by David Owen
A variety of sounds are produced, including an open-mouthed hissing and a loud, staccato chattering, both made in response to threats from predators or other kowaris . . . Vigorous tail-switching, reminiscent of an angry cat, is used as a threat display.18
The red-tailed phascogale (Phascogale calura) survives in Australia’s arid centre through an impressive adaptation: it is immune to the poisonous plants upon which it feeds, as are the native carnivores which prey upon it. But the poison fluoroacetate, found in the Australian legumes Gastrolobium spp. and Oxylobium spp., kills introduced species.
An unusual adaptation is that of the long-tailed planigale (Planigale ingrami), one of the world’s smallest mammals (the average male adult weighs 4.2 grams). Its head is flattened so that it can enter cracks and narrow spaces in search of the insects, lizards and small mammals which it attacks with ferocity.
A species as endangered as the spotted-tailed quoll, and matching the devil for size, now has full claim on being Tasmania’s top order predator. The wedge-tailed eagle is a supreme hunter, one of the world’s largest eagles. This majestic raptor, although distributed across Australia and New Guinea, is listed as vulnerable in Tasmania (subspecies Aquila audax fleayi). Its diet is a practical one, relying generally on possums, wallabies, rabbits, hares, birds and carrion. This means that wedge-tailed eagles and devils are direct competitors.
The eagle, like the thylacine, has long been demonised as a lamb-killer and has endured heavy persecution. Indeed, the formation in 1884 of the Buckland and Spring Bay Tiger and Eagle Extermination Society set in motion the Tasmanian parliamentary debates that were to signal the extermination thylacine. Well over a century later the ‘wedgie’ continues to be persecuted, with some rural Tasmanians taking a gun to it when they can.
The wedge-tailed eagle, one of the world’s largest birds of prey, is considered to be Tasmania’s top order predator now that the thylacine is extinct. Human alteration to the land, as well as direct persecution, have adversely affected both species for over two hundred years. The parent bird is on the right. (Courtesy W.E. Brown)
If the European red fox becomes established in Tasmania, as it is on mainland Australia as an introduced species, it will compete directly with the devil—for prey, for dens and as a predator of devil young. In combination with DFTD, the fox may unwittingly hasten the Tasmanian devil’s extinction. (Courtesy W.E. Brown)
Finally, there is the European red fox, long established on the mainland as an introduced species and potentially becoming established in Tasmania. Just as the devil may have inadvertently hastened the end of the thylacine, an ineradicable fox population may do the same to a heavily decreased devil population. But should this eventuate, the highly competitive, efficient fox should not be made the scapegoat for having been introduced to Tasmania.
4
‘MADE FOR TRAVELLING
ROUGH’: DEVIL ECOLOGY
Little Devil only wanted milk for several days given by a bottle while being cradled in my arms and loved being cuddled and would emit the most piercing sound when he had finished feeding. Little Devil lived in an old meat safe near the pot belly stove during the day in the kitchen and at night would come out for his meat and biscuits, but should anyone other than myself be in the kitchen he would retreat until all was quiet . . . Eventually the kitchen door was left ajar so he could come in and out at night, this happened for some time before he decided he was old enough to make it on his own. I guess like all teenagers he grew up. It will always remain one of my most treasured memories.
DONNA COLEMAN, GORDON
In its evolutionary journey the Tasmanian devil has travelled remarkably well. And quickly: known devil fossils date back no more than 70 000 years and over that time the animal has undergone little change to its body plan other than dwarfism. Its physical and behavioural characteristics helped ensure its success as one of the seven extant large-size marsupial carnivores of Australia and New Guinea.
The squat, muscular body and short strong legs enable it to lope long hours in search of food and, in the case of males, reproductive partners. Because they are large, the head and neck have increased functional significance in feeding. The devil’s profuse, wiry vibrissae (whiskers) grow in patches from the tip of the chin to the back of the jawline, and are long enough to extend beyond shoulder width, acting as sensors during night movement, feeding and communication.
Devils, like dogs, have 42 teeth. (Cats have just 30.) Devils keep their original teeth, which continue to grow very slowly throughout the lifetime of the animals—they are not replaced.
The long claws are designed to dig efficiently, for denning and in search of food, and to firmly grip prey to facilitate chewing and gnawing. The sense of smell is acute and can detect food up to a kilometre away.
This structural emphasis on feeding places the devil in the company of one of nature’s iconic loners, the great white shark. A big old male devil has a shark-like forward torso, resulting in a great neck and head with a full but definite taper, providing immense power, out of proportion to the overall body.
The reproductive cycle of the devil is highly synchronised, but not inflexible. Female devils ovulate up to three times during the three-week breeding season, usually in late March, and copulation is almost continuous for up to five days at a time. The male goes to great lengths to keep other males away from his mating partner, keeping her prisoner in the copulation den with little chance to eat or drink. One thirsty male was observed dragging a female with him from a den to a water source and back to the den.1 David Pemberton and the Mount William ranger Steve Cronin once monitored a male and female in an underground mating den in the wild. The animals hadn’t moved from it for eight days and nights, so, wondering if they had died, Pemberton dug a narrow hole through to the burrow and put his arm down, holding a small mirror. His colleague shone a torch onto the mirror, which revealed a threatening set of bared devil teeth.
