AUSTRALIAN BUSHFLY (musca vetustissima)
Flies are the curse of the Australian outback. They are part of its fabric and ubiquitous like air. Breath with your mouth open and you will breath flies. Bite into your sandwich and you'll eat flies.
Unjustly, Australia's 20million odd cattle and sheep have been blamed for this plague. Cattle leaves 12 daily pads of poo per head, and flies fly for it, feast in it, lay their eggs in it. The result is
2000 new flies per pad (1)
However, flies had colonised Australia before white man's cattle did. The effect of cattle was to make massive hords even more massive. The early explorers battled flies just as today's tourists do.
One of the explorers, Ernest Giles, remembers:
‘The flies at the camp to-day were, if possible, even more numerous than before. They infest the whole air; they seem to be circumambient; we can't help eating, drinking, and breathing flies; they go down our throats despite of our teeth, and we wear them all over our bodies; they creep up one's clothes and die, and others go after them to see what they died of. The instant I inhale a flie it acts as an emetic. And if Nature abhors a vacuum, she, or at least my nature, abhors these wretches more, for the moment I swallow a vacuum is instantly produced. Their bodies are full of poisonous matter, and they have a most disgusting flavour, though they taste sweet. They also cause great pains and discomfort to our eyes, which are always full of them. Probably, if the flies were not here, we might think we were overrun with ants; but the flies preponderate; the ants merely come as undertakers and scavengers; they eat up or take away all we smash, and being attracted by the smell of the dead victims, they crawl over everything after their prey'.
And after another day of fighting flies:
‘It was impossible to get a moment's peace or rest from the attacks of the flies; the pests kept eating into our eyes, which were already bad enough. This seemed to be the only object for which these wretches were invented and lived, and they also seemed to be quite ready and willing to die, rather than to desist a moment from their occupation. Everybody had an attack of the blight, as ophthalmia is called in Australia, which with the flies were enough to set any one deranged. Every little sore or wound on the hands or face was covered by them in swarms; they scorned to use their wings, they preferred walking to flying; one might kill them in millions, yet other, and hungrier millions would still come on, rejoicing in the death of their predecessors, as they now had not only men's eyes and wounds to eat, but could batten upon the bodies of their slaughtered friends also. Strange to say, we were not troubled here with ants; had we been, we should only have required a few spears stuck into us to complete our happiness' (2).
The memories of the explorer Charles Sturt were equally fond of flies:
‘...the flies swarmed in hundreds of thousands... we observed that many (Aborigines) had lost an eye by inflammation from the attacks of flies. I was really surprised that any of them could see, for most assuredly it is impossible to conceive anything more tormenting than those brutes are in every part of the interior.... I continually wore a veil, or I could not have attended to our movements, or performed my duties. .. The flies being in such myriads around us, so that we could do nothing. It is, indeed, impossible for me to describe the intolerable plague they were ...from early dawn to sunset...' (3).
The tormentors were the Australian bushflies, one of 85 000 species of the order Diptera. These are the "true flies" which possess only one pair of wings for flight. The second pair is reduced to little knobs which are used for balance (4).
As the name suggests, the bushflies love the outdoors. They never come inside. They become active when the sun rises and go to sleep when it sets. They never tire in between. But they become tolerable during winter. As the temperature decreases, flies fly less. Their body temperature drops with the external temperature. Cold renders them immobile. Below 12ºC (53.6ºF) they don't fly at all and die when it gets colder. When the thermometer climbs above 35ºC (95ºF) they look for shade. They are happiest and most active in the high twenties (mid eighties F) (1).
Compared to the very alert housefly, which is hard to catch because its reaction is almost immediate, the bushfly is much slower. Maybe, it sees security in numbers, and the single fly is quite easily caught. Flapping their wings about 200 times per second bushflies fly with a pronounced buzz, but never exceed a speed of 8km per hour (5 mile/h).
Females are the nuisance of the species. Males wouldn't bother you - they simply hang around the females. These are after your protein. They get it from your skin and your saliva, tears in your eyes, the mucus of a runny nose and, of course, blood. Any wounds, the smallest cuts are a feast for flies. And dung is a protein bonanza. A fly's sense of smell is extraordinary. A cow pad will draw flies while still being delivered. The females are desperate for protein. They need it to produce eggs. Five weeks without intake of protein renders the female infertile.
A generation lost.
Undisturbed in laboratory conditions bushflies have been observed to mate for one hour and 20 minutes. This fertilises two batches of eggs, each containing 5 to 50 eggs - depending on the fly's size. The eggs are laid in faeces, a fresh cow pad is ideal. Smelling and tasting with her feet, the female will walk all over it. Laying takes its time, about one egg per minute. The eggs are laid in clusters. They are quite visible within the one millimetre range.
At hot weather of 39ºC (102.2ºF) it takes only 5 hours for maggots, or larvae, to hatch. But at 21ºC it takes 17 hours (69.8ºF). The maggots are blind, they grow by eating dung, and they are very sensitive to temperatures. A cold spell dropping below 12ºC will kill all maggots (53.6ºF), while 80% survive at 21ºC (69.8ºF). Too much moisture, like a few showers, or fast drying of the dung also affects survival rates.
Once grown up the maggots stop eating and leave the dung/cow pad - mysteriously always between midnight and dawn. Then they bury themselves in the soil and grow a puparium, which is an armour-like hardening of their skin. Inside this housing they metamorphose. The duration of this process, once again, is dictated by temperature and takes 3 days at 39ºC or 18 days at 18º (102.2º/64.4ºF).
They break free of the puparium as fully grown flies, though somewhat crumpled and colourless. Pigmentation happens later. To smoothen out body and wings the new flies take some deep breaths of air (4). They pump themselves up. Thus fully formed they cannot grow any more. They are trapped in an unchanging type of external skeleton. Large flies are large simply because they were able to eat lots of protein at maggot stage, while little flies were deprived of it as maggots. The little ones never seem to forget this and keep a frentic hunger for protein. That's why little flies pester you more than big ones.
Three days after their metamorphosis, if the temperature is right, flies can mate.
In very hot weather, they live just one week. At moderate temperature they can live up to four weeks.
They are very dependent on water, preferably the sweat of tourists. Without water a bushfly will not survive a single day (all 1).
Sources:
1) Most information taken from the book ‘The Fly in your Eye' by Jim Heath
www.viacorp.com/flybook/fulltext.html#bushflies
2) Ernest Giles: ‘Australia Twice Traversed - The Romance of Exploration'
3) Charles Sturt: ‘Expedition into Central Australia'
4) Encyclopaedia Britannica
AUSTRALIAN BUSTARD (Ardeotis australis) belongs to the order of the Gruiforms to which also the cranes belong and brolgas.
