Author Archives: The Conversation

Torpor: a neat survival trick once thought rare in Australian animals is actually widespread

echidna-torpor-shutterstock

LIFE IS HARD for small animals in the wild, but they have many solutions to the challenges of their environment. One of the most fascinating of these strategies is torpor. Not, to be confused with sleep or Sunday afternoon lethargy, torpor is a complex response to the costs of living.

To enter torpor, an animal decreases its metabolism, reducing its energy requirements. A torpid animal will often be curled in a tight ball in its nest and look like it’s sleeping.

Once thought to occur only in birds and mammals in the Northern Hemisphere where winters are more pronounced, we now know torpor is widespread in small Australian mammals, and has also been observed in many small Australian bird species.

ABOVE: Echidnas use torpor to save energy. (Shutterstock)

Read more:
Animal response to a bushfire is astounding. These are the tricks they use to survive


Masters of metabolism

Birds and mammals are endotherms and can maintain a high and constant body temperature independent of the environmental temperature, thanks to their high metabolic rate. This allows them to be active across a wide range of environments.

The downside? This high metabolic rate requires a lot of food to fuel it. By reducing the metabolism in a very controlled manner and entering torpor, an animal can live on less energy.

With a lower metabolic rate, the animal’s body temperature decreases — sometimes by as much as 30°C. How low it goes can depend on the extent of the metabolic reduction and the temperature of animal’s immediate environment. The reduced body temperature further lowers the metabolic rate.

Slowing down to survive

Torpor is an extremely effective survival strategy for small endotherms. For example, small mammals have been observed using torpor after bushfires.

Take the brown antechinus, for example. When other animals have fled, this 30g marsupial hides in refuges, waits out the fire, then uses torpor to cope with reduced food availability until local vegetation and invertebrate populations recover.

A brown antechinus on a tree.
The brown antechinus uses torpor to cope with reduced food availability after bushfire. (Shutterstock)

Many pregnant and lactating bats and marsupials, and even the echidna, synchronise torpor with reproduction to cope with the energetic costs of mating, pregnancy or lactation.

There are two main types of torpor: daily torpor and hibernation.

Daily torpor

Animals that use daily torpor can do so for approximately 3–6 hours a day as needed.

Daily torpor is common in, but not exclusive to, endotherms living in arid areas, such as the fat-tailed dunnart. This species is a carnivorous marsupial and has a diet of insects and other invertebrates, which may be in short supply in winter.

A fat-tailed dunnart.
When finding enough food is difficult, the fat-tailed dunnart uses torpor. (Shutterstock)

Weighing approximately 12 grams as adults, the fat-tailed dunnart may need to eat its body weight in food each day. When finding enough food is difficult, it uses torpor; foraging in the early part of the night then entering torpor in the early morning. Fat-tailed dunnarts reduce their metabolic rate, and subsequently their body temperature, from 35°C to approximately 15°C, or the temperature of their underground nest.

Hibernation

Animals that hibernate lower their metabolic rate further and have longer torpor bouts than those that use daily torpor. An example of an Australian hibernator is the eastern pygmy possum, a 40g marsupial found in south eastern Australia that hibernates regularly, decreasing its body temperature from approximately 35°C to as low as 5°C.

When active, this species can survive for less than half a day on 1g of fat, but when hibernating, it can survive for two weeks.

A torpid eastern pygmy possum. Note the curled posture.
Photo credit: Chris Wacker, Author provided

If it weren’t for the periodic increases in metabolic rate and body temperature, a hibernating pygmy possum could live for well over three months on 1g of fat. However, the exact purpose of these periodic arousals is unknown.

The metabolic rate during pygmy possum hibernation is just 2% of the minimum metabolic rate endotherms at a normal body temperature need to live. This baseline metabolism is called basal metabolic rate.

An American black bear
Black bears can’t hibernate with a lower body temperature. (Shutterstock)

Compare this with a well-known hibernator, the American black bear.

At approximately 120kg, its metabolic rate during hibernation decreases to 25% of the basal metabolic rate, and the body temperature decreases from approximately 37°C to 30 °C. Black bears can’t hibernate with a lower body temperature, perhaps because it would take them a very long time to reduce it, and then cost them too much energy to rewarm at the end of hibernation.

Can humans do it?

The question people often ask about torpor, is “can humans do it?” Interestingly, some small primates have been observed using torpor. While it is technically possible to induce torpor in humans chemically, torpor is a very complex physiological process, and there are many aspects of it scientists still don’t fully understand.

