Tasmanian Devil Page 5
The thick, largely non-prehensile tails of both species store fat. The devil’s tail is important in physiology, locomotion and social behaviour. During high-speed motion it acts as a counterbalance.
The jaw gape of both species is wide, at 75–80 degrees, although for different reasons: thylacines used their gape to seize and suffocate or crush prey, while the gape and powerful teeth of the devil enable it to tear and gulp large lumps of food in a competitive manner, as well as to crush bones in order to consume them.
The animals’ differences are pronounced. The devil’s blackness is a sure asset for a small nocturnal creature; the thylacine’s fawn or tan colouring shows a functional similarity to placental hunters such as wolves and wild dogs which hunt by day. An adult thylacine is about twice the weight and size of a devil. Anatomically it is considerably more streamlined than the squat, stout devil. This is because it is a cursorial predator, selecting its prey—generally a wallaby—and pursuing it relentlessly. Many early accounts refer to the thylacine’s unhurried, dogged pursuit of prey, wearing its victim down through exhaustion, though it was undoubtedly capable of sharp speed over a short distance.
There was a long-held view that the thylacine was fussy and selective, consuming only the heart, kidneys and vascular tissue of its freshly killed prey, while the devil was a rapacious carrion eater. Clive Lord, director of the Tasmanian Museum in the 1920s, wrote:
One or more Tasmanian devils will often follow a thylacine on its hunting excursions. The thylacine will kill a wallaby or other small animal, select a few choice morsels, and pass on. The devils will carry on the feast and consume the remnants, bones and all.5
Statements like this unwittingly consigned the two species to a strictly hierarchical relationship, and it is only in recent decades, through scientific studies, that the devil’s predatory abilities have been recognised—and the likelihood that tigers and devils coexisted in a robust relationship.
Is the devil unique or can it be likened to non-marsupial mammals? Convergent evolution results when unrelated species in unrelated environments evolve similar adaptations because they occupy similar niches. Understanding and appreciation of the Tasmanian devil will be enhanced by finding convergent ‘relatives’ elsewhere. There are three good examples: the northern hemisphere wolverine (Gulo gulo), the southern hemisphere ratel (Mellivora capensis) and the hyaenas (striped, Hyaena hyaena; brown, H. brunnea; spotted, Crocuta crocuta).
Wolverines are sometimes referred to as the devil of the north. Their powerful teeth and jaws are adapted for chewing frozen carrion and crunching bone. (Courtesy Daniel J. Cox, Natural Exposures Inc.)
Wolverines and ratels belong to the Mustelidae, the weasel family, which includes weasels, minks, polecats, otters, badgers and skunks.
Historically the wolverine has a broad circumpolar range, taking in Russia, the Scandinavian countries and North America. Despite the size of its range, in the words of the Wolverine Foundation, the umbrella organisation devoted to researching and protecting it, ‘Even today, the wolverine remains largely a mystery . . . one of the least understood and most fascinating creatures on earth’.6
Comparative skull drawings of a Tasmanian devil (top) and a wolverine (bottom), showing the similarities of a robust carnivore skull. (Ian Faulkner)
In the United States, wolverines were once found as far south as California but appear to be confined now to Idaho and Montana, although there have been recent sightings in the Rocky Mountains states. Their Canadian range is also shrinking. The wolverine occupies a predator–scavenger niche one level down from the top predators, which in its range include wolves, bears, mountain lions and lynxes. This is not dissimilar to the Tasmanian devil–thylacine relationship.
