|Can you imagine a kangaroo in your backyard, even if you though don’t live in Australia or New Guinea? Kangaroos have recently hopped over seas to the United States. In 2000, CNN reports “Kangaroo Horde Makes itself at Home, in Georgia.” Kangaroos are the main attraction in Dawsonville, a small Georgia town sixty miles from Atlanta. This is the largest collection of kangaroos outside Australia. Debbie and Roger Nelson run the Kangaroo Conservation Center along with a team of biologists and other workers. This Center is open to visitors, as well. One of the visitors, Stephen Prozak, states, “Just watching them work, watching them move, watching them eat, watching them deal with everyday things up close is fascinating” (George, 2000). So, what makes the kangaroo so fascinating?
One of the first fascinations is how the kangaroo got its name. The kangaroo got its common name from the European explorers. The explorers asked an aborigine, a native Australian, what these strange hopping animals were called. The aborigine replied, “Kangaroo,” which meant, “I don’t understand” your question. The European explorers thought this was the animal’s name. (Kangaroo, 1997)
This was the start of the kangaroo’s common name; on the other hand, scientists identified and classified the kangaroo according to special rules. This process gave the kangaroo its taxonomy. The taxonomy of the kangaroo is as follows: Kingdom Animalia, Phylum Chordata, Subphylum Gnathostomata, Class Mammalia, Subclass Marsupialia, Order Diprotodontia, Family Macropodidae, Genus Macropus, Species many. The species is not listed because there is over forty different types of kangaroos.
Almost all native mammals in Australia are marsupials. The female mammals all have external pouches in which their young develop. The females carry and feed the young with milk until the are able to survive on their own. They also developed extraordinary speed and a water-conserving physiology. These are common traits of the marsupials, but what makes a kangaroo, a kangaroo? Let’s begin with the structure.
Organisms that are commonly referred to as “kangaroos” generally comprise two families, Macropodidae and Potoroidae (Domico, 1993). These families include both kangaroos and kangaroo rats, including sixty species in sixteen genera (Kangaroos and Wallabies, 1984). Because of this species diversity, many physical characteristics of kangaroos vary widely. Body size is no exception to this rule. One of the “classic” kangaroos is the Red kangaroo. Red kangaroos average sixty-five inches from head to tail in body length (Ganslosser, 1990). While the average length of a Red kangaroo is sixty-five inches, kangaroos in general exhibit great sexual dimorphism in body size, and males can be up to twice the size of their female counterparts (Kangaroos and Wallabies, 1984). Along with their great size comes great weight. Red kangaroo males can weigh up to two hundred pounds (Ganslosser, 1990). One of the reasons that kangaroos can reach such large masses is that kangaroos exhibit continued growth after maturity (Ganslosser, 1990).
Coat Type and Differences
Coat type and color are another one of the features that can differentiate separate species of kangaroos. Although coat color and type can differ from one species to the next, kangaroo fur is almost always very dense (Grzimek, 1972). As with size, sexual dimorphism is also expressed though differences in coat color. For example, Red kangaroo males exhibit the classic reddish colored coats. Female Red kangaroos on the other hand, have coats that are bluish- gray in color (Kangaroos and Wallabies, 1984).
The kangaroo coat also serves a very important purpose in the regulation of body temperature. Because of dense fur and environmental conditions, kangaroos have adaptive cooling mechanisms. The first of these mechanisms is panting, similar to that of a dog (Grzimek, 1972). Kangaroos also reduce their body temperature by licking their forearms. This is especially efficient because kangaroos have a “dense network of fine blood vessels very close to the surface of their forearms” (Thwaites, 1997). Licking their forearms aids the evaporation and keeps their body temperatures constant.
