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Friday, 31 May 2013

Goanna, Go!

Australia has truly been described as the land of lizards, with central Australian spinifex hummock grasslands containing over 400 lizards per hectare, with over 40 species co-existing. They are both predators and prey in an ecosystem where the spinifex supports a vast biomass of grazing termites, which fill the role of antelopes in the African plains. The top predators - the lions if you like - in this system are goannas of the family Varanidae. They don't generally stoop to eating termites, but they eat many smaller animals which do. 
Sand Goanna Varanus gouldii north of Bourke, New South Wales.
This familiar species is found across virtually the whole continent, missing only from the far south-east and north-east.
Elsewhere in their wide range - across Africa and southern Asia - they are generally known in English as monitors, allegedly for their supposed habit of 'warning' of the presence of crocodiles. In Australia however (where varanids have reached the peak of their diversity) the British colonists, who certainly weren't herpetologists, confused them with New World iguanas; the quintessentially Australian 'goanna' is a corruption of that. However, we're a perverse lot, and some local species are still called 'monitors'...
Lace Monitor V. varius, Finch Hatton Gorge, near Mackay, tropical Queensland.
This is probably the best-known Australian goanna, being found right along the east coast where most people also live.
It's a big animal, up to two metres long, and can be a tad intimidating around camps and picnic areas.
It seems that the goannas are more closely related to snakes than to other lizards, though this is not universally accepted. One thing that goannas and snakes have in common, only recently recognised, is the presence of venom in the mouths of varanids (and iguana relatives), and other work proposes that this supports the idea of a common ancestor for all three groups. To date most of the work on this relates to the huge Komodo Dragon V. komodoensis of Indonesia; venom flows from glands between the front teeth into wounds made by the animal's ferocious bite. There have long been stories in Australia that goanna bites "never heal"; it was supposed that this relates to a diet that includes carcasses and poor dental hygiene, but there may be more to it than that. These venoms are relatively low-potency and slow acting; it seems that the large victim is simply patiently followed, perhaps for days, until it weakens.

Goannas and snakes (and at least some other lizards) make use of Jacobson's Organs, a pair of sensory organs located above the roof of the mouth; while not unique to goannas, they are particularly well-developed in them and are doubtless very significant. Chemicals in the air are transferred by the tongue to the organ via ducts; this sense (perhaps best thought of by those of us without them as 'smell-taste') appears to supplement scent.
Yellow-spotted Goanna Varanus panoptes, Bladensburg National Park, Queensland.
The forked tongue - another goanna characteristic reminiscent of snakes - flicks constantly in and out, 'tasting' the air.
This species is found across much of north-east and north-west Australia, but where the introduced poisonous Cane Toads have invaded, numbers have crashed. Fortunately for this individual (investigating our camp) the toads
haven't entered this drier environment.
The largest goanna that lived only left the scene some 40,000 years ago, well within the time of human occupation of Australia. Megalania prisca (sometimes called Varanus priscus) may have been up to seven metres long and weighed well over a tonne; I would not have argued the occupation of a campsite with that one! Moreover it is within the venom-bearing group, and lived long after that group split up, so would have probably been the largest venomous animal ever to live.
Yellow-spotted Goanna in camp, Bladensburg NP.

Goannas are now the top predators in most of Australia (leaving aside the recently-introduced Dingo); indeed it has been suggested - I hope in jest! - that marsupials don't need a very big brain to stay a jump ahead of a reptile... Indeed these reptiles show intelligence in locating and accessing prey; they dig out burrows, either of mammals or scorpions, and climb readily. For both activities, their enormous claws are extremely efficient.
Yellow-spotted Goanna, Bladensburg NP; note huge claws.

They are the bane of the lives of tree hollow-nesting birds, which will attack them fiercely, but often with little effect. Many species will also take to the trees when threatened; plenty of stories also tell of them running up the nearest tall object in such a situation, including a person, though first-hand accounts are harder to find...

Lace Monitor on ironbark, Pilliga State Forest, New South Wales.
They effortlessly descend head-first.

