Tammar Wallaby, Macropus eugenii
The tammar wallaby (Macropus eugenii), also known as the darma wallaby or dama wallaby, is a marsupial that can be found in western and southern areas of Australia. It has also been introduced into areas of Australia where it once lived and into New Zealand. It prefers a habitat within grassland areas.
The tammar wallaby was first discovered in 1817 by a French naturalist named Anselme Gaëtan Desmarest. He found the wallaby on Ile Eugene, an island off the coast of Southern Australia, and named it after this area. This island, now known as St. Peter Island, was originally named after Eugene Hamelin, the French commander of the ship Naturaliste. This species’ common name is derived from plants in which the species shelters, Allocasuarina campestris, which are locally known as tamma. Studies have shown that the island and mainland species may have diverged between seven thousand and fifteen thousand years ago. The tammar wallabies on Flinders Island were grey in color and slightly larger than the individuals found on West and East Wallabi Islands.
A study conducted in 1991 on the skulls of tammar wallabies from many areas showed that the species could be broken up into three groups. The first group contains populations from East and West Wallabi Islands, Middle Island, Garden Island, and western mainland areas of Australia. The second group contains populations from southern areas of mainland Australia, Flinders Island, and New Zealand. The third group only contains the population that can be found on Kangaroo Island. These groups have been listed as subspecies by the Western Australia Department of Environment and Conservation. The first group is known as M. e. derbianus, the second group M. e. eugenii, and the third is called M. e. decres.
The tammar wallaby displays a sexual dimorphism, with males growing larger than females. Males can reach an average body length between 23 and 27 inches and a weight of up to 20 pounds, while females reach a length between 20 and 25 inches and a weight of up to 15 pounds. The tail lengths vary in size depending upon the sex, reaching a length between 13 and 18 inches. It is one of the smallest wallaby species and has a small head with prominent ears. It is typically dark grey in color, with a lighter underbelly and reddish grey fur on the sides.
As is typical to members of its family, the tammar wallaby moves about by hopping, using its powerful hind legs to leap between 2.5 and 8 feet per stride. When an individual lands after a hop, the energy is converted into strain energy when the tendons stretch. This energy allows the wallaby to leap again, with almost as much force as the original hop, in a system known as elastic recoil. The amount of energy it uses to hop will increase with the speed and the weight that the individual is carrying. Mother tammar wallabies greatly benefit from this ability, because they can move around quickly without using large amounts of energy.
The tammar wallaby is able to distinguish between different shades of black and white in varying light conditions. It is thought to be able to see colors on the blue and green spectrum and distinguish between two monochromatic bands of color. Like a cat’s ears, the ears of the tammar wallaby are mobile and can detect noises without requiring movement of the head. Its sense of smell is advanced, even at birth, in order to locate food sources. The species is able to maintain a cool temperature by panting and licking under its forearms. If temperatures reach over 86 °F, the wallaby will have a more difficult time retaining water in its body and it cannot survive in areas where temperatures reach above 104 °F. In order to avoid dehydration, it reabsorbs water within the distal colon and urinates less. Its ability to concentrate urine allows them to drink seawater if fresh water is not available. Many species that are located on islands are able to survive completely on saltwater and the moisture consumed from vegetation.
The tammar wallaby is typically nocturnal and holds a winter home range of forty acres. In warmer months, the wallaby will live in a home range of up to one hundred acres. These ranges often overlap those of wallabies. Larger ranges occur when food is not abundant and individuals can spend a large amount of their time foraging.
Like all species of wallaby, the tammar wallaby is an herbivore. It remains in the protective shade of thick vegetation during the day and moves out to forage at dusk. It is known to graze and browse for food, but it is not adept at consuming food in a browsing manner. It will hold larger leaves in its forepaws and spends much of its foraging time chewing. It is thought that this helps it digest its food, but it is not typical of other wallaby species. Its diet consists of acacia seeds, Corymbia calophylla, Gastrolobium bilobum, and Austrodanthonia setacea.
The tammar wallaby has shown a varying amount resistance to a plant poison known as sodium fluoroacetate, depending upon a population’s location. Populations in mainland Australia have a higher tolerance for the poison than those on Kangaroo Island, and it is thought that populations in New Zealand have little resistance to the poison, as overpopulation has been controlled by using it. Populations of this species found on Garden Island and West and East Wallabi Islands are thought to have little resistance to sodium fluoroacetate, because these islands do not contain the plants in which the poison is found. However, they are thought to have a higher resistance than the tammar wallabies found on Kangaroo Island.
