Australia's animals beat the summer heat using mucous, saliva and precision engineering
Summer in the sunburnt country can be a brutal cauldron of heat and humidity — and not just for its human inhabitants.
Unlike us, a lot of Australia's animals cannot sweat to keep cool.
But after thousands of years of evolution — if not millions — they've developed other creative thermoregulation solutions.
Whether it's going to sleep for a year, fly-by belly dipping or covering themselves in mucous, these are some of the fascinating and bizarre methods of fauna battling hot weather.
Kangaroo species can sweat but, strangely enough, only while hopping.
The rest of the time, if it gets hot, they have to find other ways to deal with high temperatures.
Eastern grey kangaroos (Macropus giganteus) mostly rely on panting, quick short breaths, for evaporative heat loss.
Red kangaroos (Macropus rufus), on the other hand, have much more reflective fur than other kangaroo species, giving it an advantage in desert habitats.
All kangaroos also like to give their forearms, which contain a whole heap of blood vessels, a lick.
As the moisture evaporates on their arms, they lose heat.
Shade can reduce exposure to solar radiation for big animals such as red kangaroos by 80 per cent.
Bioclimatic modelling has predicted that Northern Australia could see a dramatic halving in distribution areas for four kangaroo species — red kangaroo, eastern grey, antilopine (Macropus antilopinus) and common wallaroo (Macropus robustus) — if average temperatures exceed 2 degrees Celsius above pre-industrial levels.
The world is currently on track for about 3C of warming, according to the United Nations Environment Programme's latest emissions gap report from November.
Australia's unofficial national bird doesn't mind a dip in the ocean or watering holes when the mercury rises.
Generally emus (Dromaius novaehollandiae) remain active in hot parts of the day, unlike kangaroos.
To be able to stay out in the sun all hours, the emu relies on its coat of feathers.
Specifically, the two-toned colouring of each feather.
Black tips absorb heat radiating from the sun.
The bulk of greyish brown feathers underneath then helps prevent heat transfer to the emu's skin.
Wind can then blow the heat away.
An emu's walking speed generates the breeze needed to dispatch any heat build-up in the feathers.
They may look like tombstones or eerie monoliths, but the magnetic termite mounds of the Northern Territory are more akin to a well-orientated building.
The mounds reach about 2 metres in height and are made from clay, sand and some good old-fashioned (termite) spit.
As if drawn up by mini architects, the mounds have a general north-south orientation with the wider faces pointing east-west.
Facing north gave the mounds their "magnetic" moniker, but this orientation exploits wind direction and the Sun's movements to keep the structures' interior cool.
The broad faces catch maximum sun rays in the morning, but minimise this heat capture in the warmer parts of the day when the Sun is overhead.
With their usual aspect, the mounds maintain a temperature of between about 25 and 36 degrees C.
But a study from the 1970s found if you cut a mound and rotated it 90 degrees then the average temperature inside would be 7C warmer.
Termites elsewhere also engineer their mounds to best suit their local conditions.
A 2020 study created a computer model, based on existing observations, that could successfully predict the shape and orientation of a termite mound based on locational environmental conditions.
Because they also cannot sweat to stay cool, greater bilbies (Macrotis lagotis) have removed the problem of high daytime temperatures by avoiding them altogether.
Other than the noble greyhound, there is probably no other animal quintessential Australian father Darryl Kerrigan would be more proud of than the bilby.
And that's because the nocturnal bilby is a prolific digger of holes to provide refuge from the heat of the arid regions it is found.
Not just any holes either; these are spiralling burrows which can be 2 metres deep and 3 metres in length.
But the marsupial is not satisfied with just one holey home as its castle. The bilby keeps a network of about 12 burrows, and males have a home range upwards of 3 square kilometres.
It has been theorised, but not proved, the size of a bilby's ginormous rabbit-like ears also help expel heat from its body.
Since the bilby can only be in one burrow at a time, the rest can be used to shelter other critters thanks to the consistent temperature and humidity levels inside.
Brush-tailed mulgara and spinifex hopping mice have been recorded using bilby burrows as a permanent home, while echidnas and goannas can also shelter in them.
Research in the West Kimberley recorded 45 different types of animals — including birds, reptiles and mammals — entering or checking out bilby burrows.
Sometimes just digging a hole isn't enough to keep cool for species like the green-striped burrowing frog (Cyclorana alboguttata).
To avoid croaking (the death kind) during the dry spells of its east coast home, the amphibian just stops moving altogether for months on end until a big rain.
After digging backwards into the ground, the frog forms a cocoon of mucous and shed skin as it goes into a dormant state known as aestivation.