Devils and wolverines have heavy builds, short powerful limbs, small round ears, weak eyesight, an excellent sense of smell and large heads to support their powerful jaws. (A wolverine skull in David Pemberton’s office in the Tasmanian Museum and Art Gallery is often mistaken for a devil skull.) Both animals have white neck and throat patches, and are occasional tree climbers—only juveniles in the case of devils, while generally wolverines are ‘not considered to display arboreal behaviour’.7
Devils and wolverines are habitually described as nocturnal animals, but both species can be active during daylight. They are both regularly described as bear-like, due particularly to the shape of the head, the small eyes and round ears, broad chest when upright, glossy coat and pronounced claws. One of the Wolverine Foundation’s Frequently Asked Questions is whether the Tasmanian devil is a biological relative of the wolverine. (‘No . . . They may resemble each other physically, however they are distinctly different.’)8
Adult wolverines typically weigh 2–3 kilograms more than adult devils, much of which is fat for insulation, while their fur is long and thick and their pads broad for travelling in snow. Wolverines have low density distribution; devil densities vary from low to very high. Wolverines have an inbuilt fearlessness and will not hesitate to attack if threatened, whereas devils generally are timid. Wolverines use strong scents to mark their territory, which devils do not conspicuously do, being non-territorial (although devil latrines may serve a similar function). Wolverines, as solitary animals, are quiet, as are solitary devils, though both have a range of social vocalisations.
Like the devil, the wolverine’s food habits ‘are weighted to scavenging’.9 Wolverines are unfussy, opportunistic eaters and will cover large amounts of territory in search of food. They are known to attack incapacitated animals much larger than themselves but are generally recognised as voracious scavengers, so much so that early North American settlers nicknamed them Gluttons. Eggs, insects, birds, rodents, squirrels and hares all form part of their diet.
Convergent evolution is strongly evident in the reason for both devils and wolverines having very powerful jaws: the wolverine is a specialist bone-crusher, capable of crunching through an elk or moose femur for the valuable marrow. It also chews frozen meat.
Both have been hunted for their persistent, opportunistic preying on animals trapped for their fur—wallabies and possums in Tasmania, mink and marten in the northern hemisphere. And just as the devil had a bounty placed on it for supposedly killing lambs in Tasmania’s early days of white settlement, wolverines continue to be bounty-hunted across Scandinavia for their predation upon domestic reindeer and sheep.
Again, not unlike the devil, the wolverine is often regarded as a nuisance or worse, not least for its powerful, rank chemical secretions. In Native American folklore the wolverine is an ambivalent hero-trickster and a link to the spirit world. Interestingly, in North America it is sometimes called the Indian devil, and a 2002 video produced by the Wolverine Foundation is entitled Wolverine: Devil of the North?
The ratel, despite its common name of honey badger, is no longer classed in the badger sub-family. True badgers tend to be omnivores; ratels are predator–scavengers with a much greater tendency to carnivory. Hence, ‘In 1902 it was transferred to the Mustelidae on the basis of skull morphology and teeth [and] in 1912 a kinship with the wolverine Gulo gulo was suggested.’10
Ratels occur throughout Africa—parts of the Sahara excepted—the Middle East and India. Not surprisingly, given that vast distribution, they are adapted to many forms of habitat, from dense wet rainforest to semi-arid desert and sub-alpine heights. Devils showed a similar widespread distribution across the Australian mainland, and they occupy all parts of Tasmania.
The ratel, like the devil, is both a predator and scavenger. They have very powerful jaws. (Courtesy Mike Myers, Wilderness Safaris)
The ratel’s lower body is black, the upper body light, although colouration varies according to habitat; they are paler in more arid regions. It is not inconceivable that mainland desert devils may have displayed some degree of colour adaptation.
Devils and ratels are thickset and low to the ground; ratels weigh slightly more than devils and have a proportionately longer body. The ratel has ‘a m
assive head with a thick skull’.11 The jaw is powerful, though unlike the devil’s this may not be just for hunting and eating but also for defence: although considered ‘shy and retiring’,12 it has a well-known propensity for aggression against animals much larger than itself.
The devil’s peculiar lope is one of its most distinctive features, matched, however, by that of the ratel, which has a ‘slow, rather bow-legged lumbering gait that sometimes increases to a clumsy gallop’.13 Yet both, the ratel especially, are capable of running at considerable speed.