It is a ground-dweller, though it can fly with wings stretching out to almost two metres (6.5 feet). But it flies only when forced to. Consequently, it is loved by cats and foxes. Also called Bush Turkey, the bird was hunted extensively as a good meal. Today, the bustard enjoys a conservation status C - meaning near threatened. Laying only one to three eggs per season (usually only one), and their level of genetic exchange rather low, their population is decreasing. Some vague estimates believe that there are still 100 000 birds around, 99% of them in Australia. But they are not easily counted, because they scatter and, though not nomadic, they walk long distances for their food and water. Their diet is omnivorous: seeds and fruit, frogs, insects, little mammals and reptiles small enough to be swallowed whole.
The female lays her eggs on bare ground and incubates them for 24 days. The chicks watch mother for four days, then are able to find their own food.
They like open grass plains and low shrub habitats of north and central Australia
It is an attractive bird with a long white neck and a black cap on its head. Its wings are orangy brown. It reaches a turkey's height while its body reminds of a big duck.
The bird has three forward toes and no hindtoe, just like the emu. Its toes are comparatively short, which makes running on hard surfaces easier. And it walks in a strange halting fashion, stopping frequently to look around, circumspect and nosy at the same time.
Sources:
www.amonline.net.au/wild_kids/birds/bustard.htm
www.deh.gov.au/biodiversity/threatened/action/birds2000/pubs/australia_bustard.pdf
Brine Shrimp (Artemia salina)
Belongs to the order Anostraca, which are ancient crustaceans without a hard shell. Lake Eyre's brine shrimp belongs to 9 Anostracan species endemic to Australia. They are in the class of the Branchiopodae (gill footers) because they have their gills where the legs grow out of the trunk (1).
Brine Shrimps can live anywhere between Greenland and Australia, as long as the water is hypersaline. They can tolerate salinity of 35%. That is 13 times saltier than the average ocean's 2.7%. Even the very salty Dead Sea contains only 25% salt. But the shrimp has to keep its internal salt concentration lower than that of its surroundings. In fact, it is equal to that of freshwater animals (2). To cope with all that salt the shrimp acts like a desalination plant. After an intake of water the salt is separated and expelled through the branchia (gills) (3). Physiologically, the Brine Shrimp could live in sea water. It doesn't, maybe because that's a world heavily populated by competitors and predators. In the thick brine of Lake Eyre life is safer (2).
But when the water evaporates and salinity increases, oxygen becomes less and less soluble and the shrimps die leaving their eggs behind. These are really ‘cysts' containing the embryo whose metabolism has been set on hold (4). This ‘diapause' is reminiscent of the embryo-in-waiting of the kangaroo (where it is held inside the female body). The cysts can survive many years. During experiments they have been dried, frozen to minus 190ºC (-300ºF), heated to a boiling 100ºC (210ºF) and then placed in a saline solution.
They hatched. (2)
Once freshwater enters the lake again and dilutes the salinity the cyst hatches into a ‘nauplius', which is the first larval stage. Nauplii molt 15 times before they reach adulthood (4) which is a greenish 4 centimers (1.6in). They swim upside-down. For some reason they like their ventral surface - that is their tummy - to face the light. When being shone upon from below they promptly turn around again, towards the new light source (2). Swimming means rowing 11 pairs of paddle-like legs. A row of bristles at the back of their legs acts as filter. They catch tiny bits of organic particles which float by and push them towards the mouth.
The males use a pair of antennae to hold the female during mating.
As long as conditions are optimal the fertilised female will produce eggs which have fully developed inside her brood pouch and hatch into nauplius larvae as soon as they exit. It is called ‘ovoviparous' reproduction. But when conditions deteriorate, reproduction changes into ‘oviparous' mode. Now the female lays long-term eggs: those egg-like cysts. They have a hard casing. It's a tough package around dormant life designed to survive tough conditions: desiccation, heat and cold and wind-born travels. Then they wait to cheat bad times. Metabolic functions are shut down. Not really alive, yet also not dead, they enter the in-between state of ‘potential life'. They are the faunal equivalent to the floral drought avoiders, those ephemerals of arid zones which spend more time as seeds than being plants.
They play Sleeping Beauty. She needed a prince's kiss to wake up again. It's salty water for the brine shrimp.
For the remarkably diversified reproduction of shrimps see: 'Shield Shrimp' (further down)
Sources:
1) www.sience.lander.edu/rsfox/artemia/html
(sorry - content to this link not accessible any more)
2) ‘The International Wildlife Encyclopedia' (Dr.Maurice Burton / Robert Burton)
3) http://brineshrimpusa.com/greatsaltlake.phtml#8
4) http://ut.water.usgs.gov/shrimp/index.html
Knowles (Peter): "Australia's Wild Heart"
http://www.environment.sa.gov.au/parks/sanpr/lakeeyre/index.html
CAMEL (Camelus dromedarius- Arabian Camel )
Camels are ruminants which originated 40 million years ago in North America, from where they spread and vanished. One migration went south, the other northwest via the Bering Straits into Asia. Fossils indicate the existence of many species - some small like rabbits. The only survivors are the South American llama and alpaca, and the Asiatic camel, the two-humped Camelus bactrianus of the cold deserts of Central Asia. Until 6 000 years ago, these were the only remaining members of the camel family. The one-humped Arabian camel Camelus dromedarius is a domesticated breed from its Asian forebears. When this domestication came about is uncertain. But when the Queen of Sheeba visited King Solomon in 955BC her luggage was most probably carried by one-humped beasts (1).
Dromedarius, also called Arabian camel, grows to a height of 2m (just over 6 feet) at the shoulder, and to a length of 3m (10ft) from head down the neck and along the body. The tail adds another 45cm (1.5ft). The animal can weigh up to 410kg (1100lb) (1).
Only Arabian camels were introduced to Australia, the first in 1840 from the Canary Islands. They proved to be ideal for heavy work in arid zones, as draft animals, as beast of burden and for transport. For many of the early explorers camels were an indispensable means for opening up the continent. Camels were the 4x4 of the time. By around 1900, more than 10 000 camels had been imported (2).
The camel easily adapts to desert climate thanks to ist unique ability to vary its body temperature by up to 6ºC (about 10ºF) - a range that would kill most other mammals. While a human's temperature remains constant just under 39ºC/100ºF, the camel is much more comfortable and efficient with a lower temperature early in the day at around 34ºC (93ºF). While the day heats up, so does the camel's body temperature. At midday it might reach 40ºC (104ºF). This helps to conserve water. Though camels do sweat, they sweat less than other mammals. In addition, their thick coat insulates against heat and the cold desert nights (1).
Camels have broad soft feet with two large toes connected by a web. They are well adapted to walk on sand. And they can close their nostrils and have two dense rows of eye lashes to prevent sand from intrusion. There are hairs around their ears for the same protection.
The legs on each side move simultaneously. It gives camels their striding gait (1+3).
