Download section 2 – the physical, behavioural, and genetic characteristics of

SECTION 2 – THE PHYSICAL,
BEHAVIOURAL, AND GENETIC
CHARACTERISTICS OF THE EASTERN
MASSASAUGA RATTLESNAKE
Biology is the study of life. This endeavour involves understanding a species’
physical characteristics. It is also a study of the species’ behavioural characteristics,
or how it interacts with the environment. Underlying the physical and behavioural
features are the genetic characteristics of the species. This information can often
guide species conservation and recovery. The eastern massasauga rattlesnake
possesses unique physical, behavioural, and genetic characteristics.
PHYSICAL APPEARANCE (MORPHOLOGY)
THE GENERAL LOOK
The eastern massasauga rattlesnake (Sistrurus catenatus catenatus)
is Ontario’s only rattlesnake. The massasauga usually has a brown
rattle, with varying numbers of segments, at the end of its blunt tail.
The rattle can be a key feature in identifying the snake, unless the
rattle has broken off or the snake is young, in which case only a small
button may be visible. Massasaugas range in size from 47 to 76 cm.
The eastern massasauga rattlesnake.
The eastern hognose snake.
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The massasauga’s body is stout, in contrast to most of Ontario’s
snakes, which are quite slender. Only the adult eastern hognose
snake (Heterodon platyrhinos) has a similar form to that of the
massasauga. The ratttlesnake’s head is relatively wide, with a
white stripe and three black stripes extending back from the face
toward the neck.
A close-up of the massasauga’s unique head pattern,
vertical pupils and heat sensitive pits.
The heat sensitive pits between the eyes and the nostrils are unique to
the massasauga. Its vertical, cat-like pupils of the eyes open in dim
light to improve the snake’s night vision.
The typical pattern of the massasauga consists of dark brown blotches
on the back and three rows of alternating blotches on the side over a
grey background.
The belly is black with small white to yellow markings.
Cryptic patterns and colouration serve to break up the shape of
a snake to better disguise it in vegetation, rocks, leaf litter,
and shadows.
The massasauga can remain undetected with the help
of its pattern, even at close range.
THE REMARKABLE RATTLE
Rattlesnakes are born with a single small “button” and not a full rattle. Each time
rattlesnakes shed their skin, an additional segment is added to this button. The
rattle varies considerably in size and can be damaged or lost completely due to
wear and tear. The rattle is a remarkable evolutionary adaptation, allowing the
snake to warn others of its presence.
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The rattle is comprised of enlarged scales that loosely
interlock over one another. Each time the snake sheds
its skin, a new segment is added to the rattle.
This is a photo of a rattlesnakes rattle intact.
Rattlesnakes have a unique “tailshaker muscle.” When it contracts, this muscle
uses very little energy, allowing the snake to shake its tail rapidly.
An eastern massasauga rattlesnake, depending on the individual and its environment, may not rattle when in the presence of people or predators. Instead, it may
remain motionless and rely on its concealing colouration to stay hidden.
The rattle is only a warning to stay away, not an indication that the snake is prepared
to bite. Snakes would rather be left alone than interact with a predator or a human.
For more snake-friendly tips, see Section 4.
Occasionally a massasauga is found with the
entire rattle broken off.
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Eastern massasauga rattlesnakes are born with a single
cream-yellow coloured segment at the end of the
tail called a “button.” Each time the snake sheds its skin,
a new segment is added, creating the rattle. As the rattle grows
longer it becomes worn and several segments break off.
SNAKE SKIN – THREE L AYERS OF PROTECTION
First Layer, thin, clear
The first and clear outer layer of skin is shed (molted) as the
snake grows.
Second Keratinized
Layer, rough
The second layer is composed of many overlapping, protective
“keeled” scales.
The third layer of skin is thick and contains the pigment that gives the
snake its pattern.
Prior to shedding, the snake will look very dull or grey due to a milky
liquid between the old and new layers of skin. This appearance is most
noticeable as a grey or whitish colour in the spectacle scales that cover the eyes.
