Artificial refuges are a popular stopgap for habitat destruction, but the science isn’t up to scratch


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Darcy Watchorn, Deakin University; Dale Nimmo, Charles Sturt University; Mitchell Cowan, Charles Sturt University, and Tim Doherty, University of SydneyWildlife worldwide is facing a housing crisis. When land is cleared for agriculture, mining, and urbanisation, habitats and natural refuges go with it, such as tree hollows, rock piles and large logs.

The ideal solution is to tackle the threats that cause habitat loss. But some refuges take hundreds of years to recover once destroyed, and some may never recover without help. Tree hollows, for example, can take 180 years to develop.

As a result, conservationists have increasingly looked to human-made solutions as a stopgap. That’s where artificial refuges come in.

If the goal of artificial refuges is to replace lost or degraded habitat, then it is important we have a good understanding of how well they perform. Our new research reviewed artificial refuges worldwide — and we found the science underpinning them is often not up to scratch.

What are artificial refuges?

Artificial refuges provide wildlife places to shelter, breed, hibernate, or nest, helping them survive in disturbed environments, whether degraded forests, deserts or urban and agricultural landscapes.

Nest boxes are a commonly used artificial refuge for tree-dwelling animals.
Ed Reinsel/Shutterstock

You’re probably already familiar with some. Nest boxes for birds and mammals are one example found in many urban and rural areas. They provide a substitute for tree hollows when land is cleared.

Other examples include artificial stone cavities used in Norway to provide places for newts to hibernate in urban and agricultural environments, and artificial bark used in the USA to allow bats to roost in the absence of trees. And in France, artificial burrows provide refuge for lizards in lieu of their favoured rabbit burrows.

An artificial burrow created for a burrowing owl.
AZ Outdoor Photography/Shutterstock

But do we know if they work?

Artificial refuges can be highly effective. In central Europe, for example, nest boxes allowed isolated populations of a colourful bird, the hoopoe, to reconnect — boosting the local genetic diversity.

Still, they are far from a sure thing, having at times fallen short of their promise to provide suitable homes for wildlife.




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One study from Catalonia found 42 soprano pipistrelles (a type of bat) had died from dehydration within wooden bat boxes, due to a lack of ventilation and high sun exposure.

Another study from Australia found artificial burrows for the endangered pygmy blue tongue lizard had a design flaw that forced lizards to enter backwards. This increased their risk of predation from snakes and birds.

And the video below from Czech conservation project Birds Online shows a pine marten (a forest-dwelling mammal) and tree sparrow infiltrating next boxes to steal the eggs of Tengmalm’s owls and common starlings.

The effects of predation should be considered when using artificial refuges.

So why is this happening?

Our research investigated the state of the science regarding artificial refuges worldwide.

We looked at more than 220 studies, and we found they often lacked the rigour to justify their widespread use as a conservation tool. Important factors were often overlooked, such as how temperatures inside artifical refuges compare to natural refuges, and the local abundance of food or predators.

Alarmingly, just under 40% of studies compared artificial refuges to a control, making it impossible to determine the impacts artificial refuges have on the target species, positive or negative.

This is a big problem, because artificial refuges are increasingly incorporated into programs that seek to “offset” habitat destruction. Offsetting involves protecting or creating habitat to compensate for ecological harm caused by land clearing from, for instance, mining or urbanisation.

For example, one project in Australia relied heavily on nest boxes to offset the loss of old, hollow-bearing trees.

But a scientific review of the project showed it to be a failure, due to low rates of uptake by target species (such as the superb parrot) and the rapid deterioration of the nest boxes from falling trees.




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The future of artificial refuges

There is little doubt artificial refuges will continue to play a role in confronting Earth’s biodiversity crisis, but their limitations need to be recognised, and the science underpinning them must improve. Our new review points out areas of improvement that spans design, implementation, and monitoring, so take a look if you’re involved in these sorts of projects.

We also urge for more partnerships between ecologists, engineers, designers and the broader community. This is because interdisciplinary collaboration brings together different ways of thinking and helps to shed new light on complex problems.

Some key steps arising from our research which suggest a way forward for artificial refuge science and implementation.
Author provided

It’s clear improving the science around artificial refuges is well worth the investment, as they can give struggling wildlife worldwide a fighting chance against further habitat destruction and climate change.




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The Conversation


Darcy Watchorn, PhD Candidate, Deakin University; Dale Nimmo, Associate Professor in Ecology, Charles Sturt University; Mitchell Cowan, PhD Candidate, Charles Sturt University, and Tim Doherty, ARC DECRA Fellow, University of Sydney

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

DIY habitat: my photos show chainsaw-carved tree hollows make perfect new homes for this mysterious marsupial


William Terry, Author provided

William Terry, Southern Cross UniversityEnvironmental scientists see flora, fauna and phenomena the rest of us rarely do. In this series, we’ve invited them to share their unique photos from the field.