For loading, camels kneel down and rest on horny pads grown around their knees and chest.A camel loaded with 250kg (700 lb) can travel about 100km/day (60 miles), even in the heat of summer.
The big camel teams which supplied the centre, which worked on the Overland Telegraph line and carried bales of wool to the railheads used to travel about 25 miles/day (40km). They would load a sturdy bull with 600kg while 300-400kg were the norm for average camels. They could manage three days without a drink (2).
Their eating habits are not choosy. They get by on thorny plants, dry grass and the coarsest vegetation other animals would refuse, though they prefer lusher stuff when available (3).
Camels were the perfect carriers on the dry Nullarbor plain. Stories tell that camels went for 16 days without water - and that in 38ºC heat (100ºF). It sounds exaggerated but might have been made possible by the succulence of the chenopods. This also would explain the story of a camel after such a dry period drinking 200 litres (53 gallons) in one go, because of all the salt it had eaten with those succulent saltbush leaves. But to drink 115litres (25 gallons) after 3 dry days is common (4).
Contrairy to popular belief, the camel does not store water in its hump.
In the absence of water the camel draws on fluid from its tissue. It can do so for up to a quarter of its body weight and still function normally - though looking haggard and somewhat shrunk. By contrast, a human will experience extreme stress after having lost just 12% of body fluid. Man would draw that fluid from both, his tissue and his blood. His heart would then labour to pump this thickened blood. But in the camel's case the blood remains unaffected and so is the camel's performance. During a marathon drinking session all the lost fluid is immediately re-absorbed by the tissue (1).
The camel's hump holds a reservoir of fat for rough times. Oxidising this fat will also produce water. A one hundred pound hump of fat could thus be transformed into an additional reserve of 50 litres (13 gallons) of water - so goes the theory and a popular myth. However, the extra oxygen needed for such conversion would necessitate a lot of heavy breathing with much more moisture lost as vapour than gained from this operation (1).
The hump is really just a store of energy - an animal's backpack crammed with provisions for a long hike.
Camels produce normally only one calf after a long gestation period of up to 440 days. The animal becomes fully independent after four years, and sexually mature after five (1).
The early explorers, being European, used horses as beasts of burden and for transport. It took a while before the advantages of the camel in a hot and arid country gained recognition.
Ernest Giles had tried both on his attempts to cross the continent to the west and back again:
"The beautiful horse sinks into the insignificance of a pigmy when compared to his majestic rival, the mighty ship of the desert, and assuredly had it not been for these creatures and their marvelous powers, I never could have performed the three last journeys. ...nor should I now be alive. ... The country we had traversed was a most frightful desert, yet day after day our noble camels kept moving slowly but surely on, with undiminished powers".
Even spinifex, so hated by horses, hardly worried camels. Giles again:
"...the spinifex wounded the horses' feet, and disfigured their coronets, it also used to take a good deal of hair off some of the horses' legs; but in the case of the camels, although it did not seem to excoriate them, it took every hair off their legs up to three feet from the ground, and their limbs turned black, and were as bright and shiny as a newly polished boot. The camels' hair was much finer than that of the horses', but their skin was much thicker, and while the horses' legs were punctured and suppurating, the camels' were all as hard as steel and bright as bayonets."
However, they were animals very much with a mind of their own, and camelmanship was required to handle them: "...The old cow that he was riding would scarcely budge for him at all. If he beat her she would lie down, yell, squall, spit, and roll over on her saddle, and behave in such a manner that, neither of us knowing anything about camels, we thought she was going to die. ... the bull, Mustara, behaved much better. He was a most affectionate creature, and would kiss people all day long; but the Lord help any one who would try to kiss the old cow, for she would cover them all over with - well, we will call it spittle, but it is worse than that" (5).
Modern transport made camels increasingly redundant. ‘Camel trains' survived only in remote areas inaccessible to the car into the 1950s. But already by the mid 1920s most of the camels which had helped to build a nation, had been released into the wild. They established herds which, by the year 2000, had grown to an estimated population of 500 000 (2).
Ironically, having been purposefully bred in Australia, camels were exported back to the Middle East as superior specimen. A fledging industry for camel meat and hides has been established in Australia.
Governments introduced culling programs, but of all introduced animals classified as pest in Australia, the camel is the best integrated into the country's ecology.
Though there might be over 10 000 of them in the Simpson Desert alone, the camel's broad and soft feet don't compress and damage the ground as the hooves of other introduced species do, like cattle, sheep, horses, donkeys and pigs. Its main sin is to be a grazer which competes with natives for scarce resources during a drought.The camel can be regarded as a border case between pest and accepted immigrant. Perhaps, one day it will attain the same status as the Dingo (see 'Dingo' one further down), also an introduced animal, but now popularly accepted as part of the Australian fauna.
See also Nullarbor and Simpson Desert.
Sources:
1) The International Wildlife Encyclopedia (Dr.Maurice Burton / Robert Burton)
2) www.camelaust.com.au
3) Encyclopaedia Britannica
4) www.ksharpe.com/Word/AR36_C02.htm
5) Ernest Giles ‘Australia Twice Traversed - the Romance of Exploration'
Peter Knowles "The Whirlwind Country"
TIME/LIFE Books "Arid Lands" / Jake Page
DINGO (Canis lupus familiaris dingo)
Most Australians would regard the dingo, the wild dog, as being part of the establishment of their native fauna. However, the dingo is an introduced species. And it was not brought to Australia by Aborigines, as widely believed, but by Asian seafarers around 3 500 to 4 000 years ago. Dingoes were included on their boats as food - still a prized delicacy in some Asian societies.
Today's wild dingo in Australia still shares closer traits with the remaining original dingo population in Thailand than with dogs or hybrids.
The dingo is a domesticated line which diverged from the Arabian wolf Canis lupus arabs and the Indian wolf Canis lupus pallipes probably simultaneously at different locations. This divergence was triggered by a change of human lifestyle from hunter-gatherer to sedentary agricultural. It was a gradual change which occurred between 10 000 and 6 000 years ago.
The dingo is one early offshoot of a domestication process that lead from wolf to today's 600 odd breeds of dogs.
The oldest dingo fossil found in Australia is 3 450 years old. After their arrival in Australia dingoes adapted quickly to a wide variety of habitats: from the tropics to the hot arid plains of the centre and the cool mountainous southeast.
Aborigines formed a close relationship with the dingo. They used it as a hunting help and a companion and gave it its name. Watkin Tench, captain of the marines in the First Fleet, mentions in his ‘Narrative of the Expedition to Botany Bay' (1789): "...the only domestic animal they (the Aborigines) have is the dog, which in their language is called ‘Dingo'..."
The dingo was a totemic animal for the Aborigines.
The dingo is repected for its intelligence, its cunning and hunting skills alone or in packs. Though on average only 57cm (22in) tall at the shoulder, 1.2 metres (4 feet) from snout to tail tip and weighing
15 kilos, a dingo pack can successfully hunt grown red kangaroos (see further down) of 60 kilos and more by coordinating attack and trapping strategies.