The snake will begin shedding by rubbing its head against hard objects until the
dead skin splits. As the snake moves, the skin is gradually peeled from the body.
The old skin will be left behind after shedding. Once the shedding process has
finished, the snake will appear shiny and clean. Massasaugas may shed their
skin one to three times yearly, depending on various factors affecting their growth
(age, food availability, and temperature).
Third Basil Layer,
thickest pigmented
A keeled scale is one that has a raised ridge along the scale’s mid-line, giving
the snake a rough or textured appearance.
smooth scales
keeled scales
Snakes often begin to shed their skin by rubbing their
face against a hard surface. As the snake moves along
the ground or hard object, the skin will be pulled off.
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Massasaugas can be recognized by the individual
pattern that is visible even on a shed skin. Toronto
Zoo identifies their snakes by taping the head
area of the shed skin to an identification card.
Snake skin is not wet or slimy but rather dry, and in the case of the
massasauga, quite coarse. The shed skin will show the texture of
the snake’s scales.
If you look closely at a snake’s shed skin, you may see the large, clear
scale (spectacle) that once covered the eye. Since snakes can’t close
their eyes, spectacles offer the snake protection while acting as its
eyelids. The milky liquid produced prior to shedding clouds the eyes
and impairs the snake’s vision. During this period, many snakes seek
seclusion, since they are vulnerable to predation or injury until molting is complete
and eyesight returns to normal.
A HEAT SENSING PIT
The eastern massasauga rattlesnake belongs to the pit viper (Viperidae) family. The
name refers to the small heat-sensitive facial pit (small opening) on either side of the
face, between the eye and nostril.
The pits are used to find warm-blooded prey through a large and highly sensitive
network of nerve endings. The brain interprets the information gathered by the two
pits to create an image of the prey animal.
Within 60 cm, a rattlesnake can find the exact location of a warm-blooded prey
species, even in complete darkness.
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Overhead view of eastern massasauga
rattlesnake’s relatively wide head.
Side-view of eastern massasauga rattlesnake’s head,
showing heat sensitive pit between eye and nostril.
Nostril
Facial pit
Worldwide, there are approximately 290 species in the pit viper family, but only
three occur in Canada:
• northern pacific rattlesnake (Crotalus viridis oreganus) from south-central
British Columbia;
• prairie rattlesnake (Crotalus viridis viridis) from southeastern Alberta and
southwestern Saskatchewan;
• eastern massasauga rattlesnake (Sistrurus catenatus catenatus) from Ontario.
A second pit viper was once present in Ontario, the timber rattlesnake (Crotalus
horridus). Habitat loss and human persecution are thought to have caused its
extirpation from Ontario. The last known sighting is from 1941 near Niagara. This
species is now only present in the U.S., where it is in decline.
THE FORKED TONGUE
The eastern massasauga rattlesnake possesses a long, slender and forked tongue
which, when not extended, is housed within a sheath inside the snake’s mouth.
With a flick of its tongue, the snake gathers information about its surroundings.
Sampling the air allows the snake to retrieve scent molecules, which it then
transfers to its “vomero-nasal organ” (Jacobson’s organ), located in the roof of its
mouth. By interpreting the information gathered by the nerves within this organ,
the snake learns about its surroundings.
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The long, forked tongue of the massasauga collects
scent molecules from the air when extended.
The molecules are then delivered by the
tongue to the “vomero-nasal organ” which
interprets the information received.
A snake may flick its tongue more frequently to sample the air in order to:
• explore new surroundings;
• locate special features of their home range;
• seek a suitable mate;
• confirm the presence of prey;
• determine if a predator or human is near.
A snake’s tongue is harmless and serves the snake only as a sensory device.
SENSING VIBRATIONS
A snake has neither an external ear opening nor a tympanum (exposed ear drum).
Rather, it feels vibrations, which travel along the snake’s jawbone and are processed
through an internal ear within the snake’s head.
TOUCH
Snakes, although covered in tough scales, are very sensitive to touch and certainly
feel pain.