The tammar wallaby lives in stable groups that are thought to help protect against predation. However, if groups become too large, individuals will spend more time interacting, grooming, and foraging, which leaves open to predation. Common predators of this species include red foxes, dingos, wedge-tailed eagles, and feral cats. If a predator is near a group, the wallabies do not typically react to the noise caused by the animal, depending more upon the sense of smell and sight. If a predator is spotted, one wallaby will beat its foot on the ground, alerting the other members of the group to the danger. If a young wallaby is separated from the group, it will emit a loud screeching call, and females may reply with a similar sound.
The breeding season for the tammar wallaby occurs seasonally. Males will approach a female and sniff her pouch to determine if she is in estrous. Males will compete for females during the breeding season, so a hierarchy is created in order to aid in successful reproduction. Males will guard the females that they have chosen to breed with, and males that are more dominant in the hierarchy will breed with more females. The peak birthing season occurs between late January and early February. Joeys move into the mother’s pouch after birth, where they will suckle for 100 to 125 days. After this period, the joey will remain in the pouch, but will cease continuous suckling. At about 200 days of age, the joey will periodically leave pouch to feed on grass and return to suckle and to remain protected. At 250 days of age, the joey is mature enough to leave the pouch. It will remain with its mother for up to 350 days of age, after which time it has reached full maturity. Mothers can breed again shortly after giving birth.
The tammar wallaby is a model organism that is used in the study of mammal biology and marsupial biology. This species has been used in studies regarding metabolism, immunology, reproductive biology, and neurobiology among other studies. Individuals are easy and inexpensive to keep in captivity and are typically kept in outdoor enclosures with plenty of vegetation and water. If a group containing one male and at least five females are kept in a large enough area, breeding efforts can be very successful. Genetic studies of this species have resulted in its genome being fully sequenced, which was announced in 2011. It has been found that a compound in tammar wallaby milk, a protein known as AGG01, may provide a new and powerful type of antibiotic. Lab studies have shown that the protein is one hundred times stronger than penicillin, killing ninety-nine percent of the pathogenic bacteria that was present in its culture including Proteus vulgaris, Salmonella, and Staphylococcus aureus and a fungus species.
An ailment known as tammar sudden death syndrome struck captive tammar wallabies in Queensland and New South Wales in 1998. Between 120 and 130 wallabies perished less than twelve hours after displaying the first symptoms of the syndrome, although many individuals showed no symptoms. Examining the bodies of the wallabies after their deaths showed that the animals experienced hemorrhaging in the abdominal and thoracic organs and in the muscle tissues. The syndrome was found to be caused by a pathogen of the orbvirus family Reoviridae. It does not occur south of Sydney, Australia and seems to occur only in the summer months. Unfortunately, there is no cure due to the swift onset of the syndrome.
Habitat loss has been the main cause of the decrease in tammar wallaby populations since the European occupation of Australia. By the 20th century, the population was described as high in southwestern areas of Australia, but declining in the north, especially in areas where agriculture was thriving. Declines also occurred due to the introduction of sheep. In the 19th century, populations around Adelaide and in the Eyre Peninsula experienced a large decrease due to uncontrolled hunting by farmers in the 1920’s and 1970’s respectively. This type of hunting also negatively affected populations on Flinders and St. Peter Islands.
Colonial administrator Sir George Grey introduced the tammar wallaby onto New Zealand’s Kawau Island in 1870, and the species has since then become overpopulated in that area. One effort to control this population involved using the natural rodenticide sodium fluoroacetate, but this caused some debate due to the effects on non-targeted creatures, including humans. These wallabies were introduced onto the North Island of the Houtman Abrolhos island chain in 1985 and caused a similar problem with native vegetation. A culling occurred once the population on this island reached 450 individuals, but the killings caused the numbers to decrease to only 25 individuals.
Reintroduction efforts have been successful in recent years. In 2003, Monarto Zoo temporarily held eighty-five tammar wallabies from New Zealand. Out of these individuals, four have been released onto Innes National Park on Yorke Peninsula, where a population between one hundred and one hundred and twenty individuals now resides. Other areas where this species has been reintroduced include Avon Valley National Park and Nambung National Park. This species has suffered a significant amount of habitat loss and habitat fragmentation, which has caused inbreeding and other genetic issues in some populations. However, the tammar wallaby appears on the IUCN Red List with a conservation status of “Least Concern.”
Image Caption: Macropus eugenii (Kangaroo species). Credit: MattWake/Wikipedia (CC BY-SA 2.0)