Australian Wildlife Ep 2: Reptiles
Australian Wildlife Episode 2 Reptiles
Before we begin: what makes a reptile a reptile? What are some of the defining traits that they share?
Well, they are ectothermic, meaning that they are unable to maintain a constant internal body temperature themselves. They must instead rely on external heat sources, for example sunlight or hot rocks or concrete, to keep warm. Which is why you’ll often see them basking in the sun.
Ectotherms are often referred to as “Cold-blooded”, but this isn’t technically true, as their blood isn’t cold, it’s just kept warm in a different way.
Another major characteristic of reptiles is that their skin is covered in scales. The scales are hard plates, used for protection, which grow out of their skin. They are made of a protein called Keratin, which is also the key structural material in hair, nails and feathers. But of course, reptiles aren’t the only animals with scales. They are also found on fish, some mammals like armadillos and even the feet of birds.
Lets start things off with: LIZARDS
Bet you’ve never seen anything quite like this. This is the Frilled-Neck Lizard!
Also known as the Frilled Lizard, or frilled dragon, this carnivorous reptile can live up to 20 years and grow to a 85cm. They are found across northern Australia and southern New Guinea and spend most of their time camouflaged on tree trunks and branches, coming down only to feed or mate.
Their name comes from the colourful skin flap encircling their heads, which can be yellow, orange or red depending on distribution. When threatened, they extend their frill, giving the illusion that they’re much larger than they are, hopefully scaring off their enemies. But if this fails, they will simply sprint away. Defense isn’t all the frill is used for! It can also be used for communication, finding a mate and when sunbathing - they extend it out in order to absorb greater amounts of heat, so it’s useful in thermoregulation (remember, they’re ectotherms).
They mainly feed on insects (meaning they are primarily insectivores) but they are also known to eat spiders, mice and other lizards.
Once the female lays eggs, the sex of the offspring (known as hatchlings) is determined by temperature. Warmer temperature means more males while cooler means more females.
Blue Tongued Lizard
This unique lizard can be found in most habitats, across much of eastern and northern Australia. Like the frilled-neck lizard, they rely on the sun for thermoregulation.
As the name would suggest, Eastern Blue-tongue Lizards process a vivid blue tongue, which they use as a defense tool to scare off predators. When threatened, they open their mouth and hiss. The bright blue is a stark contrast against the rest of their pink mouth.
They have grey or brown bodies, with darker bands running along their torsos and tails and are much lighter on their bellies. They have a wide, triangular head and can grow up to 60cm.
They hunt for their prey (mainly insects and snails) using a specialised organ on the roof of their mouths known as a “Jacobson’s Organ”. This is used to sense chemicals emitted by their prey. They are omnivorous and also eat vegetation and berries.
Female lizards do not lay eggs, instead they produce live young. They give birth to 10-25 young in a litter and are self-sufficient at birth.
Let’s move on to my favourite animals: Turtles!
I’ll start by clarifying the difference between a turtle and a tortoise. While both have hard shells, tortoises are adapted for life on land, while turtles have adapted for life in the water. Tortoises have a more rounded, dome shape to their shells, while turtles have flatter, more streamlined shells for swimming through water. Tortoises have thick, club-like legs and feet, to support their weight on land, while turtles have flippers or webbed feet for swimming through the water. We’ll concentrate on turtles as there are no Tortoises endemic to Australia.
We’ll start with a freshwater species, the Murray River Turtle
They also go by the names Murray short-necked turtle or Macquarie turtle.
Their shells are a medium to dark brown on top and a yellowy-cream colour underneath.
They have dark-grey skin with a yellowish stripe running form their mouth, down their necks. They have small, round, yellow eyes. If you’d like to tell the difference between males and females, the male has a much wider and longer tail than the female, and fully grown males are often larger than females.
They are a widely spread species, found in rivers throughout eastern Australia.
Unlike their aforementioned reptile relatives, the gender of Murray river turtles is not determined by heat during incubation but by the same means as human sex-determination, the X-Y sex-determination system. They are one of the few turtles with this system.
