures.Aquatic turtles often leave the water to bask in
the sun on logs or rocks or along the banks of lakes and streams
to warm their bodies. In winter, turtles that live in seasonal
climates enter a dormant state resembling hibernation. In this
state, called torpor, the turtles stop feeding and their oxygen
needs become very low. Aquatic turtles usually remain underwater
in winter, relying on their ability to obtain oxygen from water
through their skin, throat linings, and sacks within their
cloaca. In contrast, land-living turtles burrow into the soil.
Eastern box
turtles may spend the winter in shallow burrows; they are
able to survive partial freezing of their body fluids for
several days. Young painted turtles often spend their first
winter in an underground nest. These infant turtles have the
ability to survive sub-freezing temperatures for several days.
Most
turtles are omnivores—animals that eat both plants and other
animals. Most of the smaller pond-, marsh-, and stream-dwelling
species, including the American painted and slider turtles and
the European pond
turtle, eat insects, snails, worms, minnows, and tadpoles,
as well as aquatic plants. The terrestrial box turtles of North
America commonly
| IV.
Life Cycles and Reproduction |
Female
turtles have two ovaries—organs that produce eggs—and male
turtles each have a pair of sperm-producing organs called
testes. Male turtles, like male crocodiles, have a penis that is
located on the lower wall of the cloaca. The penis has a groove
on its upper side. During mating, sperm travels along this
groove and passes into the cloaca of the female.
Mating
among turtles often begins with ritualized courtship behaviors
by males. Depending on the species, some male turtles nip at the
female's shell or neck, or bob or swing their heads over the
female's head. Male painted and slider turtles vibrate their
very long foreclaws on the side of the female's head during
courtship. Female turtles that are not ready to mate may pull
into their shells or try to escape. Female green sea turtles
sometimes avoid a male's advances by swimming away or by folding
their hind flippers together.
During
mating, the male climbs on top of the female and inserts his
penis into the female's cloaca to release his sperm, which will
later fertilize eggs from the female's two ovaries. In many
species, the male's plastron has an inward curve that helps him
balance on the female's shell. Female turtles of some species,
including American box turtles and diamond-backed terrapins, can
store sperm and lay fertile eggs for up to four years after a
single mating.
Turtles
may mate either on land or in water, but all turtles lay their
eggs on land. Turtle eggs are either oval or round and are white
or nearly white, and they are covered with either thin and
flexible or fairly thick and rigid eggshells that protect the
eggs from drying out. Most female turtles bury their eggs in a
nest hole that they dig in the ground with their hind feet. This
nest site is chosen so that it provides proper warmth and
moisture for the eggs, as well as safety from flooding. The
number of eggs in a clutch—those eggs laid by a female during
one nesting—varies from 1 to about 200, depending on the
species. Most small species have clutches of between 1 and 6
eggs, but large species may have clutches that consist of dozens
of eggs. Sea turtles, such as the green
turtle, may migrate 2,000 km (1,242 mi) to find suitable
nesting beaches. These turtles must drag themselves along the
beach because their paddle-shaped forelimbs are not suitable for
walking. After covering the nest with dirt or sand, a female
turtle provides no further care for her eggs or young.
Many
turtle nests are destroyed by predators, such as raccoons,
foxes, and skunks, before the eggs can hatch. If they escape
being eaten, the eggs of most turtle species incubate for two or
three months before hatching, though a few species, including
some of the larger tortoises, require a year or more. For
reasons not well understood, for most turtle species, the
temperature of the egg about midway through incubation
determines the sex of the hatchling. For example, red-eared
slider turtle eggs kept below 28° C (about 82° F) will
produce nearly all male hatchlings; if kept above 30° C (86°
F), they hatch into females. At 29° C (about 84° F), both
sexes may result. In the American soft-shelled turtles and a few
other species, temperature has no effect on a hatchling's sex.
In these species, hereditary units called chromosomes may
determine sex, as is the case with birds and mammals.
Most
baby turtles grow quickly during their first years of life, but
growth soon slows. Depending on the species, it may take from 5
to 20 years or more before they are mature and able to
reproduce. Turtles are known for their long life spans. Many of
the smaller pond and river species can live over 30 years.