The main features of the kangaroo skeleton are its four limbs, two forelimbs and two hind limbs. The limbs of the kangaroo also contribute to its upright posture (Grzimek, 1972). The kangaroo have two front limbs. The forelimbs are heavily clawed and short in comparison to the kangaroos’ hind limbs (Grzimek, 1972). The main functions of the forelimbs are two pick up food and transport it to its mouth (Bertin, 1967). One of the less necessary functions of the forelimbs is their function on playing and fighting with other kangaroos. The hind limbs of the kangaroo show great contrast to the forelimbs. Whereas the forelimbs are short and heavily clawed, the hind limbs are long and powerful (Grzimek, 1972). The hind limbs terminate at the hind feet, which too serve enormous function in kangaroo mobility. The family that kangaroos are in is Macropodidae which translates into “large footed” (Kangaroos and Wallabies, 1984). The kangaroo hind foot typically has between four and five unique digits. The first digit is missing in all but the genera Hysiprymnodon. The second and the third digits of the kangaroo hind foot are “united by skin”, while the fourth and fifth digits are considerably longer than the first three. The fourth digit features a prominent long nail that can be used for grooming purposes (Grzimek, 1972).
The tail of the kangaroo is often times referred to as its “third leg” which seems fitting considering its increased function when compared to tails of other organisms. The kangaroo tail is both long and strong. The average length of the tail in the Red kangaroo is 42 inches (Kangaroos and Wallabies 1984). When you compare that to the fact that the average Red kangaroo is only 65 inches (Ganslosser, 1990), the tail importance becomes clearer. One of the reasons that the tail has great functional value to the kangaroo is because of its size. Kangaroos frequently use their tails as a third leg to create a tripod when at rest, as well as using it for a counter-balance while in motion (Bertin, 1967).
The senses of the kangaroo are another part of their anatomy that is crucial to their survival. Kangaroos have two large eyes which are situated on both sides of their head. Their location provides for a wide field of vision which helps kangaroos avoid predation (Domico, 1993). The ears of the kangaroo are its source for hearing. The ears of a kangaroo are typically round or oval shaped and long which aids in the collection of sound (Grzimek, 1972). This sound collection can be vital against predation because kangaroos are nocturnal. Smell is another one of the important kangaroo senses. Kangaroos typically have a short snout. The coloration of the snout and the muzzle can also differentiate separate species. For example, the Red kangaroo has a black and white patch at the side, where in Grey kangaroo only the “margin of the nostrils are bare black skin” (Kangaroos, 2002). The structure of this snout and its ability to smell becomes vital during the kangaroos' travel to the pouch after birth.
Possibly the most distinguishing traits of the kangaroo have to do with their reproductive system. Probably the most identifiably feature of the kangaroo is its pouch. However, contrary to popular belief, and even popular science until recently, kangaroos are not born in the pouch of their mother. Baby kangaroos grow and develop initially inside one of the uteruses of their mother. Marsupials are unique in that all females have two uteruses joined at the vagina (Domico, 1993). Young are delivered through a central canal in the female’s reproductive system. This birth canal forms before the first birth of a female and it’s usually permanent thereafter (Ganslosser, 1990). After delivery from the uterus the baby kangaroo, or joey, relies on its senses to guide it to the pouch. The pouch opens to the front and inside the pouch there are four nipples of which two produce milk (Grzimek, 1972). The pouch is warm and fur free with a temperature of ninety degrees Fahrenheit (Domico, 1993). The pouch provides a growth environment where the joey will remain until maturity.
Dentition and Digestion
The dentition of the kangaroo reflects its functional purpose as an herbivorous animal. The dental formula for kangaroos is i3, c 0-1/0, pm 2/2, m 4/4 (Nowak, 1991). Dental formulas tell how many of each kind of tooth are present in a species. The kangaroo dentition contains three incisors in each half of the mouth (i3), either zero or one canine (c 0-1/0), four premolars (pm 2/2), and eight molars (m 4/4). To find the total number of teeth, double the number of teeth present in the dental formula. Kangaroos typically have between 32 and 34 teeth, which can vary depending on the presence of premolars and the number of permanent molars (Grzimek 1972). The first teeth in the dental formula are the incisors. Incisors are commonly used pincers and over time have been modified to resemble chisels (Myers, 1997). Incisors are present in both the upper and lower jaw of the kangaroo. The lower incisors are both forward projecting and chisel-like (Grzimek, 1972). Contrary to incisors, canines are frequently absent from the kangaroo dentition, with the lower canines being almost always absent. Canines are typically used to grab and hold prey (Myers, 1997). Since kangaroos are herbivores, they seldom have use for them. Molars are the last class of teeth in the dental formula of the kangaroo, including both premolars and permanent ones. The kangaroo can have between 4-7 permanent molars. These permanent molars migrate forward when the 1-2 premolars on the top and bottom of the jaw fall out prematurely (Grzimek, 1972).