The dingo is most active during dawn and dusk when hunting near watering places.
A dingo pack is organised into a social order of clear hierarchies with the dominant (alpha) male and female at the top and subordinate ranks of beta and gamma dogs beneath. Their breeding habits were dictated by the unpredictable boom and bust ecology that characterises much of the continent with certain droughts interrupted by seasons of plenty. Survival is of prime concern. Females come into oestrus once a year between April/May. They whelp a litter of between 2 and 10, usually 5 pups around June/August after a gestation of 60 odd days. Breeding times shift to about one month later in the cooler southern parts of the continent.
Regardless of season, whether food is plenty or scarce, only the litter of the dominant female is allowed to survive. While all subordinate females copulate, become pregnant and whelp, their pups will be destroyed/eaten by the alpha pair. This infantizide from the top doesn't bother the other females. While lactating, they all help with breast feeding the one litter allowed to remain, and all members of the pack will concentrate on its upbringing and to make it strong. Such alloparental behaviour ensures the fittest of the species to survive even through successive bad seasons. It ensures viable offsprings and that no resources are frittered away on those with lesser hope to live long enough to procreate. It resembles a form of natural Malthusianism.
The pups stop suckling at about 6 weeks. After 16 weeks they are fully independent, but usually remain in the pack. They are sexually mature within 2 years, and can reach an age of 10 years.
Pack-forming is common in the wild when isolated from human interference. Interference can disintegrate a pack.
Loners are not uncommon.
The dingo is held responsible for the demise of the thylacine, the Tasmanian Wolf or Tiger.
This marsupial carnivore about the size of the dingo was widespread all over the continent, but disappeared from the mainland about 3 000 years ago; that is about 500 years after the arrival of the dingo. The thylacine was a solitary animal with a stiff gate. The dingo was the swifter hunter. And the dingo's superior social organisation could cope better with lean times. Dingoes were the more clever competitors for few resources.
The Tasmanian Devil, another marsupial carnivore about half the size of a dingo, experienced the same fate. It was finally driven from the mainland 450 years ago, but survives in Tasmania, which dingoes never reached.
Another theory has it, that all three species could have survived in their specific niche were it not for disease and parasites introduced by the dingo.
The dingo has been hunted ruthlessly, poisoned, trapped and barred from pastoral lands by the longest fence ever made. The 5 400km (3 355 miles) dingo fence running from the Great Australian Bight north to the Bunya Mountains in Queensland was erected to protect the eastern sheep.
In the west dingoes were radio-collarded, then bait was laid. One campaign killed 90%, another 44% of collared animals. But despite such statistical successes, the dingo has survived. Europeans were the hunters, but also the suppliers of a cornucopia of rabbits - the dingo's main food source. Even prolonged droughts have been made less threatening. Once cattle begins to die because of lack of fodder, dingoes will thrive on its carrion. It is now recognised, that the dingo is not a prime cattle killer, but eats the carcasses of dead beasts.
A by-result of the ruthless killing of the dingo was an explosion of another introduced predator, the fox. Foxes might have hunted to extinction up to 65% of Australia's ground-dwelling mammals, among them the hare-wallaby and the lesser bilby. According to Chris Johnson of James Cook University in Townsville/Queensland, the dingo was the natural protector of Australia's small marsupials. *
What hunting and poisoning didn't achieve, man's best friend, the dog, might do. Australia's pure dingo population is shrinking rapidly, its gene pool being swamped by the mix with abandoned domestic dogs. Hybridisation is today's biggest threat to the dingo.
The colours of the pure dingo are ginger, black and a white (which is not an albino white). Characteristically, most have white underparts and white paws and tail tips. But in today's outback one might see a colourful palette of crossbreds. And one might hear sounds not heard from pure dingoes. They communicate over long distance with a rather mournful howl. It serves as a beacon to stray members of a pack. It also is a warning to potential intruders to stay out of a pack's territory. Close vocal communication is done by snuffs, moaning and a strange elongated bark-howl. Pure dingoes do not bark as dogs do.
Hybrids are more prolific breeders than pure dingoes are.
Sources:
Laurie Corbett "The Dingo in Australia and Asia"
http://www.canids.org/species/Canis_lupus_dingo.htm
*(New Scientist 11 Nov.06)
EMU (Dromaius novaehollandiae) is Australia's largest native bird and the world's second largest after the ostrich. It is also the second animal, together with the kangaroo, on Australia's coat of arms. It belongs to the ‘ratites', the flightless birds, to which also the Cassowaries belong. They are the emu's closest relatives in the family of the Dromaiidae.
Emus can reach 1.9m (6.2 feet) in height and weigh up to 45kg (100lb). The females are a little heavier than the males. In a good season the birds put on fat. This helps for a while through lean times. Even down to 20kg (44 lb) the emu functions quite normally. It is similar to the camel's ability to carry an internal larder to draw from when needed. In addition, when conditions get tough and energy expense has to be rationed, the emu can drop its body temperature by 4ºC. That slows down the bird's metabolism and sends it into a sort of torpor (1). (see also Simpson Desert)
The emu is omnivorous. Its diet consists of seeds and fruit, the young shoots of plants, insects and small animals. To assist digestion little gravelly stones are swallowed as well, and keys and bottle tops.
Distribution of the emu is Australia-wide on the mainland, including alpine areas. But the animal avoids the dense vegetation of rainforests. Open grasslands and woodlands are its preferred habitat. It used to be also in Tasmania where it is extinct now. Since it needs daily access to water the emu shuns extreme arid zones except after recent rain when fresh green is sprouting.
Like the Australian Bustard, emus are neither migratory nor settled in any particular place. They are nomads and their whereabouts are dictated by the availability of food and water. Emus seem to find it by following rain-bearing clouds. They might follow them for hundreds of kilometers, 15 to 25 kilometers per day (9-15 miles). The longest recorded movement of a tracked animal was 990km (615 miles) (2).
Emus look a bit cartoon-like with a long neck and long naked stick legs and a plump shaggy barrel for a body in between, around which the fluffy plumage and useless little wings wobble when the bird is in a hurry. And their run looks somehow theatrical with that little head on that long neck remaining primly poised on an even level no matter how bumpy the terrain (3). A drooping thick extension of the plumage might be called tail. The long neck comes handy only as a periscope when the grass is tall. In the preferred open grasslands there aren't many trees with fruit to stretch out to. Instead, mostly, that enormous length of neck has to bend all the way down to the ground to find something to pick. But the long legs are useful to clock 60km/h (40mph) for a short burst, and a single stride can cover easily two and a half meters (9ft) (4). And when that doesn't help to get away from a pursuer, the emu will stop running and start kicking. Those long legs are extremely powerful and efficient bone breakers. Surprisinly, despite their skinnyness, they are said to make the emu an excellent swimmer too. The feet have three foreward toes which can rip into the flesh of an attacker (the ostrich has two toes). The back toe is reduced to a little stump.
