Tasmanian Devil
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? Tasmanian
Devil |
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 A male Tasmanian
Devil.
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| Sarcophilus
laniarius ( Owen, 1838) |
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| Sarcophilius harrisii |
The Tasmanian Devil (Sarcophilus laniarius), also referred to simply as 'the devil', is a carnivorous marsupial now found only in the Australian island state of Tasmania. The size of a small dog, but stocky and muscular, the Tasmanian Devil is the largest carnivorous marsupial in the world. It is characterised by its black fur, offensive odour when stressed, extremely loud and disturbing screech, and viciousness when feeding. It is known to both hunt prey and scavenge carrion and although it is usually solitary, it sometimes eats with other devils.
The Tasmanian Devil became extinct on the Australian mainland about 400 years before European settlement in 1788. Seen as a threat to livestock in Tasmania, devils were hunted until 1941, when they were officially protected. Since the late 1990s devil facial tumour disease has reduced the devil population significantly and now threatens the survival of the species, which may soon be listed as endangered. Programs are currently being undertaken by the Tasmanian government to reduce the impact of the disease.
Taxonomy
Naturalist George Harris wrote the first published description of the Tasmanian Devil in 1807, naming it Didelphis ursina. In 1838 the devil was renamed Dasyurus laniarius by Richard Owen, before being moved to the genus Sarcophilus in 1841 and named Sarcophilus harrisii, or "Harris's meat-lover", by Pierre Boitard. The latest revision of the devil's taxonomy, published in 1987, has changed the species name to Sarcophilus laniarius, although the name S. harrisii is still widely used. The Tasmanian Devil is the only member of the genus Sarcophilus. Phylogenetic analysis shows that the devil is most closely related to quolls, and more distantly to the extinct Thylacine (Tasmanian Tiger).
Physical description
The Tasmanian Devil is the largest surviving carnivorous marsupial in Australia. It has a squat and thick build, with a large head and a short, stubby tail. The devil stores body fat in its tail and an unhealthy devil often has a thin tail. Unusually for a marsupial, its forelegs are slightly longer than its hind legs. Devils can run in bursts at the impressive speed of 13 kilometres per hour (8.1 miles per hour). The fur is usually black, although irregular white patches on the chest and rump are common. Males are usually larger than females, having an average head and body length of 652 mm, with a 258 mm tail, and an average weight of 8 kg. Females have an average head and body length of 570 mm, with a 244 mm tail, and an average weight of 6 kg. The average life expectancy of a Tasmanian Devil in the wild is estimated at six years, although it may live longer in captivity.
The devil has long whiskers on its face and in clumps on the top of the head. These help the devil locate prey when foraging in the dark, and aid in detecting the closeness of other devils during feeding. When agitated, the devil can produce a strong odour, its pungency rivalling even the skunk. Hearing is its dominant sense, and it also has an excellent sense of smell. Since devils hunt at night, their vision seems to be strongest in black and white. In these conditions they can detect moving objects readily, but have difficulty seeing stationary objects. An analysis of mammalian bite force, corrected for body size, shows that the devil has the strongest bite of any living mammal. The power of the jaw is in part due to its comparatively large head. A Tasmanian Devil also has one set of teeth that grows slowly throughout its life.
Reproduction
Females start to breed when they reach sexual maturity, typically in their second year. At this point, they become fertile once a year, producing multiple ova while in heat. Mating occurs in March, in sheltered locations during both day and night. Males fight over females in the breeding season, and female devils will mate with the dominant male. Devils are not monogamous, and females will mate with several males if not guarded after mating. Gestation lasts 31 days, and devils give birth to 20–30 young, each weighing approximately 0.18–0.24 grams. When the young are born, they move from the vagina to the pouch. Once inside the pouch, they each remain attached to a nipple for the next 100 days. The female Tasmanian Devil's pouch, like that of the wombat, opens to the rear, so it is physically difficult for the female to interact with young inside the pouch. Despite the large litter at birth, the female has only four nipples, so that no more than four young can survive birth. On average, more females survive than males. Those who do not procure a nipple are typically eaten by the mother.
Inside the pouch, the nourished young develop quickly. At 15 days the external parts of the ear are visible. Eyelids are apparent at 16 days, whiskers at 17 days, and the lips at 20 days. The young start to grow fur at 49 days and have a full coat by 90 days. Their eyes open shortly after their fur coat develops—between 87 and 93 days—and their mouths can relax their hold of the nipple at 100 days. They leave the pouch 105 days after birth, appearing as small copies of the parent and weighing approximately 200 grams. Unlike kangaroo joeys, young devils do not return to the pouch; instead, they remain in the den for another three months, first venturing outside the den between October and December before becoming independent in January. Female devils are occupied with raising their young for all but approximately six weeks of the year.