VENOM
The massasauga’s venom consists of toxic proteins and digestive enzymes that kill
prey and begin to break down the tissue for easy digestion. The venom is produced in
glands located within each side of the snake’s head. During envenomation, the
venom travels from the glands into small delivery ducts and through the fangs into
the prey animal.
Venom is produced and stored in the glands of a snake, and must be injected. When
an animal is poisonous the poison is distributed through its body and cannot be
injected into another species. Poisonous animals are not edible, whereas a
venomous animal can be eaten if you avoid the glands containing the venom. The
eastern massasauga rattlesnake is venomous.
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Scientists consider the eastern massasauga rattlesnake capable of controlling both
the depth of its bite and the amount of venom it injects into the prey animal. This skill
is apparent from the fact that the snake may make a defensive strike without using
its venom. This “dry bite” may occur in 25% of defensive strikes.
The venom of the rattlesnake serves two main purposes. The
first is to kill prey, mainly small rodents. The second is to begin a
preliminary breakdown of the animal’s tissue for easier digestion.
Venom does not pose a threat to the snake itself. It is stored in
special glands and is carefully released through non-absorbent
ducts. Also, venom is produced and stored in an inert or inactive
enzymatic form.
Open mouth diagram of rattlesnake showing
venom glands, ducts, and fangs.
BEHAVIOURAL CHARACTERISTICS
The eastern massasauga rattlesnake is a fascinating creature. It uses its special
morphological features to sense prey, feed, attempt to avoid predation, and
survive in our harsh climate.
FEEDING FACTS
• Snakes subdue small prey by delivering venom through specialized,
elongated, hollow teeth known as fangs;
• The snake can move each fang separately. The fangs are similar to a
hypodermic needle. When not in use the fangs lie flat on the inside of
the mouth;
• During a strike the fangs pivot forward to gain contact with the
desired target, usually a vole or a mouse. After a strike is made the
snake instantly releases its fangs and waits for the animal to stop
moving before attempting to swallow it. This bite and release
ensures that a fighting animal will not injure the snake through a bite
or a scratch;
• Though the mouse or vole may escape it will die soon afterward;
• Since snakes are not able to chew their food, they swallow the
animal whole, usually head first. This is a relatively slow process
depending on the size of the prey. Depending on the ambient
temperature, most food is usually totally digested within a week;
Illustration of hollow fang used to
deliver venom to prey.
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• overlapping scales on the snake’s body will expand to accommodate larger prey;
• Such adaptations enable the snake to consume a larger meal, and in turn, allow a
longer period of time before the next feeding. Rattlesnakes may survive on less
than 12 meals per season.
It is thought that pit vipers may be the most evolved of the snakes because of these
adaptations.
Eastern massasauga rattlesnake about to strike.
During the strike the fangs pivot forward.
TEMPERATURE CONTROL
Snakes have the unique ability to regulate their body temperature using the
surrounding environment. Since a snake’s body heat is obtained from its environment, and not from metabolizing food energy, reptiles do not need to eat to keep
their bodies warm. It is by this method that a massasauga can live on so few meals
each year. Over the winter, the snake may not eat at all for six months.
REPTILES AND AMPHIBIANS (ECTOTHERMIC)
• Snakes are “ectothermic.” “Ecto” means from the outside and “thermic” means
temperature.
• In order to increase, maintain or lower body temperature, snakes utilize the heat or
cold from “outside” of their body (in the surrounding environment).
• Ectotherms (such as snakes) become sluggish, and their metabolic rates lower, as
the temperature falls. Although massasaugas are capable of limited movement at
4˚C, they require warmer temperatures for activity.
• Rattlesnake species do not generally become active until temperatures exceed
12-13˚C and their body temperature reaches a range of between 25 and 30˚C.
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MAMMALS AND BIRDS (ENDOTHERMIC)
• Mammals and birds create most of their own body heat, and are referred to as
“endothermic.” “Endo” means from the inside and “thermic” means temperature.
• Mammals use 90% of their food energy to regulate their body temperature.
• Although some mammals and birds can live in cold conditions, they need much
more food than reptiles to keep warm and stay alive.