A gray mouse lemur in Madagascar.
The grey mouse lemur in Madagascar is among the primates that uses torpor. (Shutterstock)

Coping with climate change

Australia’s wildlife have evolved strategies to cope with life in an often-harsh environment affected by multiple year-long droughts, landscape-altering floods, and widespread bushfires.

Climate change is predicted to increase the duration, frequency and severity of these events, and in conjunction with landscape clearing, animals are facing new environmental and resource challenges.

While animals that use flexible, daily torpor may be well-suited to cope during these times, at least in the short term, hibernators that depend on long winters are most at risk.


Read more:
Summer bushfires: how are the plant and animal survivors 6 months on? We mapped their recovery


— Chris Wacker, Postdoctoral Research Fellow — School of Environmental and Rural Science, University of New England

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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UPDATE (Petition + Rally Weds 12 Aug). Our laws failed these endangered flying-foxes at every turn. (Qld)

spectacled-flying-fox-InigoMerriman_Conversation_July2020

Cairns council, Qld, will put another nail in the coffin.

CAIRNS REGIONAL COUNCIL will disperse up to 8,000 endangered spectacled flying-foxes from their nationally important camp in central Cairns.


NEWS UPDATES: 

• Sign petition by Tues 11 August (to reach 50,000 signature)
• Rally at Cairns Regional Council, 9am Weds 12 Aug (live-streamed)
> MORE INFO HERE

—————————————————————————-

PERIOD FOR THE DISPERSAL EVICTION HAS BEEN
EXTENDED FOR ANOTHER TWO MONTHS!
 
Continue reading >

The camp is one of the last major strongholds of the species, harbouring, on average, 12% of Australia’s remaining spectacled flying-foxes. But after recent catastrophic declines in spectacled flying-fox numbers, moving them from their home further threatens the species survival.

CAPTION: Spectacled flying-foxes are important pollinators and seed dispersers in Australia’s Wet Tropics. IMAGE: Inigo Merriman. [Yes the picture is placed the correct way.]


Read more:
Not in my backyard? How to live alongside flying-foxes in urban Australia


Yet, the federal environment minister approved the dispersal last month under the Environment Protection and Biodiversity Conservation Act (EPBC Act) — Australia’s key environment legislation for protecting threatened species, and currently under a ten-year review.

This planned dispersal — which the council says is in the interests of the species — is set to conclude a long series of controversial management actions at the site. The EPBC Act failed to protect the species at every turn. The camp may now be non-viable for the flying-foxes.

IMAGE: David Pinson, CC BY-NC-ND

Decline of the rainforest specialist

Spectacled flying-foxes are critical for pollination and dispersing fruit in Australia’s Wet Tropics, and so underpin the natural values of this world heritage-listed region.

But habitat destruction and harassment largely caused the species’ population to drop from 250,000 in 2004 to 75,000 in 2017. Subsequent monitoring has, so far, shown no sign of recovery.

In late November 2018, another 23,000 bats — a third of the population — died from heat stress. It marks the second largest flying-fox die-off in recorded history.

Today, the camp is not only home to a big portion of the species, but also around 2,000 pups each year. Flying-foxes are extremely mobile in the region, so the camp provides a roosting habitat for more than what’s present at any one time.

Endangered spectacled flying-foxes are set to be dispersed from their camp in Cairns CBD, one of the last strongholds of the species.
IMAGE: Justin Welbergen

Why dispersals don’t work

The council is permitted to disperse the flying-foxes with deterrent measures, including pyrotechnics, intense lighting, acoustic devices and other non-lethal means.

The Conversation sought a response to this article from Cairns Regional Council. A spokesperson said:

Relocation measures will only occur between May and September — outside of the spectacled flying fox pup rearing season to avoid a disruption to the species’ breeding cycle.

The relocation activity will be undertaken by appropriately qualified and experienced individuals and non-lethal methods will be used.

The program is tailored to minimise any stress on the animals and causes no injury of any type.

However, ample evidence shows dispersals are extremely costly, ineffective and can exacerbate the very wildlife management issues they aim to resolve.

Dispersals risk stressing the already disturbed animals, and causing injuries and even abortions and other fatalities. They also risk shifting the issues to other parts of our human communities, as the bats tend to end up settling in an unanticipated location after having been shuffled around town like a game of musical chairs.

