In 2017 and 2018 I walked the equivalent of 28 marathons in the scorching Western Australian outback. Why, you ask? To assess how some of Australia’s largest lizard species interact with restored mines.
As part of my PhD research, I hiked in often extreme heat on a mine site in WA’s sparsely populated Mid West region. My fieldwork was both physically and mentally demanding, as I spent many hours each day walking through the bush looking for signs of monitor lizards.
Being in a remote location and mostly alone, I had plenty of time to ponder the wisdom of my career choice, particularly on days when temperatures exceeded 40℃ and not even the lizards ventured from their homes.
Pushing through these mental challenges was difficult at times, but my work has provided me with some of my most rewarding experiences. And what I discovered may be crucial for restoring habitats destroyed by mining.
Habitat loss is a leading cause of biodiversity loss worldwide. Although mining typically has a smaller environmental footprint than other major industries such as agriculture or urbanisation, roughly 75% of active mines are on land with high conservation value.
There are around 60,000 abandoned mines in Australia, but very few of them have been officially closed. How to restore them is a growing public policy problem.
Recovering biodiversity can be an exceptionally challenging task. Animals are vital to healthy ecosystems, yet little is understood about how animals respond to restored landscapes.
In particular, reptiles are often overlooked in assessments of restoration progress, despite playing key roles in Australian ecosystems.
I wanted to know whether restored habitats properly support the return of animals, or whether animals are only using these areas opportunistically or, worse still, avoiding them completely.
To study how reptiles behave in restored mining areas, I hand-caught and tracked a young adult perentie. The perentie is Australia’s largest lizard species, growing to around 2.5m in length, and is an apex predator in arid parts of the country.
I tracked the lizard for three weeks to determine whether it was using the restored area, before the tracker fell off during mating.
Previous methods of tracking assume the animal used all locations equally. But I used a new method that measures both the frequency with which animals visit particular places, and the amount of time they spend there. This provided a valuable opportunity to assess how effective restoration efforts have been in getting animals to return.
My research, published this week in the Australian Journal of Zoology, shows that while the perentie did visit the restored mine, it was very selective about which areas it visited, and avoided some places entirely. The lizard went on short foraging trips in the restored mine area, but regularly returned to refuge areas such as hollow logs.
This is because hot, open landscapes with minimal refuges present high risks for reptiles, which rely on an abundance of coverage to regulate their body temperature and to avoid predators. Such costs may make these areas unfavourable to reptiles and limit their return to restored landscapes.
In comparison, undisturbed vegetation supported longer foraging trips and slower movement, without the need to return to a refuge area. Unfortunately, areas undergoing restoration often require exceptionally long time-periods for vegetation to resemble the pre-disturbed landscape.
Restored landscapes often lack key resources necessary for the survival of reptiles. As vegetation can require a long time to reestablish, returning fauna refuges like hollow logs and fauna refuge piles (composed of mounds of sand, logs, and branches) could be crucial to aiding in the return of animal populations.
My research team and I have called for animals to be considered to a greater extent in assessments of restoration success. In the face of increasing rates of habitat destruction, we need to understand how animals respond to habitat change and restoration.
Failing to do so risks leaving a legacy of unsustainable ecosystems and a lack of biodiversity.
Only fish have gills, right? Wrong. Meet Hydrophis cyanocinctus, a snake that can breathe through the top of its own head.
The 3m species, which is native to Australian and Asian coastal waters, can draw in oxygen with the help of a unique set of blood vessels below the skin in its snout and forehead.
The network of blood vessels works very similarly to a fish’s gills, and represents a newly discovered addition to the extraordinary range of adaptations that sea snakes use to thrive below the waves.
In evolutionary terms, sea snakes are relative newcomers to aquatic life, having evolved from land-based snakes only about 16 million years ago. This is much more recent than marine mammals such as whales and dugongs, which arose around 50 million years ago.
The roughly 60 known species of sea snakes have nevertheless developed an impressive array of adaptations to marine life. These include salt glands under the tongue, nostrils that face upwards and can be sealed by valves, paddle-like tails to facilitate swimming, and the ability to absorb oxygen and eliminate carbon dioxide through their skin.
Some sea snakes have even evolved light sensors on the tips of their tails, possibly as a way to avoid having them nibbled off by predators when partially hidden in crevices.
Just when we thought we had uncovered all the strange things sea snakes do, we discovered something new. As we report today in the journal Royal Society Open Science, the annulated sea snake Hydrophis cyanocinctus effectively has a set of gills on its forehead.