Ecology and behaviour
Tasmanian Devils are widespread and fairly common throughout Tasmania. Found in all habitats on the island, including the outskirts of urban areas, they particularly like dry sclerophyll forests and coastal woodlands. The Tasmanian Devil is a nocturnal and crepuscular hunter, spending the days in dense bush or in a hole. Young devils can climb trees, but this becomes more difficult as they grow larger. Devils can also swim. They are predominantly solitary animals and do not form packs. They occupy territories of 8–20 km², which can overlap considerably amongst different animals.
Tasmanian Devils can take prey up to the size of a small wallaby, but in practice they are opportunistic and eat carrion more often than they hunt live prey. Although the devil favours wombats, it will eat all small native mammals, domestic mammals (including sheep), birds, fish, insects, frogs and reptiles. Their diet is largely varied and depends on the food available. On average, they eat about 15% of their body weight each day; however, they can eat up to 40% of their body weight in 30 minutes if the opportunity arises. Tasmanian Devils eliminate all traces of a carcass, devouring the bones and fur in addition to the meat and internal organs. In this respect, the devil has earned the gratitude of Tasmanian farmers, as the speed at which they clean a carcass helps prevent the spread of insects that might otherwise harm livestock.
Eating is a social event for the Tasmanian Devil, and much of the noise attributed to the animal is a result of raucous communal eating, at which up to 12 individuals can gather and which can often be heard several kilometers away. A study of feeding devils identified 20 physical postures, including their characteristic vicious yawn, and 11 different vocal sounds that devils use to communicate as they feed. They usually establish dominance by sound and physical posturing, although fighting does occur. Adult males are the most aggressive, and scarring is common from fighting over food and mates.
Conservation status
For some time, Tasmania was the last refuge of large marsupial carnivores. All of the larger carnivorous marsupials became extinct in mainland Australia shortly after humans arrived. Only the smallest and most adaptable survived. Fossil evidence from western Victoria shows that Tasmanian Devils retained a place on the Australian mainland until around 600 years ago (about 400 years before European colonisation). Their extinction is attributed to predation by dingoes and hunting by indigenous Australians. In dingo-free Tasmania, carnivorous marsupials were still active when Europeans arrived. The extermination of the Thylacine after the arrival of the Europeans is well known, but the Tasmanian Devil was threatened as well.
The first Tasmanian settlers ate Tasmanian Devil, which they described as tasting like veal. As it was believed devils would hunt and kill livestock, a bounty scheme to remove the devil from rural properties was introduced as early as 1830. Over the next 100 years, trapping and poisoning brought them to the brink of extinction. After the death of the last Thylacine in 1936, the threat to the devils was recognized. The Tasmanian Devil was protected by law in 1941, and the population slowly recovered.
At least two major population declines, possibly due to a disease epidemic, have occurred in recorded history: in 1909 and 1950. The Tasmanian Devil's current population is thought to be in the range of 100,000 to 150,000, a density of approximately 20 devils per 10–20 km2 area. Tasmania and Australia prohibit the export of Tasmanian Devils and there are currently no animals outside Australia.
Devil facial tumour disease
First seen in 1999, devil facial tumour disease (DFTD) has ravaged Tasmania's wild devils, and estimates of the impact range from 20% to as much as a 50% decline in the devil population with over 65% of the State affected. Affected high-density populations suffer up to 100% mortality in 12–18 months. The disease has mainly been concentrated in the State’s eastern half, although in early 2005, three cases were confirmed in South Tasmania.
Wild Tasmanian Devil populations are being monitored to track the spread of the disease and to identify changes in disease prevalence. Field monitoring involves trapping devils within a defined area to check for the presence of the disease and determine the number of affected animals. The same area is visited repeatedly to characterise the spread of the disease over time. So far, it has been established that the short-term effects of the disease in an area can be severe. Long-term monitoring at replicated sites will be essential to assess whether these effects remain, or whether populations can recover. Field workers are also testing the effectiveness of disease suppression by trapping and removing diseased devils. It is hoped that the removal of diseased devils from wild populations should decrease disease prevalence and allow more devils to survive beyond their juvenile years and breed.
Two 'insurance' populations of disease-free devils are being established at an urban facility in the Hobart suburb of Taroona and on Maria Island off the east coast of Tasmania. Captive breeding in mainland zoos is also a possibility. In May 2005 a recommendation was made to include the devil on the Tasmanian Threatened Species list as a vulnerable species, which means that it is at risk of extinction in the "medium term".
The decline in devil numbers is also seen as an ecological problem, since its presence in the Tasmanian forest ecosystem is believed to have prevented the establishment of the Red Fox, illegally introduced to Tasmania in 2001. Foxes are a problematic invasive species in all other Australian States, and the establishment of foxes in Tasmania would hinder the recovery of the Tasmanian Devil.