The plumage, which consists of soft hair-like strands, is a mat dusky grey-brown to dull black and looks forever dirty. The wings are reduced to 20cm stubs (7.9in) hidden under less feathers than there seem to be. They are double feathers: from the base of the main shaft grows an aftershaft producing a feather of equal length to the main one. And the feathers are soft and downy like those of little chicks - they are neotenous which means they have retained a juvenile feature (4). The wings hang loosely down, floppy and quite unlike the rigid structure of other birds' wings.
Emus' social behaviour isn't easy to categorise. They wander around solitary; or in little groups of half a dozen or less; or in flocks of hundreds.
During the southern summer (December/January), male and female become a close pair and stay together for about five months during courtship, mating, nest-building and egg laying. The female can lay up to 20 eggs, each 13cm (5in) long and weighing half a kilo (1.5lb). But a clutch of 7 to 10 eggs is more the norm. They are laid between April and June (5). Once that's done, the male turns quite aggressive and the female may simply wander off.
The male sits down for about 60 days and incubates the eggs. Incredibly, during this time the male is said not to eat, drink or defecate (5+6). His ability to gear his metabolism down makes this possible. However, not all emus know this rule, and males have been observed to leave the nest for some refreshments. But they do lose up to 8kg (17.5lb) during the incubation period.
The nest is a rough circle, around a metre across (3ft) of trampled grass, leaves and bark and usually next to a bush or tree.
Black-breasted buzzards have been observed to irritate the male so that he left the nest. The birds then dropped stones on the eggs to break them (4).
The chicks are covered in a creamy down with dark longitudinal stripes. They blend in well with the surrounding grass. Within 2 to 7 days they are able to feed themselves. At night they snuggle up under dad's soft plumage. Dad brings up the kids.
The chicks stay with the male for four months. After 6 months they are fully independent and will go their own way. But emu males in semi-arid regions have been observed to extend their parental care to 18 months. They will not start another breeding cycle until that duty is absolved. The chicks are fully grown after one year. After 20 months they are ready to breed.
Males and females look very much alike. The easiest way to tell them apart is by ear.
Females have an air sack attached to the trachea (windpipe) with which they produce a loud booming sound. Lacking this feature the male mumbles intimate little guttural notes (4).
The opening of the land and the establishment of many dams and flowing bores by farmers and graziers has advantaged the emu. Numbers have increased, there may be around 700 000 throughout Australia.
In the 1930s, farmers and government declared war on the emu because, as a grain eater, it trampled through fields. Even handgranades were used, but proved useless. The emu won. By now, emus have become true friends of farmers because they act like excellent insecticides. They are avid consumers of caterpillars. 3 000 of them were found in a single emu stomach (4).
In the old days emu oil was used for lighting and for some medicinal purposes. One emu could yield
15 litres (4 gallons) of oil (4).
Sources:
1) Mark Shephard "The Simpson Desert"
2) Atlas of Australian Birds
3) James Woodford "The Dog Fence - A Journey Across The Heart Of Australia"
4) The International Wildlife Encyclopedia (Dr.Maurice Burton / Robert Burton)
5) http://animaldiversity.ummz.umich.edu/site/accounts/information/Dromaius_novaehollandiae.html
6) http://www.amonline.net.au/birds/factsheets/emu.htm
Encyclopedia Britannica
Reader's Digest "Complete Book of Australian Birds"
KANGAROO
see: RED KANGAROO
MARSUPIAL MOLE (Notorcyctes typhlops): This shaggy animal grows tube-like to 18cm (7in), weighs between 40 and 60 grams and is so well covered under long silky fur, silver to pinkish and irridescent gold, that it would be difficult to distinguish front from rear were it not for the stubby tail. Loose sandy soils of Australian deserts with spinifex cover are its habitat. The triangular forefeet are made for digging, helped by a leathery snout pad; the hindfeet push the body forward into the ground, at a low angle, to a shallow depth of 10 - 20cm (4-8 in). But exceptions have been observed where the animal went 2.5m deep (8.2 feet) (1). It doesn't bother much about tunnels, as the mulgara does. As it inches foreward, the sand behind it fills in again.
On the surface the mole is an awkward shuffler, moving its forelimb simultaneously with the opposite rear limb (2). But once in the ground it ‘swims' deftly through the sand.
The animal's behaviour is erratic. It will ‘swim' subsurface for a metre or so, then come up - maybe for a breath of fresh air - and go down again for repeats. But, being extremely active one moment, it may fall comatose the next (3).
The mole seems to live on invertebrates, grubs and worms, ants, termites, all found underground. It has been seen catching a centipedes above, but then taking it away below for consumption (2).
The mole seems to be predominantly, but not exclusively, nocturnal. And it prefers the netherworld, where eyes are of no use. So they have developed backwards and are now just vestiges of former proper optical organs. There are no functional lenses any more, nor an optical nerve. Seeing has been replaced by, perhaps, just a sensitivity to light. And the ears might be doing the same. There are no pinnae (external ear shells) any more, though holes for an ear canal are still there (4). And the pouch opens to the rear, a logical adaptation for an underground forward-digger (5).
The Marsupial Mole looks like, and its behaviour is in many ways similar to, the totally unrelated golden moles of Africa, especially the Namib Desert Golden Mole Eremitalpa granti namibensis, which is a placental animal. The African moles are ‘true' moles, the Australian Marsupial Mole is not. It is an example of ‘convergent evolution' (6). Two unrelated organisms show the same preference for a certain habitat and then acquire the same characteristics to adapt to this habitat, though both evolved from quite different directions.
The moles mate in spring, and 4-6 weeks later the young are born, a litter of 2 - 5. The young fasten to teats in a well developed pouch. As all marsuspials, they go back onto the teat, intermittendly, until quite late into their growth (7).
Being a very elusive animal, it is not clear whether it is rare or rarely seen and simply hidden. Its status is ‘endangered' (6). Being blind, the mole is easy prey when on the surface for cats and foxes. And soil compaction by wandering stock and cars could be a threat to its habitat (5).
Notorcyctes typhlops has been found in the spinifex desert regions of the Northern Territory, Western Australia and in the north of South Australia. It is also called the Southern Marsupial Mole. There is a second very similar species Notoryctes caurinus, the Northern Marsupial Mole. Though there are no geographical borders between their habitats (6).