The first sign of something unusual was an odd hole (in anatomical terms, a “foramen”, the Latin word for “hole”) in the roof of this species’ skull.
This hole is reminiscent of the “pineal foramen” found in several lizard species, which contains a tiny light-sensitive organ called the pineal eye. Could sea snakes also have a pineal eye?
No trace of such a foramen has ever been found in a modern snake. In fact, snakes are thought to have lost the pineal foramen at least 100 million years ago, which is the age of the oldest reasonably complete fossil snakes.
However, because some sea snakes have light-sensitive organs in their tails, we couldn’t rule out the possibility of a light-sensitive organ reappearing in its ancestral position in the skull – snakes did evolve from lizards, after all.
We decided to investigate this unexpected foramen in H. cyanocinctus more closely. We obtained some live specimens from Vietnam, where sea snakes are commonly sold as food in fish markets, and generated images of the soft tissues around the foramen using a combination of traditional and computer-assisted methods.
These images revealed that this snake does not have a pineal eye. What actually goes through the mysterious hole in its skull is a large blood vessel (sometimes paired). This blood vessel then travels forward and branches into a complex network of veins and sinuses immediately under the skin of the forehead and snout.
We then examined other snakes, both terrestrial and marine, using the same methods, and realised that this network of blood vessels in H. cyanocinctus is unique.
Did snakes evolve from ancient sea serpents?
While a network of blood vessels is expected to be present under the skin of all snakes, what is special about H. cyanocinctus is the greatly exaggerated size of the blood vessels and the fact that they converge towards a single large vein that goes into the brain.
This strange network of blood vessels makes sense when we consider that sea snakes can breathe through their skin. This happens thanks to arteries containing much lower oxygen concentrations than the surrounding seawater, which allows oxygen to diffuse through the skin and into the blood.
However, these low oxygen levels in arterial blood can cause problems, because the brain may not get the oxygen it needs. The dense network of veins on the forehead and snout of these sea snakes helps solve this problem by picking up oxygen from seawater and redistributing it to the brain while swimming underwater.
If you think that sounds similar to what fish do with their gills, you’re absolutely right. H. cyanocinctus has managed to evolve a respiratory system that works in much the same way as gills, despite the vast evolutionary distance between these two groups of species. Truly, these snakes are indeed creatures of the sea.
For nine hours, my colleague Michael Shackleton and I held onto our scooters for dear life while being slapped in the face by spiked jungle plants in the mountains of Cambodia. We only disembarked either to help push a scooter up a slippery jungle path or to stop it from sliding down one.
With our gear loaded up on nine scooters – 200 metres of fishing nets, two inflatable kayaks, food for five days, hammocks, preservation gear for collection of DNA, and other assorted scientific instruments – we at last arrived at one of the few remaining sites known to harbour the critically endangered Siamese crocodiles.
The Siamese crocodile once lived in Southeast Asian freshwater rivers from Indonesia to Myanmar. But now, fewer than 1000 breeding individuals remain.
In fact, during the 1990s the species was thought to be completely extinct in the wild. Then, in 2000, scientists from Fauna and Flora International found a tiny population in the remote Cardamom Mountains region of Cambodia.
We travelled to this remote wilderness in 2017 to determine habitat suitability for the reintroduction of captive-bred juvenile Siamese crocodiles. We wanted to understand the food web there to see whether it contains enough fish to sustain the young crocs.
Our journey would not have been possible without the help of Community Crocodile Wardens – local community members who patrol the jungle sanctuaries for threats and record crocodile presence. Wardens also conduct crocodile surveys further afield to discover new populations or to identify new areas of potential suitable crocodile habitat for juvenile releases.
Our recent study found to ensure the species survives, reintroduction locations must be protected from fishing pressure – both from a food supply perspective, but also from risk of entanglement in nets.
When we arrived at our site, northwest of the village of Thmor Bang, our day was capped by what we came to know as the standard evening downpour, despite assurances that we had, in fact, timed our trip for the dry season.
Kayaks were inflated, nets set, and sampling was underway. This proved laborious – to ensure crocodiles didn’t drown, we couldn’t leave nets unattended in the water overnight, but instead checked them every hour until morning.
Siamese crocodiles are generally not aggressive to humans, but they come into conflict with people when caught in fishing nets.
This often leads to the crocodile drowning and the fishing net being ruined. It’s a disaster on both counts, because fish is the only source of protein for many local communities in Cambodia.