Both endotherms and ectotherms need to maintain a preferred body temperature
for at least their active periods of the year – they just do it differently.
In order to carry out everyday activities and bodily functions, the body temperature of
a snake must rise to an acceptable range. Through “behavioural thermo-regulation,”
a snake changes or maintains body temperature by varying its exposure to the
sun, shade, or shelter. In turn, the snake attains temperature levels suitable for
feeding, digestion, reproduction and, for females, incubation of internally
developing embryos. Thermo-regulation is also influenced by subtle changes in
position while under cover. When it is too cold to thermoregulate, snakes seek
shelter, reduce their activity and lower their energy requirements by reducing body
temperature and metabolism.
Suitable areas for thermo-regulation contain
both open areas and cover.
Reptiles raise their body temperature by
basking in open sunny areas.
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Vegetation and leaf litter are suitable cover, while
rock crevices can provide more stable shelter
from the elements.
Snake in sheltered area.
Snakes demonstrate a preference for specific basking locations, where they
increase their body temperature. At certain times of the year, they will often frequent
the same area. A snake may move over large distances to find these important
and preferred habitats. A snake will use an arrangement of different habitats as it
moves about its home range seeking new sources of food or mates.
Snakes have a “thermal maximum,” or a body temperature they should not
exceed. If the snake is unable to cool down, a loss of motor-skills or even
death may occur.
MATING AND YOUNG -GESTATION
The eastern massasauga rattlesnake produces young every two to
three years. Because of the short activity period during which snakes
in Ontario feed (May to September), it may take two to three years
between breeding events for the female snake to store enough fat
energy to support developing embryos. In any given year, two-thirds of
the population may not produce young!
Most eastern massasauga rattlesnakes in Ontario mate from midJune to August. The male will use his tongue to pick up and follow the
females scent trail and initiate courting behaviour before actual
copulation. Ritualized combat between males may occur, with the
victor mating the female.
The gravid (pregnant) female will stay at a “gestation site” during part
of the summer. This is a “micro-habitat” within the snake’s habitat.
The gestation site grants female rattlesnakes cover and easy access
to a wide range of temperatures in order to incubate the young developing within their body.
Males involved in ritualized combat. These
disputes end with the strongest or biggest
snake mating the female.
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Massasaugas mating: the male’s hemipenes have
been inserted into the female’s cloaca. The
cloaca is the opening for the snakes’s digestive
and reproductive system.
The hemipenes are a male snake’s sex organ. During
copulation, the organ is inserted into the females
cloaca. The everted hemipenes are visible in the photo.
An example of one type of gestation site
along Georgian Bay.
A gravid female basking, showing the
increased body size.
Although some snakes do lay eggs, pit vipers such as the massasauga
are “ovoviviparous,” the young are delivered live after hatching from
internal membranous (thin tissue) eggs. This process is known as
parturition. Six to twenty young, approximately 20 cm long, are born in
late July or August. Newly born snakes may remain beneath the
protective cover at the birthing site for four or five days.
The young are on their own, receiving no assistance from the adults, as
they begin their life in the wild.
A female rattlesnake gives birth in an
exhibit at the Toronto Zoo.
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Female massasauga with young soon after parturition.
Neonate with yellow-cream “button” at
the end of its tail.
At birth, eastern massasauga rattlesnakes are already venomous and have the
ability to strike prey. These young snakes are small versions of their parents
but lack a full rattle.
THREATS TO GESTATION SITES
The eastern massasauga rattlesnake is negatively affected by the destruction of
gestation sites. These sites are crucial, since Ontario’s, short summers make it
difficult for gravid females on their own to maintain the warm, relatively constant
body temperatures needed for their young to develop successfully. Since female
rattlesnakes often return to the same site, and since many individuals often use one
site, the destruction of a single gestation site could impair the reproductive success
of several females. This occurrence could, in turn, affect the viability of an entire
population. Fortunately, gestation sites are readily identifiable, and so people can
take steps to prevent them from being destroyed.