However, the intensity of male competition generally ensures that during a normal breeding season males breed with more than one female. Menna Jones’ studies of breeding indicate that females can be selective, and this means that in combination with multiple sperm donors the female optimises her chances of delivering the best available genetic offspring.
At birth, Tasmanian devils are tiny, as shown by these four newborns on a coin.
(Courtesy Nick Mooney)
At birth a Tasmanian devil is no larger or heavier than a split pea. A prime four-year-old male is some 15 000 times heavier, at about 11 kilograms. (In comparison, from birth to maturity the average domestic cat increases in weight about 20-fold.) At six years the male will be dead, having sired perhaps sixteen offspring. An adult female, weighing about 7 kilograms, has on average four breeding seasons, producing about twelve offspring during her lifetime. The mating season is three weeks; pregnancy lasts just eighteen days; the young are dependent on their mother for at least nine months, which means the female then has little time to herself before the next mating season. This demanding cycle means devil populations can theoretically double in size each year, an excellent safeguard against high mortality in both juvenile and adult populations.
A female devil has four nipples in her marsupium and litters of three or four pups are common, which helps balance out the high juvenile mortality rate. David Pemberton found a healthy 80 per cent of two-year-olds carrying pouch young during his fieldwork study. The mother stands to give birth. Twenty or more tiny embryos leave the womb and travel up to the backward-opening pouch in a stream of mucus. The first arrivals clamp to the teats, which swell in their mouths, so that the newborns become firmly attached to their mother. This ensures they do not fall out of the pouch and is an important survival factor.
Devils are usually born in mid-April, that is, mid-autumn, ensuring they won’t be weaned and have to face the world alone until long after Tasmania’s challenging winter has passed. DFTD, however, has produced a dramatic shift in reproductive behaviour, with a sc
atter of births across the seasons rather than
Baby devils begin to grow fur when they are twelve weeks old. Their sturdy tail is as long as their torso and has important functions including balance, storage of fat and communication. (Courtesy Collection Tasmanian Museum and Art Gallery) exclusively in autumn, and a high number of males competing for perhaps just one receptive female.
In 1934 David Fleay managed to breed devils in captivity and wrote a fine, precise account of it:
In the first days of June four tiny, pink, naked and blind babies each a half inch in length had betaken themselves to their mother’s pouch. Shortly after this the father was removed to bachelor quarters, for the mother now showed resentment at his presence by whining growls which rose abruptly in pitch and volume whenever the male attempted to enter the rock shelter. Early in August at the age of seven weeks the thick-set babies in the pouch had grown to a length of two and three quarter inches. They were still pink and hairless but now it could be seen that their tiny limbs moved actively as they clung tenaciously to the teats within the pouch. They also made slight squeaking noises and with increasing bulk the hind quarters of one quadruplet projected from the pouch as the mother moved about.
Meanwhile she had become somewhat fastidious for a Devil, disdaining raw meat but delighting in rats, birds, eggs, frogs and rabbit heads. Towards the middle of August a great change came over the appearance of the youngsters as the ear tips and then other regions of the skin began to show dark pigment. The pouch too, developing with the family, was far more relaxed and roomy. At eleven weeks the dark pigment of the young had become sufficiently pronounced to throw into strong contrast the future white chest and rump markings. The quiet nervous mother accepted the frequent handling with no sign of resentment. Progress of the little Devils was now quite phenomenal and on October 1st at fifteen weeks of age they first released their till then continuous grip on the teats. They were well furred and their eyes had opened. From these observations it is obvious that the mother must carry her cumbersome family with her for at least fifteen weeks after their birth. But from this time on the youngsters may be left at home in the nest, allowing the mother the freedom necessary for successful ‘scrounging’.
When lifted away from the parent the youngsters uttered anxious yapping cries and on being released again clung quickly to the fur of her sides with teeth and fingers—the fore-paws having unusual grasping powers so that the young Devils are expert climbers. On being disturbed from sleep when sheltered by the mother’s body, the little fellows lost no time in gripping her extended teats, from which it was almost impossible to dislodge them until firm pressure with a fingertip over the nostrils caused their mouths to open. At the age of eighteen weeks the ‘play age’ was apparent . . . At twenty weeks they were seven and three quarter inches in body length with small tails adding a further three inches. They still clung tenaciously to the mother’s teats when drinking . . . It was five months before they ceased to rely on their mother’s milk for nourishment and unfortunately we lost two of them before they had abandoned the maternal apron strings. One squeezed through the chain netting of the enclosure and was never heard of again while the other sickened and died. The mother and remaining two youngsters showed the thorough scavenging traits of their kind by immediately devouring the whole carcass, except the head, of their deceased relative even though food was plentiful.2
Devils are weaned in summer, between December and February, after which they disperse widely, but with a higher proportion of females remaining in the natal areas. Up to 60 per cent die before reaching maturity, according to Guiler. Even so, the sudden increase in numbers over summer can give the appearance of a plague, because juveniles are more crepuscularly active than adults and at dusk are regularly seen on roads, scavenging in paddocks or on beaches and around farm complexes.