Sources:
1+2) http://theses.library.uwa.edu.au/adt-WU2004.0038/public/01front.pdf
3) Encyclopedia Britannica
4) www.ausemade.com.au/group/f/fauna/mole/mm.htm
5) www.deh.gov.au/biodiversity/threatened/information/factsheets/south-mole.html
6) http://en.wikipedia.org/wiki/Marsupial_mole
7) www.giveusahome.co.uk/australian/mole.htm
RABBIT (Oryctolagus cuniculus)
The first rabbits arrived in Australia with the First Fleet in 1788. All five of them disappeared from history - in contrast to the next shipment of thirteen. These were released, Christmas Day 1859, on a Victorian property near Geelong for the pleasure of the hunting class. As hobbies go, it was a most successful act. By the mid 1860s, 14 000 rabbits had been hunted already (1). It also became Australia's most expensive import which severely modified native fauna and flora.
In 1894, the first rabbits appeared at Eucla, the southern edge of the Nullarbor. At 1896, they were sighted at Charlotte Waters, central Australia (2). In 1947 a group of commercial trappers caught
20 000 rabbits per week in the Nullarbor. And there, at Rawlinna siding, 3 500 rabbits were estimated per square kilometre in 1975 (3). It has been estimated that the progeny of one breeding pair might number nine million within three years (3a).
Rabbits are Australia's worst animal pest.
Rabbits are voracious grazers. Being small and having opposed incisors they can nibble even the youngest shoots close to the ground,which are out of the reach of teeth of any other animal. And once the top of a plant is eaten, rabbits will dig up the roots. Preventing new growth and regeneration rabbits can lay a region bare of ground cover destroying both, the base of the food chain and the habitat of other animals. Thus, in central Australia, the rabbit may be responsible for the demise of the rat kangaroo (Bettongia leseuri), the bilby (Macrotis lagotis) and the hare Wallaby (Lagorchestes hirsutus) (4). In times of drought and as a last resort rabbits will eat bark. They will ring-bark trees and kill them (5).
Though introduced from England the rabbit is amazingly well adapted to survive in arid surroundings. This animal does not need to drink. A warren has been observed only 550m (1800ft) from a water source. Yet, none of the resident rabbits bothered to hop the distance for a drink. They didn't need to. Rabbits can obtain all their moisture needs from the plants they eat. And when vegetation gets scarce, rabbits concentrate urea and reduce water loss through urin by 80%. And they can dehydrate to a weight loss of 48% and still function. Thus, rabbits can survive a long time into a drought without being affected by it. This increases the devastating effect of droughts on other plants and animals (5).
The rabbit pest feeds the pest of cats and foxes as their favourite prey. When rabbits finally succumb to a drought and their population shrinks, then cats and foxes have to diversify to other small mammals and birds. Thus the rabbit has also been indirectly responsible for the devastation of native fauna.
With green pasture around rabbits can breed any time of the year continuously, and they do so. The gestation period is 28 day. Females (does) can become pregnant again within hours of giving birth. Depending on climate and conditions, rabbits can breed between 3 and 6 months of age (5). The litter size rarely exceeds 5 kittens.
During breeding times rabbits form hierarchical social groups with the dominant male and female at the top and more submissive members down along the ranks. They defend their territory which is clearly marked by pellets coated with anal gland secretions. And they rub objects with their chin glands, which exude a distinct smell. Intruders are fought or killed.
The reproductive output of rabbits is checked by a high mortality rate. It is quite normal that up to 70% of kittens die in their first month (5).
Myxomatosis decimated rabbit numbers in the 1950s. But growing resistance to it made this virus eventually ineffective. In the 1990s the calicivirus shifted the rabbit from pest number one to third position behind feral cats and foxes (1). It brought the rabbit population very successfully down in the dry hot centre of Australia. Here, native vegetation has sprouted again, and there is hope for animals which were on the danger list. However, in the wetter areas of southern and eastern Australia the result of the virus has been patchy.
Chemical warfare seems to be the only way to control this pest eventually. Natural disasters which can afflict the rabbit population, like a prolonged drought, offer only temporary respite from these voracious eaters. Due to its prolific breeding the rabbit always gains upper hand again even when starting from a low base. And for natural predators like foxes and dingoes the rabbit is no easy catch. When chased its swift zigzags are hard to match. And rabbits can reach a speed of 70 odd km/h (miles per hour).
Sources:
1) Sydney Morning Herald 28.5.04 (‘Rabbits back to public enemy No.3 as cats and foxes reign')
2) Laurie Corbett ‘The Dingo in Australia and Asia'
3) www.ksharpe.com/Word/AR36_C02.htm
3a) Peter Knowles ‘Australia's Wild Heart'
4) brochure by Parks Australia ‘Uluru - Kata Tjuta National Park'
5) Agnote ‘The European Rabbit - Pastoral Pest' http://kakadu.nt.gov.au/pls/portal30/docs/FOLDER/DBIRD_PI/ANIMALS/PUBLICATIONS/ANIMAL_MANAGEMENT/J42.PDF
RED KANGAROO (Macropus rufus) has become an Australian icon and, together with the emu, stands in the Australian coat of arms. Macropods (family Macropodidae) derive their name from Greek ‘Big Footers'.
It is the largest of the 62 living kangaroo species, a grazer in open forest and on the wide plains. The grasses of the sandy plains and leaves are its diet. Much preferred are fresh herbs and the soft grasses which grow in good years on the clay soils of the mulga. Then a male can make it to a strong and healthy 90 kilos. The average length of a red kangaroo is 1.5 meters followed by a tail of just over one metre (5ft + 42in).
The kangaroo's most obvious characteristic is its mode of locomotion. It is the only large mammal that hops at flying speed - the female is called the ‘blue flier'.
At low speed, it is a very inefficient way of moving. When just ‘walking' around while grazing the kangaroo moves awkwardly on all fives: the short forelimbs, the halfway folded rear limbs plus the tail. But for anything above 17km/h (10.5 mph) this animal is unbeatable in speed and grace and economy. It can attain a top speed of 55km/h (35mph). A constant run of about 20km/h (12mph) can be maintained for several hours without a sign of exhaustion. No other herbivore of similar size can match the kangaroo's speed without much greater energy expense. This efficiency is not so much due to strong leg muscles, but rather to a ‘unique ability to store elastic strain energy in their tendons' (2). In a low pre-jump position the tendons are strung like a tensed bow under the body's weight, and they release the stored energy into the jump. Thus a jump is a freeing motion that needs little effort, and a speeding kangaroo runs more or less on automatic. The release energy of the tendons can catapult a ‘roo 9m (29 ft) forward, or almost two meters high (6 ft) (3).
When speeding the tail acts as a necessary balancing device. It is powerfully muscelled and serves also as a stool when the animal bends it into an L-shape and sits on it.
The kangaroo's locomotion results also in a particular method of breathing which, once again, is an energy saver. While the hind legs stretch out for a jump they press air automatically out of the lungs. Moving forward to touch the ground they pump air back in (2).
These linked mechanics of moving and breathing minimise the effort for a maximal result. They were evolution's trick to defend against the dingo, the kangaroo's only natural predator. A study over 7 weeks observed a group of 5 dingoes kill 83 Red Kangaroos in the vicinity of a water hole.
