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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. 10 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. 11 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. 12 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. 13 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. 14 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. 15 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. 16 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. 17 • 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. 18 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. 19 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. 20 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. 21 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. 22 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. 23 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. 24