Like many other apex predators around the world, the Siamese crocodile is also in decline because of habitat destruction and poaching for their skins.
Their potential large size and generally placid nature means they are highly prized by crocodile farmers who use the skins for handbags and footwear. Crocodile farmers also often hybridise the Siamese crocodiles with other non-native crocodile species.
This means programs for Siamese crocodile reintroduction and breeding must carefully genetically screen all young crocodiles bred in captivity to make sure they’re not actually hybrids, so the “genetically pure” wild populations can remain.
Despite a pretty good understanding of captive Siamese crocodile behaviour and biology, very little is known about Siamese crocodiles in the wild, such as what they eat or how much food they need to raise an egg to adulthood.
Our only reliable indication of diet comes from scats (crocodile poo or “shit of croc” as we came to call it) collected along the river banks inhabited by remnant populations.
Carefully collected poo samples containing scales and bones tell us fish and snakes make up a significant proportion of the Siamese crocodile diet.
But the shrouded, mystical, extremely remote and virtually inaccessible jungle in the Cardamom Mountains has ensured we know next to nothing about fish communities within habitats set for the release of captive crocodile. And this information is particularly important for prioritising release locations for captive bred juveniles.
We spent four days sampling fish communities and then repeated the process at two other equally remote locations within the Cardamoms, requiring two days travel between each.
We saw groups of gibbons moving through the forest and macaques climbing down from trees to drink at the river. But at last we spotted a wild Siamese crocodile after dark, swimming in our morning bathing pool, on our second-last day.
Ultimately, we distinguished 13 species of fish from the Cardamom Mountains, confirming the presence of two previously unconfirmed species groups for the region.
What’s more, we found fish density was highest in areas with more Siamese crocodiles, and lowest in areas with more human fishing pressure.
Understanding the food web of crocodile reintroduction sites is important, because conservation managers need to understand the ecological carrying capacity of the system – the number of individual crocodiles that can be supported in a given habitat. Learning this is especially important when historical information does not exist.
Preservation of fish stocks within Siamese crocodile habitats is critical for survival of the species. But a key challenge for natural resource managers of the Cardamom Mountains is balancing crocodile density with local fishing necessity, and to do this, we need more information on Siamese crocodile biology.
You may have seen news in recent days of the suspected demise of the Victorian grassland earless dragon – now thought to be the first lizard species to be driven to extinction by humans in mainland Australia.
That suspicion arose on the basis of a newly published study in Royal Society Open Science by our research team, in which we discovered that the grassland earless dragons of southeastern Australia are not a single species, but four distinct ones: one that lives around Canberra, two in New South Wales, and one restricted to the Melbourne region.
The most recent confident sighting of the Melbourne species was 50 years ago, in 1969 – hence the fears that the Victorian species has already succumbed.
But despite this worrying news, we’re not leaving this lizard for dead just yet. Conservationists are now combing remaining grassland around Melbourne in a search for survivors.
Although no lizard species have previously been declared extinct on the Australian mainland, the grassland earless dragons (Tympanocryptis) of southeastern Australia have long been the subject of conservation concern. Even before being split into four separate species, they were already officially listed as endangered.
The Victorian grassland earless dragon (Tympanocryptis pinguicolla) is known only to occur in the native grasslands around Melbourne. A review of historical collections at Museums Victoria show that it was found at several locations including Sunbury, Maribyrnong River (then called “Saltwater River”), and as far west as the Geelong area until the late 1960s.
Although there is little information available about the ecology of this species, it was described by Lucas and Frost in 1894 as:
Inhabiting stony plains and retreating into small holes, like those of the ‘Trap-door Spider,’ in the ground when alarmed […] Often met with under loose basalt boulders.
The last confirmed sighting was near Geelong in July 1969.
Globally, 31 reptiles have been listed as extinct or extinct in the wild, according to the IUCN Red List, the global authority on the status of species. Two skinks and one gecko species have been declared extinct in the wild on Christmas Island, a remote Australian territory in the Indian Ocean. But until now there have been no recorded reptile extinctions on the Australian mainland.
Yet it is too early to give up on the Australian grassland earless dragon. Zoos Victoria researchers have completed a mapping analysis of potential grassland habitats. But this doesn’t give us enough information to say whether or not any grassland earless dragons remain.
There are several factors that leave open the possibility that the Victorian grassland earless dragon is still clinging to survival. There are some remaining habitat areas that have not yet been surveyed, and this species is small, secretive and hard to find. We urgently need more surveys to try and find any remaining populations.