The Red Kangaroo is an example of highly spcialised adaptation to the vagaries of desert life with its unpredictable swings between drought and bounty.
The natural drive towards survival of a species must emphasise the survival of the next generation. At first glance it seems paradoxical that young kangaroos need at least two years to develop from conception to sexual maturity. At such a very slow reproduction rate, a few bad seasons of prolonged drought could wipe out a species. But the kangaroo has beaten this predicament with an intriguing process.
When giving birth after 33 days of gestation, the female reclines on the ground and the young exists. It lands on mother's tail. The young - little joey - is the tiny size of an acorn and naked. It is also blind. It then starts an endless crawl through the dense forest of mother's fur up and up into the marsupial pouch. There joey attaches itself to a teat, so fast it would cause blood to tear it off.
In the meantime, the female falls pregnant again. However, while little joey grows in the pouch, a clever device kicks in, called embryonic diapause. It arrests the development of the new embryo at a ‘blastocyst' stage. Joey number two is kept on standby, as a safety deposit.
Number one opens its eyes after something like four months. Occasionally, it will leave the pouch for a few hops, look around, look at grass and nibble it. And the more grass it eats the less it will consume of mother's milk. This seems to be nature's signal to the waiting blastocyst to develop into an embryo. Once born, joey number two makes the same journey and fastens itself to teat number two. Joey number one divides its time by hopping around a little, then jumping back into the pouch and onto teat number one. And, like a pub serving different brands, the female now produces different milk for teat number two than for the teat of the first born. The first born will leave the pouch after about 8 months. It will be sexually mature in between two to three years. And while second joey keeps growing, a new blastocyst will be in waiting. The female kangaroo is continuously pregnant.
That's the routine in good times.
When times turn bad and resources get scarce during a drought, the female's diet will suffer and her milk will lack vital nourishments. Little joey's development on the teat in the pouch will wither. There will be less and less suckling, and within two months joey dies. But less suckling has initiated the growth of the blastocyst into an embryo and the birth of the next young. If the drought breaks and there will be fresh food and good milk, this young will make it. If not, it too will die within two months and the next joey will have a go. This cycle of birth and quick death will continue until it rains again.
Thus, joeysare produced virtually on the production line as canon fodder in the war between drought and the survival of the species. This mechanism ensures a quick rebound in numbers. A prolonged drought can cut a kangaroo population by more than 50%.
Occupation of the pouch leaves its traces. Periodically, as soon as they are mobile, the little ‘roos are evicted while mum does maintenance. Compared to body mass, she has one of the longest tongues of all animals. She uses it to wipe through the pouch and keep it clean (1).
The kangaroo itself derives little nutritive value fom the food it eats. It has to rely on little helpers to work on it first. They live by the millions in its stomach and are called protista, tiny micro-organisms in their own class not belonging to animals nor plants. They are specialised in breaking down the cellulose of the plant matter the kangaroo has eaten. By doing so they release the nutrients in the grass and pass it on to the kangaroo as their own waste product.
To accommodate these essential workers the middle section of the kangaroo's stomach has been stretched into a tube-like housing. One kangaroo species, the euro, has an unproportionately large stomach structure. It is one of the very few herbivores that graze on the tough spinifex. But its nutritional value is so poor that masses of that stuff have to be consumed to satisfy the body's needs. A single meal might consist of one eighth of the euro's body weight. And to break it down is hard work for the micro-organisms. So that meal stays in the stomach for a long time needing a large space.
The quite unrelated placental ruminants like cattle and sheep have adopted the same symbiosis between a host and its microbial tennants.
The kangaroo, an Australian native, is a comparative newcomer. The first fossil records, no more than a tooth or a bone, appear in the mid-Miocene around 15 million years ago. They point to animals rather the size of rats or possums. In the same stratum the fossil remains of crocodiles and flamingoes were found. At that time much of Australia was covered by rainforest, and that precursor of kangaroos lived in trees, like the marsupial koala does. It certainly did not hop.
That was learned only about 8myago, when the climate in the centre of the continent became drier. Rainforest changed into open grassland.
The kangaroo was one of the most successful genera to make the transition from tree climbing to hopping over open plains and eating grass. By 2myago they had grown to giant sizes. A beautifully preserved complete skeleton of Protocoptodon goliah was found in a Nullarbor cave. That kangaroo stood almost 3 meters (9 feet) tall. And it had a compatriot wombat the size of a car. The extinction of those giants began in the later part of the Pleistocene, around 30 000 years ago.
It coincided with the disappearance of large animals on other continents, like the American bison and the Eurasian mammoth. Whether the cause was a change in climate or human hunting techniques is being debated.
The latest change of environment was caused by the arrival of Europeans. Many species of kangaroos were decimated by loss of habitat or hunting; some disappeared. The great John Gould, in the 19th century, feared the same for the Reds: "I regret very much to say that the time may not be far distant when the opportunity to give a full-sized drawing of the head of this noble animal, taken from life, will not be possible".
He urged the ‘Anglo-Australians' "... to establish laws for the preservation of the large Kangaroos, the Emeu, and other conspicuous indigenous animals: without some protection, the remnant that is left will soon disappear..."
Though far-sighted for his time and correct in all too many instances, the Red Kangaroo and the Emu are still around. The conversion of large tracts of territory into grazing land supported by bores and dams has benefitted both. The Red is now seen in greater numbers than ever before.
Sources:
unless marked otherwise, information taken from:
Tim Flannery / Michael Archer "THE KANGAROO"
published by Kevin Weldon, 1985
1) Mary Smith, New Scientist 14.6.2003 ‘The Last Word'
2) www.fact-index.com/m/ma/macropod.html
3) www.thebigzoo.com/Animals/Red_Kangaroo.asp
SHIELD SHRIMP (Triops australiensis), also known as Tadpole Shrimp for its thin, forked tail. It belongs to the order of the Notostracae which carry their armour ('shield') on their back (Greek: ‘noton' = the back). As a crustacean it is a member of the class of the Branchiopodae (‘gill footers') since their gills are placed where their legs/feet branch off segments of the trunk. They have 11 pairs of legs. The genus ‘Triops' means ‘3 eyes' which consist of two compound ones and a third little naupliar eye top centre on its head. This third eye is retained from a larval stage and is only a rudimentary optical facility.
Shield Shrimps are ground dwellers and crawl under leaf litter for shade from the sun. They are omnivorous and feed on tiny bits of organic matter and the larvae of small aquatic ephemerals.
They are called ‘primitive' crustaceans because they are today almost the same as they were at least 150 million years ago -fitting perfectly into a niche environment.