While in captivity kangaroos are often seen to exhibit a type of body lurching. This is actually an important step in the kangaroo digestion process. The stomach of the kangaroo is large and sacculated, consisting of several jointed cavities (Kangaroos and Wallabies, 1984). The process of digestion on the kangaroo begins with the initial chewing and swallowing of the food. However, kangaroos unlike humans regurgitate, re-chew, and then re-swallow their food (Ganslosser, 1990). This leads to the lurching motion that observers often see in captive kangaroos.
Kangaroos are herbivores. They are grazers that generally feed on grasses, plants, and shrubbery. The Red Kangaroo prefers young, green grasses and herbs. Kangaroos specialize in selecting greener, moister vegetation that has a relatively low nitrogen content. Due to the fact that kangaroos eat moist vegetation, they only need to drink once a week. This is adequate for their nutritional needs because kangaroos need a lot less water than other animals such as livestock. (Dawson, 1995)
Kangaroos usually feed on the fringes of forests, in open woodlands, and near natural or improved pastures. They prefer to eat from dusk until dawn under the cover of darkness to protect them from any danger. (MacDonald, 1984)
With kangaroos, mating occurs when the female is in estrus, or heat. The male’s goal in mating is to mate with as many females as possible. For most kangaroos, especially the Grey Kangaroo, there is a dominance hierarchy in effect. All of the mating rights are given to a single dominant male who is determined by size and strength. The dominant male is usually only replaced when he dies; however, he may be beaten out by a rival kangaroo during a fight. Some males are still able to mate without the dominant male’s knowledge. This helps keep the same traits from being passed to all the offspring. When the male is courting the female, he will follow her around, sniffing her to find out if she is ready to mate. Some common mating behaviors include the male stroking the female’s chest, tail, or neck, and the male bobbing his head around and making a clucking sound. When the female is ready, the pair will mate.
Mating takes place with both the male and female standing with their feet on the ground. It can last anywhere from two minutes to fifty minutes, depending on the species. (Domico, 1993)
There are no exterior signs to show that a female kangaroo is pregnant. Adult female kangaroos are constantly pregnant. They average two to three young per year, if the conditions, such as climate and food supply, are favorable. The gestation period of the kangaroo is anywhere from 21 to 38 days. The average length of gestation is 32 days. It is uncommon for a female to give birth to more than one young at a time. When a kangaroo is born, it is referred to as a joey. A joey can be either male or female. At birth the joey is deaf, blind, and completely naked. It is about the size of a small bean and only weighs about ¾ of a gram. Despite these things, the joey’s forearms and hands are very well developed and ready for their first mission in life. (Ganslosser, 1990)
Immediately after birth the joey begins the first major journey in life - the climb to the pouch. The joey must find a way up the mother’s belly and into the pouch using only the sense of smell. This happens about 10 to 15 seconds after birth. The journey only lasts 2 to 3 minutes and is only about 6 to 7 inches in length, but is vital to the survival of the young joey. (Domico, 1993)
Once the joey is inside the pouch, it attaches to one of four teats. It attaches so tightly that it cannot be removed without causing harm to the joey’s mouth. (Ganslosser, 1990) The joey will live in the pouch anywhere from 90 days in the smaller species to 300 days in the larger species. While in the pouch the joey grows very rapidly. The joey can release the teat at 70 days. By the time the joey is 130 days old, it can open its eyes. The kangaroo can get out of the pouch at about 6 ½ months but still spends a lot of time in the pouch. This allows the joey to explore life out of the pouch but still have the comfort of returning to the pouch. At eight months the joey is kicked out of the pouch for good to make room for a new joey. The joey is still allowed to nurse from a teat with a special milk formula for an older joey. The more a joey grows, the richer the milk