If these lizards are not yet extinct, their protection will clearly become an urgent conservation priority. But it is hard to develop a conservation program without knowing where the target species actually lives, or indeed whether it is still alive at all.
Zoos Victoria is now leading a campaign, alongside expert ecologists and local communities, to try and confirm the presence or absence of the Victorian grassland earless dragon. This involves various methods, including habitat mapping, camera trapping, and active searching. The team is also working to identify unsurveyed areas that might potentially be home to these elusive lizards.
Last year the team deployed a series of small pitfall traps at two locations in Little River. Unfortunately, no earless dragons were detected during the survey and few lizards of any species were caught, despite the fact that these locations seemed to offer appropriate food and habitat.
The team is not giving up yet and is committed to continuing the search, with Zoos Victoria researchers having identified sites with suitable habitat both within and outside of the historical distribution, which they aim to survey intensively over the coming years. Meanwhile, reptile keepers at Zoos Victoria are developing husbandry techniques to help look after the grassland earless dragon species from Canberra and NSW.
The conservation challenge has got harder, because where previously we were tasked with looking after one species, we now have to safeguard at least three – and hopefully four!
This article is based on a blog post that originally appeared here. It was coauthored by Adam Lee and Deon Gilbert of Zoos Victoria.
For most animals, reproduction is straightforward: some species lay eggs, while others give birth to live babies.
But our recent research uncovered a fascinating mix between the two modes of reproduction. In an Australian skink, we observed the first example of both egg-laying and live-bearing within a single litter for any backboned animal.
This suggests some lizards can “hedge their bets” reproductively, taking a punt on both eggs and live-born babies to improve overall survival chances for offspring.
Most vertebrate species (animals with a backbone) fall neatly into one of two distinctly different reproductive categories.
Oviparous species are egg-layers. These eggs may undergo external fertilisation – such as in spawning fish – or are fertilised and shelled internally, like those of reptiles and birds. Oviparous embryos rely on egg yolk as a source of nutrition to continue development until hatching.
In contrast, viviparous species are live bearers that carry their young to term. Some live-bearing species, including humans, support embryonic development internally via a placenta. Egg-laying is ancestral, meaning that modern live-bearers have descended from egg-laying ancestors.
Physiologically, the evolution of live birth from egg-laying is no mean feat. This transition requires a whole suite of changes, sometimes including the evolution of a placenta – an entirely new specialist organ – as well as loss of the hard outer eggshell, and keeping the embryo inside the body for a longer time.
Despite these complex steps, reptiles, particularly snakes and lizards, appear to be unusually predisposed to making the leap to live birth. This capacity has evolved in at least 115 groups of reptiles independently.
It’s easy to see why reptiles, as a group, are fascinating models for studying how live birth evolves from egg-laying.
Of particular interest are two Australian skinks that have both live-bearing and egg-laying individuals (known as being bimodally reproductive). These lizards are incredibly valuable to evolutionary biologists as they offer a snapshot into evolutionary processes in action.
The three-toed skink Saiphos equalis is one such species. Reproduction in S. equalis varies geographically: populations around Sydney lay eggs, while those further north give birth to live young.
Whether individuals are live-bearing or egg-laying seems to be genetically determined: when researchers swap their environmental conditions (by moving them from one site to another), the females retain their original reproductive strategy.
Our latest research shows this lizard is intriguing in another completely unexpected way.
We observed a live-bearing female that laid three eggs, and then gave birth to a living baby from the same litter weeks later. We incubated two of the eggs, one of which hatched to produce a healthy baby.
This finding is remarkable for two reasons. First, as far as we are aware, this is the first example of both egg-laying and live birth within a single litter for any vertebrate.
Second, in some cases, individuals may be capable of “switching” between reproductive modes. In other words, as laying eggs and giving birth each come with their own advantages and disadvantages, individuals may be able to “choose” which option best suits the current situation.
To better understand this reproductive phenomenon, we investigated the structure of the egg coverings of these unusual embryos in minute detail (using an advanced technology called scanning electron microscopy).
We found that in this litter, the egg-coverings were thinner than those of normal egg-laying skinks and had structural characteristics that overlapped with those of both egg-layers and live-bearers (which have thinner coverings that are greatly reduced).
We still don’t know the trigger that caused this female to lay eggs and give birth to a live baby from the same pregnancy.