On average they grow to about 30cm in length. Compared to other freshwater Australian turtles, their necks are quite short, hence the name. They are omnivorous, with diets including water plants, algae, crustaceans and mollusks (like snails).
Of course, turtles do not only live in freshwater, there are seven species of saltwater turtles, six of which are found in Australian waters. Let’s look at one of them now.
Green Sea Turtle
You might look at these beautiful creatures and say… wait.. they’re not that green!
Well, the name actually comes from the colour of their fat tissue. This colour is a result of their diet, which consists mainly of sea grasses and algae. They are the only species of turtle that eat large amounts of these plants as adults.
Although the adults are Herbivores (Vegetarians), juveniles will also eat invertebrates, sponges and jellyfish.
Green Sea Turtles can live to over 50 years, grow to over 150cm in length and weigh over 300kg. Like the Murrary River Turtle, the males are typically larger than the females, with larger tails.
They mate every two to four years and when it comes time to lay their eggs, the females will climb out of the water, onto the land. This is usually a sandy beach and often the same beach where they hatched. They use their flippers to dig a hole in which to lay 100-200 eggs. They then fill the hole back in and return to the ocean.
After about two months the eggs hatch to face the most dangerous challenge of their lives, their first journey to the ocean. There are many predators who wait to feed on these little hatchlings as they attempt to make it to the water.
Like many of the reptiles we have spoken about, the gender of the hatchlings is determined by temperature during incubation. In warmer temperatures (around 31 degrees), most of the hatchlings will be female, while cooler temperatures (around 28 degrees) they will be mainly male.
Green Sea Turtles populations are wide spread around the planet and lay their eggs across the coastlines of over 80 countries. Australia is lucky enough to host one of the largest nesting populations.
Something really cool about them is that they use the magnetic field of the earth to navigate. Essentially there is a magnetic mineral in their brains called magnetite, which helps them navigate, like an internal GPS.
Unfortunately, they are classified as an endangered species. This is due to a number of reasons including being hunted for their meat, becoming caught in nets and downing and the destruction of their nesting sites. In fact, all seven species of sea turtle are threatened with extinction, being classified either as vulnerable, endangered or critically endangered.
A lot of my overseas friends refuse to visit Australia because of the snakes. But they’re really not as scary as everyone thinks. A lot of the fear surrounding these Aussie Animals comes from a lack of understanding.
There are over 3,000 species of snake in the world. Of that number, only 173 call Australia home.
Contrary to popular belief, most snakes are not naturally aggressive animals. They prefer to retreat than attack. And they will generally only attack humans when they are hurt or provoked.
Unfortunately, many snake populations are in decline, due to habitat destruction, (from bushfires and land clearing), introduced predators (such as foxes, dogs and cats), being run over by cars or simply being killed on sight by humans.
It is VERY unlikely that you will be bitten. Lightning strikes, dog attacks and peanut allergies attribute to more human deaths in Australia per year than snakebites.
I’m going to introduce you to a couple of our local snakes, so we can learn to understand them a bit better.
Eastern and Western Brown Snakes
These snakes can be found throughout much of mainland Australia. But if you’re staying in Tasmania you won’t spot any. As the name suggests, they are generally brown in colour. But this brown varies, from light to dark, even to orange-brown. The Eastern can grow to around 2m and the Western to around 1.8m.
Before we continue, lets define “Venom”. Do you know the difference between venomous and poisonous? Venom is a mixture of toxins which are delivered, usually through a bite or sting, from one organism to another. Essentially, it is a specialised form of poison that is actively delivered. The difference is, where other poisons may be eaten, or passed across skin, venom is delivered with a specialised evolutionary tool, for example the fangs of a snake or the stinger of a bee.
The Eastern Brown is typically very aggressive. Their fangs are actually quite small compared to other Australian Snakes. They are second on the list of most venomous terrestrial snakes (Terrestrial meaning they live on land). But don’t get too worried just yet, to put it in perspective, there were 19 human deaths caused by snakebites between 2005-2015 and 15 of those were caused by the Eastern Brown Snake. Generally only 1-4 deaths per year in Australia can be attributed to snake bites.