Convergent evolution is particularly evident in the diets of these unrelated, small, tough, nocturnal nomads. Devils eat ‘everything’—from tadpoles to dead cows and horses—and one of the first surveys of ratels in the wild, undertaken in the late 1990s in the Kalahari Desert by zoologists Keith and Colleen Bigg, found likewise; ratels ‘proved to be great opportunists, eating a range of 61 different species . . . food as small as social and solitary bee larvae, geckoes, scorpions, rodents and snakes to larger prey including springhares . . . birds and the juveniles of jackals . . . wildcat . . . fox’.14
Devils are closest of all to hyaenas, in particular the brown hyaena, which tends towards nocturnalism and solitariness, whereas spotted and striped hyaenas live in social clans of up to 80 with a rigid female-dominated hierarchy. Hyaenas and devils have a number of similarities: a shuffling lope resulting from a powerful forebody (hyaenas’ rear legs are actually shorter than the forelegs); an ability to consume up to a third of their body weight at one feed, whether carrion or fresh kill; like the devil, brown hyaenas regularly forage on beaches (their range takes in the Western Cape, Namibia and Angola); hyaenas use communal latrines for social purposes; the vocalisations of hyaenas— screams, giggles, whoops, growls and snarls—match or exceed the devil’s in range and complexity.
Hyaenas have a large sagittal crest on top of the skull for muscle attachment, giving the jaws great power—they are able to work their way through large bones. A frequently asked question is: Which species has the most powerful jaw: the hyaena, the wolverine or the Tasmanian devil? Some studies credit the Bengal tiger, the estuarine crocodile and the devil with the greatest jaw strength, though pound-for-pound rodents are probably way ahead—but they in turn must give way to ants!
Covergent evolution is evident in the range of similarities between the brown hyaena and the Tasmanian devil, including a tendency towards nocturnalism and solitariness.
(Courtesy Mike Myers, Wilderness Safaris)
Ignorance and superstition branded the hyaena a cowardly scavenger. Among its supposedly demonic attributes was an ability to change sex at will. The reality is that male and female hyaena genitalia are very similar, because females have a high testosterone count. Eric Guiler, intriguingly, claimed to have witnessed consecutive hermaphroditism—sex reversal—in a number of captured devils. David Pemberton and Nick Mooney, trapping devils at Granville Harbour in 2004, observed a devil with a non-functional pouch and scrotum.
One of the hyaena’s practical functions, disposing of human corpses, may well have led many Africans to regard it with unease. There are still some remote tribes of Maasai and Karamajong, however, for whom this method of corpse disposal is delivery of the individual’s spirit to the afterlife. It has an interesting echo of the wolverine’s link to the spirit world in Native American mythology. In pre-European Tasmania, might the devil have had such a relationship with the indigenous humans?
In a role not dissimilar to that historically attributed to devils—that they followed thylacines and ate the remains of their prey—hyaenas were incorrectly portrayed as bickering scavengers cleaning up after lion kills. Although scavenging is important, all three species of hyaena are active, highly successful pursuit predators. And like devils, they will opportunistically eat their own.
Despite the relationship between the Tasmanian devil and the thylacine, the devil is taxonomically closer to the other members of the Dasyuridae family, the quolls and the tiny mice-like marsupials—dibblers, antechinuses, kowaris, mulgaras, kalutas, phascogales, planigales, ningauis, dunnarts and kultarrs. (The more distantly related numbats, bandicoots, bilbies and the marsupial mole make up the rest of Australia’s sub-order of carnivorous marsupials.)
Quolls are well covered with spotted fur, have long tails, pointed facial features and sharp teeth. Two of the four species are found in Tasmania, the abundant eastern quoll (Dasyurus vivevrinus, once called the native cat) and the larger, less common spotted-tailed quoll (D. maculatus, tiger cat), which weighs up to 7 kilograms. Both species were once common across the mainland, but the eastern quoll is extinct there now and its larger cousin reduced to rump populations. Quolls are excellent hunters and prey on many invertebrates, reptiles, rodents, possums and small macropods. They climb very well, and birds and sugar gliders are included in their prey. But carrion also forms an important part of the diet, while rubbish-dump scavenging, poultry raiding, corbey grubs and fruit all add to an impressively varied diet.