Newly weaned devils become solitary at once. They are agile foragers, taking a wide variety of small invertebrates and vertebrates, and their excellent climbing ability enables them to obtain food from trees, such as grubs, and eggs from birds’ nests. They are fully grown and mature by the age of two.
The uniqueness of a solitary animal surviving through communal feeding sets the devil apart from other carnivores. Young devils quickly learn to congregate at the site of a carcass, drawn by the scent and, just as importantly, the vocalisations of those that have already arrived at the site. Conflict over a carcass is avoided through a ritualised behaviour ensemble.
Young devils are agile foragers and good climbers. This picture was taken at Mrs Roberts’ Beaumaris Zoo in the early 1900s. (Courtesy Collection Tasmanian Museum and Art Gallery)
Young devils, because they are active at dusk, have the advantage of arriving at food sources before the more competitive adults. This, however, puts them into competition with spotted-tailed quolls, which are also active diurnal feeders.
Feeding devils communicate with each other through a range of visual postures, vocalisations and a suite of chemical signals. It was once assumed that dasyurids made little use of visual communications because they are nocturnal. Devils have night-adapted eyesight and their white chest and rump flashes are distinctly visible at night. Interaction between devils at feeding sites takes the form of a ritualised contest, with the dominant feeder not being displaced until it has gorged itself.
A devil eats up to 40 per cent of its body weight per meal every two to three days. Eating such a large quantity of food in a short space of time—about half an hour on average—often results in the animal waddling off with a distended belly and lying down not far from the feeding site; a devil in this state is easy to approach. It is likely that the absence of other large predators has facilitated this form of feeding, even during the long period when thylacines were Australia’s largest carnivore. This lends some support to the belief that thylacines ate only choice parts of their prey, leaving the rest to devils and other scavengers.
Being a scavenger able to digest a wide variety of food matter—flesh, fish, bone, invertebrates, fruit, vegetation—was an advantage to the devil’s survival. It may also be that the thylacine’s narrower food base (and less productive breeding cycle) meant that it existed in comparatively lower numbers, leaving it more vulnerable to changed circumstances (human predation) than the devil.
The number of devils feeding together is generally determined by the size of a carcass: groups of two to five are common. The first arrival is the dominant feeder (unlike communal hyaena feeding, where the higher ranking clan members feed before subordinates), which makes way for a challenger once it has gorged itself. The size of the carcass affects the extent to which the feeding devil will chase off a challenger: the feeder defends the amount of food it needs, not the entire carcass.
Satiation, rather than dominance, is the most likely information conveyed by the ritualised interactions. This means all devils, small and large, resident and transient, can feed together. It is an efficient way of sustaining a population.
David Pemberton was the first to make scientific field studies of devils feeding in the wild. The absence of unrestrained aggression while feeding, and the complex behaviour occurring in its place, was a critical discovery, overturning popular (and some professional) perceptions of the animal, as in this supposedly informed 1984 account of feeding devils by a popular natural history author: ‘They behave like a brawling mob, having, so far as anyone knows, virtually no social organisation or restraining instincts’.3
Pemberton recorded only one instance of physical injury in 119 interactions during feeding, with one animal chasing and biting another on the rump. On two occasions he also observed jaw-wrestling, where devils stood on their hind legs with forepaws on each other’s shoulders or chest and their jaws interlocked. The animals vocalised constantly while shaking their heads from side to side. Although there was no obvious physical damage to the animals, the nature of the interaction appeared as if it could have caused extensive damage to muzzles or jaws. On each occasion the defeated
animal ran off into the bush with its tail in the air and fur fully erect, with the winner pursuing it and biting its rump whenever it was close enough.4
Examination of 150 trapped animals showed that 6 per cent had suffered injuries consistent with fighting during feeding or breeding, showing enough damage to the flesh of the face to leave teeth visible. These, however, were aged males with lame hindquarters and extensive hair loss on rump and tail, suggesting a physical deterioration other than that caused by intra-specific aggression. A third showed some form of wound, such as puncture holes on the back and rump and shortened, hairless tails. It doesn’t automatically mean that all the wounds were obtained while feeding; in fact, most wounds occur during the breeding season.
Pemberton recorded eight vocalisations between initiators and recipients at carcasses: a ‘snort’ made by expelling air through nostrils and mouth; a short, deep, low-intensity ‘humf growl’, often repeated; a short, deep, high-energy ‘bark’, seldom repeated; a ‘clap’ made by snapping the jaws together; monotone, vibrato or crescendo ‘growl-whines’; a ‘screech’, associated with defeat; a ‘sneeze’ and a ‘yip’.5
Pemberton also identified some 20 postures that reinforce the elaborate nature of the feeding interactions. They include:
• Neck threat—one nips at the neck area of the other, without making contact. These nips are repeated and the recipient responds by shouldering the initiator or attacking it face on.
• Gape—animals open their jaws for a few seconds as inter– actions take place.
• Lying down—the initiator of the behaviour lies down on its belly with the fore and hind feet extended. These animals are in full view of the possessor of the carcass, but do not physically interact with it.