The Western Brown snake was once believed to be a single species but has since been recognised as a group of at least three, closely related species. They are less aggressive than their eastern counterparts and vary greatly in pattern and colour. They will typically flee from humans but will defend themselves if they believe they are under threat. Like the Eastern Brown, the Venom of a Western is very potent.
Even for those very few people, unlucky enough to be bitten, anti-venom is available. Brown snake anti-venom can be used for both species and has been available since 1956. Anti-venom acts to neutralise the effects of the venom. Not everyone who is bitten by a snake necessarily needs the anti-venom. However, a bite from any brown snake should be assumed as life threatening and should be treated as such. Seek medical attention immediately, call an ambulance!
Inland Taipan Snake
So, if the eastern brown snake holds the title of the second-most venomous terrestrial snake, what’s the first?
I’d like to introduce you to the Inland Taipan Snake, also known as the fierce snake. They’ve got quite the reputation! And fair enough as they’re the most venomous snake in the world! They grow to an average length of two metres, with the largest length recorded as 2.5 metres. Their colour changes with the seasons, darker in winter months and lighter in summer.
They were first discovered in 1879 and again spotted in 1882 before seeming to disappear for 90 years until their rediscovery in 1972.
Luckily, they have a fairly small distribution and are only found in south west Queensland and north east South Australia, around the border of the two states. They once had populations in NSW and Victoria but are now presumed to be extinct in these areas.
As they spend most of their time in cracks or burrows below the surface and because of the remoteness of their habitat, they are rarely seen by humans in the wild. They are generally a very placid and shy species but will defend themselves if they feel threatened.
One study found only 4% of snakebite patients were administered Taipan anti-venom. So again, your chances of running into one are quite slim!
Australia is home to two species of crocodile, the freshwater crocodile and the saltwater crocodile. (Although the freshwater croc is only found in Australia, the saltwater is also found in other countries, such as India, New Guinea and Malaysia).
Lets start with the Freshwater:
Males can grow up to 3 metres long, while females are considerably smaller, getting to a maximum of 2 metres. Their diet consists of smaller river animals such as turtles, fish, frogs and birds as well other animals that come to the water to drink. They do not eat people! So don’t worry. They generally only attack humans if provoked.
Just like the frilled-neck lizard (and many other reptiles), the gender of the young is determined by incubation temperature.
If you thought the freshwater crocs were big, you’ve got another thing coming. Saltwater males can grow up to 7 metres and females up to 4 metres! And they can weight up to 1000kg! They are the earth’s largest extant crocodile. Reminder: Extant meaning, not extinct. Due to their larger size, they are able to prey on larger animals and are known to eat cows and pigs when they come to drink at the water as well as wallabies and even other crocodiles!
No one is sure how long they live for but they have lived up to 50 years in captivity.
They are “opportunistic predators”, meaning that they wait patiently under water for their prey to come for a drink. They leap from the water, grasp their prey and drag it back into the water, keeping it under until it drowns. They will eat almost anything that they can catch.
They can stay submerged under water for over an hour.
Don’t worry too much, they’re only found in northern Australia. And even if you’re there, just make sure to be safe, follow the rules, don’t swim in any unfamiliar waters without knowing it’s safe first.
So how can we tell the difference?
Aside from the size, there are a couple of ways to distinguish between the two species.
Firstly, the shape of their teeth and heads. Saltwater crocodiles have broader snouts than the freshwater crocs, they also have uneven teeth (some teeth are twice the size of others) whereas the freshwater crocs have teeth that are almost equal in size.
That brings us to the end of the episode. I hope you’ve enjoyed getting to know some of our scaly Aussie wildlife. You probably won’t encounter most of them in the wild but I encourage you to head to the zoo and meet some of them in person!
Thanks for tuning in, until next time!