Though related to the Brine Shrimp, Triops cannot cope with high salinity. It prefers freshwater or slightly brackish water in pools which must be temporary only. These occur, logically, mainly in hot/arid environments. But Shield Shrimps are not bound to this climatic zone. Their eggs are blown around the world and come to life quite happily everywhere except in arctic regions.
Depressions on top of Uluru harbour eggs of this shrimp. The climate is arid, the presence of water rare and only temporary. It's the shrimp's ideal habitat. Its eggs require drying out to be able to hatch again. Laying desiccated in the dust they can remain in diapause - dormant in a suspended state of metabolism - for many years (27 have been observed) (1). When rain finally comes the eggs hatch into pools without predators, without competitors. Life is short but easy.
After rain, those depressions on top of Uluru become for a while pools in which the shrimp eggs
re-hydrate. The first hatchlings are mostly females. And they start to produce the next generation with no need for mating. The female develops diploid eggs, that is eggs which contain the full number of chromosomes. A male's sperm cannot penetrate these eggs for fertilisation. This asexual reproduction is called diploid ‘parthenogenesis'(from Greek ‘parthenos' = virgin: virgin birth).
The eggs are produced ovoviparously (Latin:‘ovum'= egg / ‘parere'= to give birth): life develops fully in the eggs inside the female's brooding pouch and hatches a soon as the eggs exit her body. Diploid parthenogenesis is the quickest way to make babies before the water evaporates. It is a system in a hurry in a race against the sun.
Once conditions turn critical, when oxygen in the water becomes depleted or the water recedes, the females produce haploid eggs with half the number of chromosomes. These eggs need male sperm to be fertilised and to receive the second half of chromosomes. They are called ‘winter eggs' because they have a thick covering to protect the dormant embryo for a long wait. They are shrimps long term investment. They also add genetic diversity to a species.
The eggs will be blown about, end up on mountain tops or in the dust of the desert. Among wingless creatures, the Shield Shrimp must be the widest travelled animal.
Many Triops populations have predominatly females with just a few males around, like a mere afterthought. If there is no male to fertilise a haploid egg, such eggs can develop into males via haploid parthenogenesis'. The resulting males will participate in sexual reproduction (2).
Such menu of reproductive possibilities has made the Shield Shrimp so extraordinarily successful over the many million years.
The disadvantage of parthenogenesis, which produces an exact replica of the female, is a gene pool which remains static. It renders an organism unable to adapt to changing conditions. Sexual reproduction adds variety to the genes of a species - but also the danger of harmful mutations.
The shrimps have a bet both ways.
Among species which practise parthenogenesis are some starfish, worms and sea urchins, whiptail lizards and certain rattlesnakes (3).
Triops eggs are the faunal equivalent to the seeds of the drought avoiders, those ephemeral plants of the Simpson Desert which spend more time as seeds than as plants. For most of the time the existence of the species Triops is only a potential existence. In zones where intervals between rain may last for years, this is a very clever method to simply skip a chapter of time which is useless to the species.
Triops have answered ‘To be or not to be?' with ‘To be and not to be'.
Sources:
1) http://filebox.vt.edu/users/channum/triops_species.htm
2) www.limnology.org/news/28/arid_rivers.html
3) Dr. Karl S.Kruszelnicki (Sydney Morning Herald ‘Good Weekend' 1.10.05)
www.crustacea.net/crustace/www/notostra.htm
Encyclopaedia Britannica
‘The International Wildlife Encyclopedia' (Dr.Maurice Burton / Robert Burton)
‘Australia A Timeless Grandeur' Reg Morrison / Helen Grasswill
WEDGE-TAILED EAGLE (Aquila audax) got its epithet ‘audacious' because, when hunting in groups, it has been seen taking on animals like large kangaroos. But usually it hunts alone. It grows to just over 4 kg in weight (9 pounds), the female might get one kilogram heavier. Normally, the eagle does not prey on animals more than half its own weight.
With a wing span of a little over 2 metres (6.5 feet), the Wedge-tailed Eagle likes to ride air currents and can soar 2000m high (6650 feet). It is Australia's largest bird of prey, and the largest in the world after the American Condor. It is dark brown to black, and lighter the younger the bird. The legs are covered in feathers right down to the feet. In flight, the eponymous wedge in the tail shows up clearly.
Their home range extends from southern New Guinea to Tasmania, and from ground level to alpine heights. They prefer territory which can easily be overseen, like open or lightly wooded country and sclerophyll forest. They shun rainforest with its dense or closed canopy. In their territory they will nest in a prominent location with a controlling view which can be the top of a cliff or the tallest tree. Their nests are solid structures, almost 2 metres across (6.5 feet) and built by both sexes.
It may weigh up to 400kg (880 pounds) and is fussed about daily with fresh leaves and sprigs.
Eagles mate for life and stay monogamous. They are territorial and will defend their nest and its surrounding up to a radius of 4km (2.5 miles), but less if food resources are plenty.
They are very sensitive about their territory. Any changes to it, like land clearing, will cause them to leave their nest and look for new surroundings.
Breeding happens in winter, in the southern hemisphere any time between April and September. Males and females alternate incubating usually two, sometimes 3 eggs for 42 - 45 days. They are not laid in one go, but within an interval of up to 4 days. That means, the first hatchling has a natural advantage. It is the stronger one. It demands first serve at feeding time and often eats the younger, less developed sibling which might be starving. To rear only one young is quite the normal thing for eagles.
After leaving the nest the young remain with their parents for another 11 weeks. Then they move on. Some tagged ones have been traced 850km (530 miles) away.
The Wedge-tailed Eagle has been hunted in the hundredthousands. Graziers blamed it for killing lambs. But this might happen only on rare occasions. Probably, the lamb was dead before the bird got down to it. The eagle eats fresh carrion as well as live animals like rabbits, reptiles and smaller birds. A fresh road kill attracts a variety of preying birds. But when an eagle arrives all other birds step back.
The introduction of the rabbit was like a lottery win for the eagle. Observations attribute between 30% and 70% of the bird's diet to the rabbit. And at times, this has topped 90%.
Often, man's clearing of the country for grazing and pastoralism has benefitted the eagle which needs open land for hunting.
Today, in Australia the eagle is protected. Unfortunately, being also a carrion eater, the bird might go for a poisoned dingo or fox bait and die.
Rising sea levels at the end of the last ice age made Tasmania an island again about 10 000 years ago. The Tasmanian population of Wedge-tailed Eagles has been separated from the one on the mainland ever since. And they have evolved into a subspecies. There are an estimated 130 breeding pairs left on the island, and they are listed as endangered (1).
Sources:
1) www.dpiwe.tas.gov.au/inter.nsf/WebPages/SJON-573VB3?open
www.amonline.net.au/birds/factsheets/wedgetail.htm
www.nationalparks.nsw.gov.au/npws.nsf/Content/The+wedge-tailed+eagle
WHALES Southern Right Whale Eubalaena australis.
see: ‘NULLARBOR'