However, our findings suggest that species “in transition” between egg-laying and live bearing may hedge their bets reproductively before a true transition to live birth evolves.
Being able to switch between reproductive modes may be advantageous, particularly in changing or uncertain environments.
For example, extreme cold, drought or the presence of predators can be risky for vulnerable eggs exposed to the environment, meaning that mothers that can carry offspring to term may have the upper hand.
In contrast, lengthy pregnancies can be taxing on the mother, so depositing offspring earlier as an egg may be beneficial in some situations.
We suggest that other species in which live birth has evolved from egg-laying relatively recently may also use flexible reproductive tactics.
Further research into this small Australian lizard, which seems to occupy the grey area between live birth and egg-laying, will help us determine how and why species make major reproductive leaps.
We are all familiar with the concept of “fake news”: stories that are factually incorrect, but succeed because their message fits well with the recipient’s prior beliefs.
We and our colleagues in conservation science warn that a form of this misinformation – so-called “feelgood conservation” – is threatening approaches for wild animal management that have been developed by decades of research.
The issue came to a head in February when major UK-based retailer Selfridges announced it would no longer sell “exotic” skins – those of reptile species such as crocodiles, lizards and snakes – in order to protect wild populations from over-exploitation.
But this decision is not supported by evidence.
Banning the use of animal skins in the fashion industry sounds straightforward and may seem commendable – wild reptiles will be left in peace, instead of being killed for the luxury leather trade.
But decades of research show that by walking away from the commercial trade in reptile skins, Selfridges may well achieve the opposite to what it intends. Curtailing commercial trade will be a disaster for some wild populations of reptiles.
How can that be true? Surely commercial harvesting is a threat to the tropical reptiles that are collected and killed for their skins?
Actually, no. You have to look past the fate of the individual animal and consider the future of the species. Commercial harvesting gives local people – often very poor people – a direct financial incentive to conserve reptile populations and the habitats upon which they depend.
If lizards, snakes and (especially) crocodiles aren’t worth money to you, why would you want to keep them around, or to protect the forests and swamps that house them?
The iconic case study that supports this principle involves saltwater crocodiles in tropical Australia – the biggest, meanest man-eaters in the billabong.
Overharvested to the point of near-extinction, the giant reptiles were finally protected in the Northern Territory in 1971. The populations started to recover, but by 1979-80, when attacks on people started to occur again, the public and politicians wanted the crocodiles culled again. It’s difficult to blame them for that. Who wants a hungry croc in the pond where your children would like to swim?
But fast-forward to now and that situation has changed completely. Saltwater crocs are back to their original abundance. Their populations bounced back. These massive reptiles are now in every river and creek – even around the city of Darwin, capital of the Northern Territory.
This spectacular conservation success story was achieved not by protecting crocs, but by making crocs a financial asset to local people.
Eggs are collected from the wild every year, landowners get paid for them, and the resulting hatchlings go to crocodile farms where they are raised, then killed to provide luxury leather items, meat and other products. Landowners have a financial interest in conserving crocodiles and their habitats because they profit from it.
The key to the success was buy-in by the community. There are undeniable negatives in having large crocodiles as neighbours – but if those crocs can contribute to the family budget, you may want to keep them around. In Australia, it has worked.
The trade in giant pythons in Indonesia, Australia’s northern neighbour, has been examined in the same way, and the conclusion is the same. The harvest is sustainable because it provides cash to local people, in a society where cash is difficult to come by.
So the evidence says commercial exploitation can conserve populations, not annihilate them.
Why then do companies make decisions that could imperil wild animals? Probably because they don’t know any better.
Media campaigns by animal-rights activists aim to convince kind-hearted urbanites that the best way to conserve animals is to stop people from harming them. This might work for some animals, but it fails miserably for wild reptiles.
We argue that if we want to keep wild populations of giant snakes and crocodiles around for our grandchildren to see (hopefully, at a safe distance), we need to abandon simplistic “feelgood conservation” and look towards evidence-based scientific management.
We need to move beyond “let’s not harm that beautiful animal” and get serious about looking at the hard evidence. And when it comes to giant reptiles, the answer is clear.
The ban announced by Selfridges is a disastrous move that could imperil some of the world’s most spectacular wild animals and alienate the people living with them.
Daniel Natusch, Honorary Research Fellow, Macquarie University; Grahame Webb, Adjunct Professor, Environment & Livelihoods, Charles Darwin University, and Rick Shine, Professor in Evolutionary Biology, University of Sydney