Even in the often-cited example of the “successful” relocation of vulnerable grey-headed flying-foxes from the Melbourne Botanic Gardens in 2003, experts couldn’t direct the bats to their designated new camp.

Instead, the flying-foxes formed a permanent camp at Yarra Bend, one kilometre short of the intended destination, where they’re now subjected to renewed calls for culling or dispersal.


Read more:
No, Aussie bats won’t give you COVID-19. We rely on them more than you think.


‘Fogging’ is one of several methods used to disperse flying-foxes from their camps.  SOURCE: Australasian Bat Society

Poor management

Cairns Regional Council argues their decision to attempt to move the bats to the Cairns Central Swamp is in the long-term interest of their survival. A council spokesperson says:

Heat stress events, urban development and increased construction in close proximity to the Cairns City Library roost will continue to stress and adversely affect the spectacled flying fox population.

Also, the health of roost trees at the library site, and therefore the viability of the site as a spectacled flying fox roost, is diminishing. Council believes relocation will mitigate human/flying fox conflict, enable the trees at the library to recover, and will likely reduce the high rates of pup mortality that have been recorded at the library colony.

But these animal welfare concerns arose from the accumulated impacts of the council’s poor management actions, or actions the council supported.

In 2014, the council was found guilty, under the Queensland Nature Conservation Act, of driving away spectacled flying-foxes and illegally pruning the habitat trees.

Over the past seven years, most roosting trees of the Cairns CBD camp were either removed or heavily pruned, resulting in the destruction of more than two-thirds of the available roosting habitat.
IMAGE: Provided by authors.

The Cairns camp was then subjected to a series of EPBC-approved roost tree removals in 2014, 2015, 2016 and 2017. Collectively these destroyed more than two-thirds of the available roosting habitat at the site.

This directly contradicts the specific EPBC Act referral guideline, which states actions to manage the flying-fox camps should not significantly impact the species.

And in 2015, Cairns Aquarium developers had to destroy trees home to hundreds of spectacled flying-foxes before they could start construction. That’s because under the EPBC Act, no building near or around the flying-foxes is permitted. In this case, the act’s well-intentioned protection measures caused far more harm than good.

Removals (X) of roost trees from the Cairns flying-fox camp between 2013 and 2020. The new white rectangular buildings visible in 2020 are high-rise hotel (centre) and Cairns aquarium (top) developments.
IMAGE: Provided by authors.

Warnings fall on deaf ears

In the meantime, the national conservation status of the spectacled flying-fox moved too slowly from “vulnerable” to “endangered” in the listing process.

In 2017 the government’s own Threatened Species Scientific Committee advised listing the species as endangered, which would provide them with more protection.

But when the spectacled flying-fox was finally declared endangered in February 2019, they already qualified as critically endangered, according to official guidelines.


Read more:
Let there be no doubt: blame for our failing environment laws lies squarely at the feet of government


What’s more, the state government’s recovery plan for the spectacled flying-fox — in place since 2010 — has never been implemented.

Are there any solutions?

There are no solutions under the EPBC Act as it’s currently framed.

The tragic end to the story is that a dangerous precedent is being set for flying-fox management in Australia. Bat carers in Cairns are readying themselves for an influx of casualties from the dispersal.

Some bat carers have sadly reached the conclusion the dispersal is now the least-bad option for the bats after their stronghold suffered a death by a thousand cuts, leaving their home unviable.

The review of the EPBC Act must see strengthened legislation to prevent such tragic outcomes for our threatened species. Australia’s inadequate protections allow species to be pushed towards extinction at one of the highest rates in the world.


Maree Kerr contributed to this article. She is a co-convenor of the Australasian Bat Society’s Flying-Fox Expert Group; an invited expert on the Cairns Regional Council’s Flying-fox Advisory Committee; President of Bats and Trees Society of Cairns; and is studying the role of education in public perceptions of flying-foxes at Griffith University

Evan Quartermain contributed to this article. He is Head of Programs at Humane Society International and a member of the IUCN World Commission on Protected Areas.The Conversation

Justin A. Welbergen, President of the Australasian Bat Society | Associate Professor of Animal Ecology, Western Sydney University; Noel D Preece, Adjunct Asssociate Professor, James Cook University, and Penny van Oosterzee, Adjunct Associate Professor James Cook University and University Fellow Charles Darwin University, James Cook University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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