The great mammalogist John Eisenberg visited Tasmania in 1990 on sabbatical. He had recently published The Mammalian Radiations, the most comprehensive summary of mammal evolution to date. Earlier in his career he had published studies of the behaviour of Tasmanian devils, and while in Tasmania he discussed with zoologists the concept of the carnivore guild and its functioning as a unit. His seminal thoughts and discussions contributed to the work and management directions which followed.
In his book (subtitled An Analysis of Trends in Evolution, Adaptation and Behaviour) Eisenberg first conceptualised the importance of studying a marsupial carnivore guild rather than individuals in isolation.15 Menna Jones’ resulting guild-structure findings derive from dentition studies carried out in the field and on skulls held in Australian collections. She showed that the relationship between devils and quolls evolved as one of direct competition. She sought to determine the role of such competition in structuring body size, habitat usage and diet. In general, species will space out in a habitat according to their own size and the size of their prey. It is called equal spacing.
A major finding was that, for this to be achieved, ‘the spotted-tailed quoll had to redefine itself in an evolutionary sense’.16 And it happened quickly: Jones puts the evolutionary timescale of this at as little as 100 to 200 generations, a generation being two years. While devils and the small eastern quoll are sufficiently different in size as to have minimal dietary overlap, the larger spotted-tailed quoll is in the middle, and therefore in competition with both. Jones believes that this may explain why it is the rarest of the three. How did she arrive at these conclusions?
The spotted-tailed quoll competes with the devil for both live prey and carrion.Devils are frequently blamed for raiding poultry yards, when quolls are the more likely culprit. The spotted-tailed quoll, once commonly known as the tiger cat, is extinct across most of mainland Australia and no longer common in Tasmania.
(Courtesy Dave Watts)
Skulls and skeletal material held in collections across Australia were measured. Particular attention was paid to dentition, with arrays of data compiled to create an index of tooth strength, as opposed to mere changes in tooth size over time. As well, the size and therefore strength of the temporalis muscles, the jaw-closing muscles, were measured by dimensions taken off the skulls. Tooth strength and jaw strength determine the size of prey a particular species can take. Analysis of the data indicated ‘intense competition in Tasmania . . . anything other than equal spacing means two species are going to rub up against each other, hence enforced equal spacing. We got equal spacing in the jaw-closing muscle, tooth strength, and average prey size. That’s pretty neat.’17 Estimates are that the eastern quoll is three times as abundant and the (pre-disease) devil six times as abundant as the spotted-tailed quoll.
This photograph offers rare proof of the predatory ability of the spotted-tailed quoll.
This one has chased down and is killing a pademelon. (Courtesy Michael Good)
> As the Australian continent dried out and heated up, the paucity of grazing or browsing vegetation shrank not only the megafauna but their replacements as well. Yet in this respect the Tasmanian devil is a veritable giant. Quolls aside, an adult male devil is up to 150 times larger than its closest marsupial relatives. They’re also completely unalike, an indication of how varied the evolution of Australia’s marsupial carnivores has been.
Thus the swamp antechinus (Antechinus minimus, ‘smallest hedgehog equivalent’) distributed across Tasmania and coastal Victoria, weighs about 65 grams. A strictly nocturnal insect eater and ground dweller—unlike the even smaller brown antechinus (A. stuartii) which likes to live in trees—this tiny marsupial is described as the smallest of the quolls. A unique feature of the antechinuses is semalparousness, the death of the male after sex. (It is also a feature of the life cycles of squid and flying ants.)
A male dusky antechinus in its favourite habitat of forest leaf litter. The tiny antechinus, weighing just 65 grams, is closely related to the Tasmanian devil. Males die within three weeks of mating, a feature of young devils since the onset of DFTD.
(Courtesy W.E. Brown)
The little red antechinus (Antechinus rosamondae), which weighs about 40 grams and preys vigorously on lizards, seems to owe its precarious existence along the mid-north coast of Western Australia to the fire-resistant, inedible woolly spinifex in which it lives.
The kowari (Dasyuroides byrnei) of central Australia, one of a number of marsupial species that become torpid during cold weather, is also a fierce hunter and vocally aggressive: