MONITORING WESTERN AUSTRALIA

The Pilbara is a region of Western Australia characterised by red sand, vast gorges and ancient landscapes. It is extremely remote and its most densely populated town, Karratha, is home to just 17,000 people. Although there are very few people in this 500,000 km2 exapanse of the outback, there are plenty of reptiles. Some of the most diverse reptiles that call the Pilbara home are the monitor lizards (Varanids). Locally referred to as ‘goannas’ the Pilbara hosts the smallest monitor lizards in the world and the largest lizard in Australia.

The Pilbara is famed for its biodiversity because it hosts such a wide range of habitats. The southern and central Pilbara is comprised largely of rocky escarpment and gravelly terrain, whereas the northern Pilbara is far sandier with acres of dry dunes stretching almost up to the coast. Intersecting these regions are deep gorges filled with permanent water that creates strings of oases through the barren landscapes. Occasional rainfall sustains grasslands with mulga trees and towering ranges leave in their wake dry spinifex country. Because of this, the Pilbara is an epicentre for endemism (animals that cannot be found anywhere else in the world). There are around 10 different species of monitor lizards in the Pilbara all occupying their ecological niches.

Of the Varanids, the first lizard that springs to mind when one mentions the Pilbara is the famous Pilbara rock monitor (V. pilbarensis) and its close relative the Hamersley rock monitor (V. hamersleyensis). The Pilbara rock monitor occupies rock escarpments around Chichester Gorge, while its cousin the Hamersley rock monitor occupies similar habitats further East around the Hamersley ranges. Both are small Varanids, rarely exceeding 50cm in total length, of which two thirds is comprised of the tail. They are very similar to the popular ‘Kimberley’ rock monitor, which is found further North in the subtropical Kimberley region and is frequently bred in captivity.

As well as the very tiny rock monitors, there are several reasonably large goannas in the Pilbara. These are the

Goulds (V. gouldii) and argus monitors (V. panoptes). Both can reach up to five feet in length and are extremely widespread and abundant across most of Australia. In fact, the Goulds monitor is one of the most widespread reptiles in Australia and can be found in just about any arid or semiarid environment. It also flourishes near human-inhabited areas where it scavenges on leftover foods. Although both the Gould’s and Argus monitors reach an impressive size, neither trumps the mighty Perentie (V. giganteus).

The Perentie is Australia’s largest lizard. It can grow over six feet in length and is amongst the top five largest lizards on earth, beaten only by the Komodo dragon (V. komodoensis), Asian water monitor (V. salvator) crocodile monitor (V. salvadorii) and has a similar size to the Nile monitor (V. niloticus). The Perentie is found across Western and central Australia, West of the Great Dividing Range. It is reasonably abundant but far shier than other large Varanids. It is, however, at the top of the food chain in outback Australia. It feeds largely on other reptiles, including the most venomous snakes on the planet. This lizard exemplifies intraguild predation as its diet is comprised mostly of other Varanids for which it competes for food. Perenties will frequently kill and eat small ridgetailed monitors (V. acanthurus) but also hunt adult Argus and Gould’s monitors too. Coastal populations will also frequently feed on sea turtle eggs.

Some of the more striking Varanids of Pilbara are the tiny arboreal species that thrive beneath the bark of dead mulga and she-oak trees. The pygmy mulga monitor (Varanus gilleni) rarely exceeds 35cm in length and belongs to the V. acanthurus complex. It is the second smallest species of monitor lizard in the world and can be found across most of the Pilbara region. Just above the Pilbara lies the Kimberleys, that play host to the smallest monitor species in the world, the Dampier Peninsular monitor (V. sparnus) – both belong to the Odatria subgenus that covers most of the small-bodied Varanids in Australia.

The Pilbara sits almost directly upon the Tropic of Capricorn. This is a latitudinal line that marks the southernmost point where the sun can be seen directly overhead. Further north lies the Tropic of Cancer, the most northern point where the sun can be seen directly overhead. Between these two lines is what people generally refer to as “the tropics.” Because this region experiences lots of sunlight, humid regions with heavy rainfall host tropical forests and drier areas produce harsh deserts. Ultimately, seasonality is generally reduced from four seasons in temperate regions to a distinct “wet” and “dry” in tropical regions (although some places experience multiple wet and dry seasons throughout the year). Simply put, the Pilbara is on the verge of tropical climates.

The Pilbara is also split into two halves. The northern half is characterised by soft red sand, whereas the interior is far more gravelly. This means that closely-related species have specific occupied niches within the broader geographical area. For example, woma pythons (Aspidites ramsayi) have evolved to burrow beneath the sand to hunt their prey and therefore occupy the North. Whereas, black-headed pythons (Aspidites melanocephalus) are far more terrestrial and therefore are more abundant in the south, where they can benefit from the harder, gravelly surface whilst hunting at night.

The gorges that run through the Pilbara and the Hamersley Ranges also create impressive microclimates, so when the tropical weather of the North reaches the Pilbara, the gorges fill with water. This creates impressive waterfalls and hosts the only sizeable amount of permanent water for hundreds of miles. This means that some species have evolved almost in isolation because of these mini, tropical oases. However, the threat of cane toads (Rhinella marina) that have already decimated reptile populations in the top end of Australia may pose a significant risk to biodiversity in the Pilbara. Currently, scientists believe that the cane toads will be unable to establish themselves within the Pilbara due to the immense amount of desert surrounding the gorges. However, similar things have been said about certain regions of the Kimberleys and West Queensland.