gets. This explains why the mother kangaroo has four teats in her pouch. Each teat has specially formulated milk for the joeys at different stages of their lives. The mother kangaroo can have up to three joeys at a time due to the fact that she will mate one to two days after giving birth. After mating, the newly conceived baby will stay dormant until the pouch is available. This new young is called a dormant embryo. This dormant baby also ensures that there is always a young baby on hand in case of death. Besides this dormant embryo, she will also have a newly born pouch young and a still nursing young at foot. A joey is fully grown at 18 months. (Domico, 1993)
Adult kangaroos can live to be 30 years old. They are still able to breed into their twenties. Most joeys will survive until adulthood, but only after a sequence of rainy years, which provides adequate food. In moderate conditions, most do not survive past weaning and in very dry years most die before entering the pouch due to lack of nutrition of both mother and joey. (MacDonald, 1984)
Interaction between Species
Kangaroos have become increasingly social due compared to in the past due to their increased size and greater mobility. Another reason they have become more social is that they are doing more activities in the daytime and eating in a more open habitat. They are usually found in clusters of 2 to 10 individuals. They live in semi-nomadic groups called mobs. A mob can consist of several hundred kangaroos. This increased sociability allows them to watch out for possible predators. Kangaroos also share common home ranges, although males typically have a larger home range than females do.
One specific type of kangaroo interaction is fighting. Fighting most commonly takes the form of wrestling. The animals support themselves on their hind legs and tail, wrap their arms around one another and try to knock each other over. In the larger species, only the males fight and they do not bite or scratch. This fighting is a ritual and has well-established rules. Kicking is done by the ultimate loser, especially when he cannot break free from his opponent. The fight consists of several minutes of rounds with rest periods in between each round. The rest period ends when one kangaroo stands fully erect again, initiating the next round of fighting. (Ganslosser, 1990)
Natural History and Ecology
Approximately 65 to 135 million years ago, the continents on Earth were all conjoined together to form one large land mass called Pangaea. During that time, there were very high ocean levels, which lead to high elevation. From this, tropical islands were created (Nowak, 1991). About eight million years ago, the continent of Australia experienced dramatic climate changes. The climate became cool and dry. This type of climate change led to the center of the continent to dry out. Rainforests became grasslands and woodland areas (Domico, 1993). As Australia was drifting further apart from Pangaea, the country of New Guinea was separating from Australia. They are now separated by the Torres Strait. When the sea level fell, there was a dry-land connection.
Starting around 30 million years ago, rat-sized creatures that lived on the tops of trees, leapt down from the safety of trees. They evolved into modern day kangaroos. These creatures inhabited rocky hills, forests, and open country (Duplaix, 1983).
The Kangaroo Environment
Kangaroos were first sighted by Europeans as early as 1605 A.D. (Domico, 1993). When the European explorers came to Australia, they saw kangaroos, which were a foreign animal to them. They asked the Aborigines what these abnormal creatures are and they replied, “Kangaroo”, which in the Aborigine language means “I don’t know” (Domico, 1993).
Currently, there are many different types of kangaroos which depending upon the different species, determines where they are found. However, all forms of kangaroos are found mostly on Australia and surrounding countries such as New Zealand, Tasmania, and New Guinea. The red kangaroo is found in dry conditions in central Australia. Red kangaroos are also found in grasslands, shrub lands, and scrublands. These types of kangaroos prefer open plains where trees and bushes are abundant, which means that they are not usually found in regions without shade (Nowak, 1991). Red kangaroos are also found in the desert where the rainfall average is less than 500 millimeters.