American wood turtles, European pond turtles, and snapping
turtles may surpass 60 years. American box turtles and European
tortoises sometimes reach the century mark, and captive giant
tortoises are reported to have lived for more than 200 years.
Turtles
have been a successful group of animals for over 225 million
years, but today the future of many species is in doubt. Though
well adapted to survive natural threats, the massive
environmental changes caused by human activities are proving to
be too much for these long-lived creatures. Some scientists fear
that human actions, including destroying turtles' natural
habitats, directly killing turtles, and even removing them from
the wilderness areas that remain, may result in the extinction
of many turtle species in the next few decades.
Turtles
and tortoises are losing vast portions of their original
habitats as humans convert wetlands, forests, and grasslands to
agricultural fields, grazing lands, and villages and cities.
Pollutants from farms and urban areas have degraded many turtle
habitats. Turtles are also harmed when humans alter rivers and
streams by creating dams and channels, or build sea walls or
jetties on the beaches where sea turtles lay their eggs.
Tortoises,
which are especially slow moving and easily captured, have long
been hunted by humans for food. During the 18th and 19th
centuries, whalers captured vast numbers of giant tortoises from
the Galápagos Islands to feed to their crews. These ships also
harmed tortoises by releasing rats and cats that ate tortoise
eggs and young tortoises. By 1900, few tortoises remained, and
several forms were already extinct. Efforts by conservationists
to breed Galápagos tortoises in protected facilities probably
saved them from extinction. Today many smaller mainland tortoise
species are also being killed in large numbers and could soon
disappear unless efforts are made to save them.
Freshwater
and marine turtles may be scattered over their habitats much of
the year, but all must return to specific shoreline sites to
nest, giving humans the opportunity to take both the female
turtles and their eggs for food. These nesting habits leave the
turtles vulnerable and nearly all sea turtles and many species
of freshwater turtles are now greatly reduced in numbers or even
threatened with extinction. Many sea turtles die in fishing
nets, and others are killed when they eat garbage that has been
thrown into the ocean. Hawksbill sea turtles are killed for
their thick carapace scutes, which provide the tortoiseshell
used to make combs, curios, and small art objects. Sea turtles
are also killed to make leather products. In Southeast Asia and
China, turtles are both eaten and used in traditional medicine.
A greatly increased Asian turtle trade in recent years has
brought many formerly common species to the brink of extinction
in this region.
The
pet trade, which affects mainly small terrestrial and
semi-aquatic species, is another threat to turtles. North
American box and pond turtles, as well as the small tortoises
found in the Mediterranean region, are particularly valuable to
pet trade collectors. In 1975, the United States Food and Drug
Agency banned the sale of turtles with shells measuring less
than 10 cm (4 in) because many turtles carry a type of bacteria
called Salmonella that can infect humans, causing severe
gastrointestinal distress. This ban reflects the concern that
young children might put these small turtles in their mouths.
Larger turtles are still sold as pets in the United States, and
turtle farmers can legally sell small hatchling turtles from the
United States to overseas markets. Due to the pet trade, slider
turtles that are native to the southeastern United States have
been spread to many parts of the world. In many instances these
pets have escaped human homes and started populations in the
wild. In some areas, these feral turtles have taken over
habitats once used by native turtles.
Compared
to other wildlife, turtles are particularly vulnerable to harm
from direct exploitation. Turtles' slow pace of reproduction is
normally compensated by the long lives of mature adults. Thus,
it is difficult for populations to recover after numerous mature
adults have been killed or removed. In such cases, the turtle
population inevitably declines and may eventually disappear.
Many
states and countries have passed laws to protect rare turtle
species. More than 130 nations have signed a treaty called the
Convention on International Trade in Endangered Species of Wild
Fauna and Flora (CITES), which regulates the international
transport of endangered forms of wildlife, including many
turtles and tortoises. Some countries, including the United
States, require large-scale shrimp fisheries to use nets that
contain turtle excluder devices. These devices help turtles
escape from fishing nets. Unfortunately, many wildlife laws are
difficult to enforce, and developing nations in particular may
lack the necessary resources for preventing the exploitation of
turtles. Unless people around the world take steps to preserve
turtles and tortoises within their natural environments, many
species of these intriguing and ancient animals will probably
become extinct during the 21st century.
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