Aestivation is kind of like the seasonal opposite to a bear's hibernation when they go into a metabolic slowdown over cold northern hemisphere winters due to a lack of food.
Instead, a lack of water and high temperatures drives aestivation for frogs in Australia.
Without the cocoon, the frog would lose a critical amount of water in about 25 days and could die.
Amazingly, despite dormancy lasting up to about nine months on average, but sometimes over a year, the frog shows minimal signs of atrophy in its limbs.
Research suggests this is due to genes that prevent muscle wastage.
Sweating, licking and panting are all off the evolutionary cooling checklist for the short-beaked echidna (Tachyglossus aculeatus), but mucous is still in very much in play.
And unlike underground frogs, it doesn't need to cover its entire body in mucous to avoid the heat.
Instead snot production goes into overdrive, with the echidna's sleek snoot forming bubbles which provide a unique cooling mechanism.
Curtin University vertebrate ecophysiologist Christine Cooper told ABC RN's The Science Show that the bubbles wet an echidna's schnoz skin, under which lies a big blood sinus.
"So that wets that area, [and] as the water evaporates, it … cools the blood," Dr Cooper said.
The moisture also aids the echidna ability to detect weak electrical waves from prey, known as electroreception, with its snout.
"So they always tend to have a moist nose, but they can use that as well to keep cool, and they seem to make it more moist when they're hot," Dr Cooper said.
A wet proboscis is not the only way of shedding heat for the echidna.
While its back of spines helps echidnas to stay warm, their exposed bellies can be flopped onto a cool surface to transfer heat.
Koalas (Phascolarctos cinereus), the original Australian tree-huggers, love the high life and spend up to 20 hours asleep.
They eat about half a kilogram of leaves every day up in the tree tops, which is also how they get most of their water intake.
University of Melbourne research fellow Natalie Briscoe was looking into how koalas responded to high temperatures when she found something peculiar.
The koalas would move into the shade but Dr Briscoe said another strange pattern emerged.
"They were using a tree species they don't feed on … [hugging] the main trunks of trees and lower to the ground," she said.
"We came up with the idea they were losing heat to the tree trunks. I found a colleague with a fancy thermal camera and went out in hot weather and it's exactly what they were doing."
By pressing their body into the coolest tree they could find, the koalas halved their need to drink water in heatwaves.
Hugging trees may not be enough for koalas to maintain their already dwindling distribution with rising average temperatures.
Dr Briscoe, who is working on models for predicting species' response to climate change, said under global warming predictions, koala populations would contract towards the coast over the next 50 years.
Australia's flying fox species take body cooling to another level with a high-speed manoeuvre known as belly dipping.
The aerially inclined mammal will fly down low and drop its stomach into a water body, like a river, to wet its fur which it then licks off upon roosting.
The behaviour is generally displayed when they return home after foraging but also happens when in the middle of the day in hot weather.
Flying foxes also have a bunch of other cooling methods when they start to warm up.
First they will fan their wings to waft air over their body, then they'll seek out more shade before going further down a tree to get under more vegetation.
Flying foxes will also start hugging trees but, if they continue to heat up, will lick themselves like kangaroos and pant heavily.
Eventually they become lethargic and lie on the ground.
When temperatures get over 42C, flying foxes are at high risk of mass die-offs.
More than 200,000 flying foxes have died in such events since 2010.
About 23,000 spectacled flying foxes, representing a third of the Australian population of the species, died in 2018 from extreme heat.
A heat forecast tool has been developed to keep authorities and wildcare groups in the loop around potential "mortality events".
Western Sydney University animal ecologist Justin Welbergen said the issue was even broader than flying foxes, which scientists think could be an "indicator species".
"We suspect, and it is of concern, that flying foxes are kind of like bioindicators of the impacts of extreme heat events on other wildlife, wildlife with more cryptic lifestyles," he said.
"Flying foxes are not particularly special when it comes to extreme heat events. The only way they are different is they have this gregarious nature in the day. They roost in colonies, thousands of individuals."
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Researchers are looking into how climate change will affect flying foxes, as well as mitigation strategies.
Professor Welbergen said potential mitigation approaches included the lengthy process of creating more favourable vegetation, and in the short-term, use of misters and sprinklers.
"All those latter approaches with water, we have concerns about it," he said.
Professor Welberger said things like licking wings and panting were less effective in high humidity.
"By deploying water or sprinklers or misters we're artificially increasing humidity but we're also reducing temperature," he said.
"We don't know how those two forces balance out."
We acknowledge Aboriginal and Torres Strait Islander peoples as the First Australians and Traditional Custodians of the lands where we live, learn, and work.
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