Due to the types of kangaroos and limitations on resources, the habitat of a Gray Kangaroo is incredibly different than the red kangaroo. Gray Kangaroos tend to live in the southwest regions of Australia. They favor dense scrub found in open forests and woodlands. The Tree Kangaroo, which is not abundant as much as the red and gray kangaroo, are found in trees. Larger kangaroos can be found on the continent of Africa. Here, kangaroos occupy the same niche as antelopes (Nowak, 1991). Once predators, such as humans, disturb kangaroos they may settle into a new region several miles away.
Over the years, kangaroos have developed special adaptations. They have the ability to hop 15-25 miles per hour for several miles. While hoping in short distances, they are able to get up to 40 miles per hour. This allows them to outrun predators and use resources in a large area because they are capable to cover large distances rapidly. Kangaroos are also able to increase their length of jump instead of moving their legs faster.
While kangaroos increase their speed, they do not to increase their intake of oxygen. No energy is consumed from one jump to the next because the legs of a kangaroo stretch to absorb shock and automatically contracts for the next jump (Dawson, 1995).
When kangaroos cool down after an extensive run, they usually pant. They save water because their dense, reflective fur insulates their body from heat coming in from the outside. During the rest of the panting process, they adjust the rate of evaporation by varying airflow in through the nostrils (Dawson, 1995).
Not only do kangaroos pant after running long distances, they also sweat. Kangaroos only sweat when exerting themselves. They are able to stop sweating the instant they stop exercising (Dawson, 1995). Kangaroos have the ability to switch off sweating back to panting. This special adaptation permits them to conserve more water. Kangaroos can drop fluid from their mouth and nasal glands on to their forearms. They spread this fluid by wiping and licking, which helps to regulate their body temperature. This is extremely helpful in temperatures that can get up to 140 degrees Fahrenheit.
Kangaroos and the Future
Over the past few decades, Australia has been trying to control the population of the kangaroo because there are a lot of overrunning pastures and croplands. According to Australia’s Federal Department, they reported back in 1997 that there were over 19 million kangaroos. The population of kangaroos is done through the Quota System to prevent over harvesting. Each state in Australia estimates the numbers of kangaroos from aerial and ground surveys. They also look for the different types of species, their sizes, and sex ratios of kangaroos that have recently been shot and also local seasonal conditions (Domico, 2000). Zones where kangaroos have very high populations, they have higher quotas; although, in every zone, the overall population is kept in mind.
Some opponents of the quota system claim that the quotas are too high. Back in 1975, more than one million kangaroos were legally available to harvest. The number increased dramatically to 3 million in 1981, all the way up to 5.7 million in 1999 (Domico, 2000). The organization of Greenpeace believes that if this continues, this would undeniably lead to kangaroo extinction (Domico, 2000). Although Greenpeace does not agree with this decision, the United Grazier’s Association of Queensland and the National Farmers’ Federation insist that if kangaroos are not being hunted, the population will increase dramatically and many farmers would lose a great deal of their crops and wouldn’t be able to survive (Domico, 2000).
Over the last thirty years, the population has been increasing little by little; however, the population is trying to be controlled by hunting for their meat and skin. Weather has also been a factor in population control. Droughts play a huge factor because if there is no rainfall, plants are not able to flourish, which then leads to limited resources. When droughts do occur, the population does not increase (Domico, 1993).
At this time, Australia has allowed hunting to be done on kangaroos. Currently, there are only five species of large kangaroos that are considered fair game. Hunters focus mainly on red and gray kangaroos and also the common wallaroo. More than twenty million of the kangaroos that are targeted, these species are not in any danger of extinction (Domico, 1993).
Professional shooters are invited to shoot kangaroos on land that is heavily populated with them. The hunters then sell their skins to tanneries, and the meat is used for pet food and also taken to specialty meat markets for humans (Domico, 2000).
Another factor that is occurring that is limiting the population of kangaroos is the increase of vehicles that are intruding their environment. Road kill is a big deal that is significant to the mortality factor (Domico, 1993). In the state of Victoria, researchers have found that kangaroos that become road kill seem to peak during certain seasons around a full moon. The majority of the dead kangaroos were males (Domico, 1993). Australia has been putting up speed bumps to decrease the amount of kangaroos that are being killed.