HIBERNATION
Hibernation is the only way that the eastern massasauga rattlesnake can survive in
a cold climate. Cooler weather, and shorter days, act as cues for massasaugas to
start a seasonal migration. This migration is usually less than 1 km, as the snakes
move from their summer areas back to traditional hibernation sites. Such sites may
be found in wet low-lying areas, swampy peatlands, dry woodlands, or rocky areas.
As with all reptiles, cold temperatures prevent snakes from regular activity and
proper digestion. They remain inactive during the winter, while fat stores
accumulated during the summer satisfy their limited energy requirements.
In the hibernaculum, the snake is protected from freezing temperatures until spring
arrives. A hibernaculum is a cavity or burrow such as rock fissures, holes along tree
roots, and crayfish or animal burrows that have access to high humidity or underground water. As the snake prepares for the long, cold winter its heart rate slows,
causing a decreased intake of oxygen and an inability to feed for the entire winter.
Although respiration and metabolism will become slow or may temporarily halt, the
snake is neither sleeping nor deceased.
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Hibernation sites are found within different habitats
throughout the four regions where massasauga
still occur in Ontario.
A small animal burrow provides access
to an underground opening in the
bedrock near Georgian Bay.
For over-wintering, the massasauga may use
crayfish burrows, such as this one, as well as
mammal burrows, rock fissures, and other
openings which extend below the frost line.
Trees may indicate a fissure in the underlying
bedrock around Georgian Bay. These openings
may provide a suitable hibernaculum
(over-wintering den) in local areas.
The massasauga will bask near the hibernaculum until daily temperatures become
too cold to warrant continued exposure, usually late October to early November. At
that time, the snake will settle within the hibernaculum until consistently warm days
occur again in April. Though the snake is cold, it can move further down into the den
as the winter frost sinks lower into the ground.
Deep snow over the hibernaculum provides additional protection from the frost.
Although some species of snakes hibernate communally (two or more snakes per
hibernaculum), massasaugas usually prefer a solitary hibernation.
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THREATS TO THE HIBERNACULUM
Deep snow can serve to insulate the
hibernacula during the winter months.
The hibernacula are not easy to identify, and are susceptible to inadvertent destruction in the course of development projects. Hibernation
sites may be destroyed by excavation, burial, or flooding. Since eastern
massasauga rattlesnakes typically hibernate in water-saturated soils,
hibernation sites may also be adversely affected by drainage. However,
too little is known about the physical conditions within rattlesnake
hibernacula to predict how development might affect a site’s integrity.
Conceivably, even the removal of several trees could sufficiently alter
local soil moisture conditions to affect nearby hibernacula.
The destruction of hibernation sites in the winter would obviously result in the death
of its occupants. However, because the snakes use the sites repeatedly (known as
site fidelity), individuals whose over-wintering sites are destroyed during the
summer (when the site is not occupied) would also be likely to suffer mortality.
Scientists suspect that massasaugas will search for their destroyed hibernaculum
even to the point of being killed by cold temperatures.
EMERGENCE
As spring approaches, the air and ground surrounding the outside of the hibernaculum begins to warm. This temperature increase will slowly cause the inside of the
chamber to warm, usually in late April. The snake will slowly move closer to the
entrance as the days continue to get warmer. The snake’s metabolism will increase
and, in turn, alertness, heart rate, and intake of oxygen will return to normal. As
a precaution, massasaugas remain near the hibernaculum to bask, until the
threat of snow or cold weather is eliminated. In May, the snake moves back to its
summer habitat.
GENETIC DIVERSITY
For several years, researchers have been collecting blood samples from eastern
massasauga rattlesnakes in order to gain knowledge about the species’ genetic
diversity and population structure.
To date, the research has revealed that a great deal of structure exists between the
populations and sub-populations: neighbouring populations are quite distinct from
one another. Scientists have not yet discovered the cause of this peculiarity. The
massasauga has a high degree of site fidelity, returning to the same hibernaculum
and gestation sites. They are also sit-and-wait predators. This combination of traits
makes their home range requirements smaller and lessens the need to disperse
great distances. As a result, genetic mixing may be limited.
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