Furthermore, global warming is considered a major threat to all tropical ecosystems, but perhaps even more so to the areas that verge upon the tropics. Most rainfall in the Pilbara can be directly attributed to the tropical cyclones that hit the West Coast of Australia throughout April and May. Sadly, these cyclones are reported to be growing in intensity, travelling further inland and bringing with them more rain. How this will affect the region is yet to be known, but it may provide opportunities for cane toads to spread into the permanent waterways and gorges and potentially cause more flooding that could disrupt ecosystems.

Varanus acanthurus is perhaps the most kept monitor lizard in captivity. Its small size, active behaviour and reasonably simple care requirements make it an ideal candidate for herpetoculture. The ‘ackie’ is also one of the most abundant reptiles in the Pilbara. Being a generalist, it can occupy a range of habitats and even suburban environments. Chris Applin is a Varanid keeper who has bred various species of monitor lizards. He explained: “I would imagine ackies are the most popular of the Australian Varanids because of their generalist behaviours. Their range is massive! The ones in Alice Springs can tolerate temperatures lower than 10°C and higher than 50°C so there’s more room for error. Other Varanids, such as the Kimberley rock monitors (Varanus glauerti) can dehydrate very easily and require hot temperatures. A good parallel is the bredl's pythons (Morelia bredli), they can be kept really hot or really cold, but if you did that with a jungle carpet python (Morelia spilota cheynei), it would soon die. Ackies are awesome monitors. They should be as popular as beardies! Back in the day when I kept them, there weren’t many people working with them so they were just too expensive. Nowadays, I think more people are working with them so there’s no reason why they shouldn’t be as popular as beardies one day.”

Being monitor lizards, “ackies” are extremely inquisitive and active lizards. Although they spend a lot of time curled up beneath rocks to escape the dryness of the Australian desert, they are extremely agile and active hunters that will dart between rock crevices and spinifex mounds in search of insects. Ackie monitors have been kept in captivity for decades now. Over that time various localities and lines have been bred, giving keepers a variety of choices.

“There are a few different localities of ackie monitors in the Pilbara” adds Chris. “In the Northwest, there are the red varieties, but as you move towards central Australia and into the Northern Territory, the yellow varieties become more abundant. It’s the yellow ackies that are most common in the trade, although I suspect by now most captive-bred individuals will be mixed. You can get some red ackies that have been kept reasonably distinct from the mix of yellows and reds. The ‘Hendrick’ line of red ackies is the most similar to the wild types found in the Pilbara. A few people are breeding those, so keepers can source both varieties.”

There is much speculation around the distinction of various monitor lizards in Australia at species, subspecies and locality levels. Currently, there are three recognised subspecies of Ackie monitor, V. acanthurus acanthurus, V. acanthurus insulanicus and V. acanthurus brachyurus. The latter of the three is thought to be a distinct species, while the former is split by distribution. V. acanthurus acanthurus is found in the Kimberleys and North Pilbara, while V. acanthurus insulanicus has a more central distribution. “It’s a bit dubious as to whether the ackies should be different subspecies” added Chris. “The paper that was published wasn’t very thorough and in my opinion, all ackie monitors should be acanthurus acanthurus. The yellow-throated ackies are now acanthurus insulanicus. There are a few slight differences that are noticeable in captivity. Red ackies tend to bite a bit more, have a larger head, grow a little larger and have more of a spiny tail than the yellow ackies. I’ve always considered them slightly different because of that split, but I wouldn’t say that mixing them is a bad thing. Their care is certainly the same!”

Ackies require reasonably large vivariums that allow them to enact their active behaviours. In the wild, ackies are generalists but seem to prefer a region between rocky escarpments and spinifex country. Chris describes it as “rocky grassland.” A suitable setup should have plenty of hiding opportunities and décor that allows the animal to wedge itself between hides. These monitors use thigmotaxis to feel secure and to heat their bodies without exposure to predators. Whilst a suitable basking spot is essential, keepers must be very strategic with their décor placement. Furthermore, a naturalistic substrate such as ProRep Beardie Life is all but essential for allowing Ackies to dig and burrow in a manner that they would in the outback.

More advanced keepers, as well as breeders, must also enact some very minor seasonal fluctuations. Although not every population of Ackie monitor will be exposed to notable seasonality, those in the far north or the coastal regions of their distribution will experience drastic changes throughout the year. “I think a lot of keepers are now providing a temperature drop” adds Chris. “It gets pretty cold, even in the Pilbara. The guys that herp over there are not finding active animals in the winter. I think it would be best for keepers to drop the temperatures in winter and reduce their feeding slightly. It is good for breeding but also to stop them burning out generally.” Winter temperature drops are essential for some animals (mostly desert species) and beneficial for a vast range of reptiles as it encourages the males to go through spermatogenesis, which aids in fertility.

Chris added: “I’ve also been a big supporter of UV. There are people out there that have successfully kept monitors without UV but I just don’t get it. If you can give it, why wouldn’t you? Especially for monitors! They’re out in the day! I didn’t take any UV readings in Australia but I can tell you, it’s pretty high! Monitor lizards need a good quality UV lamp that gives out a lot of UV.” Perhaps the best way to provide UVB and appropriate heating for an ackie monitor is with a Ferguson Zone 3 T5, alongside a suitable spot bulb and infrared heat projector. They must be positioned in such a way that an adequately sized “patch” of sunlight is created within the vivarium.

Highly safe and effective disinfectants and treatment products for optimal hygiene and infection control. F10 has the product for your health and hygiene needs. f10products.co.uk