All lay leathery eggs; some seal them in termite mounds where the controlled temperature and humidity is perfect for them. There is now evidence that the female of these species returns at just the right time to break open the mound again and release the hatchlings. 

Goannas are an integral part of Australia, through every part of which they still swagger with an inimitable insouciance, and I for one am glad of it.
Sand Goanna, above, and Yellow-spotted Goanna, below.


Tuesday, 28 May 2013

Desert Oaks; beautiful desert giants

If I were to ask you to nominate Australia's most photographed tree, I wonder what you'd suggest? Perhaps the Cazneaux Tree (a River Red Gum in the southern Flinders Ranges, made famous by Harold Cazneaux's 1937 photograph The Spirit of Endurance, and rephotographed numerous times since)? Or maybe the Curtain Fig at Yungaburra on the Atherton Tablelands of north Queensland, a massive Strangler Fig visited by every tourist bus in the area, and there are many of them!
A segment of the Curtain Fig Ficus virens, Yungaburra, a massive tree.
You'll probably have other suggestions, but my bet is on a tree that most people don't even realise they're photographing. 

Every day hundreds of people gather in central Australia at set areas to watch the sun going down on mighty Uluru, previously known for a while to English speakers as Ayer's Rock. The viewing areas are extensive, so there's no real sense of crowding, and the tour buses use a different area from private cars. A couple of weeks ago we joined them. Here is a selection of photos, taken over a 40 minute period from before to after sunset - just five of 18 that I ended up keeping.

So, if every one of the people there on just that one evening took that many pictures - and many would have taken far more - that's thousands of pictures a day, and it's not peak visiting season yet.

And, you see the tree? I suspect that most photographers don't even really notice it. Here it is again closer up, the shots taken just 10 minutes apart - the light changes are truly stunning.

This tree - my nomination for the title of Most Photographed Tree in Australia - is a Desert Oak, Allocasuarina decaisneana. It is my favourite tree species of the Australian central-western deserts, limited to an area of eastern Western Australia, south-western Northern Territory and a tiny bit of north-western South Australia. They are the only casuarinas in central Australia, most of the family being near-coastal in distribution. (Some time ago the genus Casuarina was controversially split into two, creating the genus Allocasuarina based on minor differences.)

It has adapted to life in the sandy dune country, where spiny spinifexes (hummock grasses of the genus Triodia) dominate the understorey.
Desert Oaks, Chambers Pillar, Northern Territory.
Unlike many other casuarinas, adult Desert Oaks are largely fireproof, recovering from epicormic shoots in the crown; at the same time seedlings sprout in the wake of the fire.

Stand of Desert Oaks south of Alice Springs.
In the photo above the beautiful adult trees appear to be growing above another bottle-brush-shaped species, but this is an illusion. The seedlings don't resemble the adult trees at all.
Desert Oak seedlings, Uluru - Kata Tjuta National Park.
Close to the ground the young trees are a spiky tangle, resisting grazing. The crown doesn't form for years; during this time the emphasis is on sending a tap root deep into the soil. When it strikes ground water many metres down, the crown finally develops and the side branches wither. 

The timber is hard and heavy and was used by the desert peoples for tools and weapons but, perhaps fortunately, it doesn't hold its shape after cutting and drying, so wasn't harvested by European settlers.

The species name honours a Belgian botanist, Joseph Decaisne, who spent his working life - much of the 19th century - working in Paris, especially at the Muséum d'Histoire Naturelle, where he began as an apprentice gardener. He never visited Australia, though he described some species from French expeditions returning from there. He rose to become regarded as the leading French botanist of his time, though it is often said that it was his studies into fruit varieties which were his main achievement. It was the great German-Australian botanist Ferdinand von Mueller who honoured Decaisne with the name.

There are separate male and female flowers but, unlike in many casuarinas, they occur on the same tree. The seed cones are magnificent, and can be up to 10cm long.
Desert Oak seed cones.
One day I'll do a posting on casuarinas in general, but for today I wanted to focus on this one beautiful species. 

Meantime, do you have another nomination for most-photographed tree? I'd love to hear.

There will be more postings inspired by the wonderful arid lands we've just visited; thanks for waiting for me!