As a result of logging and severe bushfires, Australian wildlife is facing a severe shortage of tree hollows — holes in the trunks and branches of large old trees. More than 300 species of birds and mammals, including possums, bats, cockatoos, owls and kookaburras, rely on tree hollows for shelter or breeding.

A sacred kingfisher using a natural tree hollow for nesting.
William Terry

In Australia, hollows are usually formed through the decay of a tree scar, and it can take hundreds of years for tree hollows big enough for medium-sized animals to form naturally.

This includes phascogales — the rat-sized, carnivorous marsupials that live in open woodlands across Australia and are the focus of my research and photography. But like many of Australia’s forest-dwelling mammals, phascogales are vulnerable to extinction.

So with hollows becoming harder to find, I venture into forests and study how well artificial hollows, made with chainsaws, can replace them. And, incredibly, it’s working: my research shows phascogales and other native animals are enthusiastically moving into the new real estate.

Meet the mysterious brush-tailed phascogale

Phascogales are an important species to Australia but, unfortunately, their cryptic behaviour and nocturnal habits mean people rarely see them.

Brush-tailed phascogales live in trees, but will come to the ground to forage for food among leaf litter and fallen timber.
William Terry
Phascogales belong to the same family as the Tasmanian devil, quoll (pictured) and the tiny antechinus.
William Terry, Author provided

Phascogales feed on insects after stripping bark from eucalypts. But through my close interactions and radio tracking, I’ve documented phascogales eating other more unusual foods, including bird eggs and sometimes even small birds, such as grey-shrike thrush.

I’ve also recorded them taking dead birds, such as the rosella pictured below. They even have a reputation among farmers as being a fierce chicken killer, but this may be exaggerated.

A phascogale inspects a dead crimson rosella it found at the base of a tree. Moments later, this phascogale dragged the bird away. It was unclear what happened next.
William Terry

Phascogales have an unusual life. Shortly after mating between April and May, all males die at about 11 months of age from stomach ulcers. This frees up resources for the next generation of young joeys that will emerge from the nest in early summer.

But will they survive in the future?

Tragically, at least one species, the brush-tailed phascogale, is threatened with extinction, primarily due to habitat loss, climate change, and feral predators such as foxes and cats.

The brush-tailed phascogale (Phascogale tapoatafa tapoatafa) occurs across the eastern side of Australia, from southern Queensland to Victoria. It’s now extinct in South Australia.

Likewise, the much smaller red-tailed phascogale (Phascogale calura) once survived across a vast swathe of land from Western Australia to Victoria. Today, it survives only in small pockets in the Western Australia wheatbelt.

Brush-tailed phascogales were once known as ‘bottle-brush squirrels’, due to the stunning resemblance of its tail to the iconic native flowers.
William Terry
The red-tailed phascogale has been lost from much of its former range and now only exists in the Western Australian wheatbelt.
William Terry, Author provided

Household cats are a particularly major issue for phascogales, and many cat owners in central Victoria have a story about their cat bringing home a phascogale (so please keep your pet cat inside at all times).




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Last year, research confirmed climate change would reduce the available areas phascogales could survive. This research found areas with a phascogale-friendly climate would decline by up to 79% in Queensland, 67% in Victoria and 17% in NSW, by 2070.

Climate change also threatens to bring longer, more frequent and severe heatwaves. For phascogales and many other mammals, this could be a death sentence.

Tree hollows with thick walls can protect the animals sheltering inside from the high temperatures outside.

But these are getting increasingly rarer, and this is where my research on chainsaw hollows comes in. Thick-walled hollows may be very important for the long-term survival of phascogales and other species in a warming climate.

A relative to the phascogale, the tiny agile antechinus commonly uses tree hollows on the ground.
William Terry, Author provided

Carving them a home

A chainsaw hollow is a cavity constructed inside a tree. A faceplate is then attached over the top, with a hole drilled into it for the animal to enter. They offer refuge for Australia’s endangered mammals and birds.

For our project, we carved 45 chainsaw hollows in dry forests and woodland where phascogales are known to occur. We also installed similar-sized nest boxes — which are more commonly used to offset the loss of hollows — on nearby trees. We monitored these for two and a half years.

A chainsaw hollow constructed for phascogales.
William Terry, Author provided
Chainsaw hollow creation is a specialised skill. Here, tree climber Lachlan installs a chainsaw hollow on a red ironbark tree.
William Terry, Author provided

Research from 2018 shows nest boxes offer little protection from outside temperatures. I’ve collected data, which is not yet published, that confirms this.

My research shows chainsaw hollows provide 27% more protection from extreme temperatures during heatwaves compared to nest boxes, which provided almost no protection.




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Two phascogales peeking out of a nest box.
William Terry, Author provided

So it’s no wonder we observed and recorded phascogales and the more common sugar glider (Petaurus notatus) more frequently sheltering in chainsaw hollows than in nearby nest boxes.

Other animals used the chainsaw hollows, too. This includes the feather-tailed glider, yellow-footed antechinus, and the white-throated treecreeper.

Brush-tailed phascogale inspects a chainsaw hollow.
Sugar gliders also frequently used chainsaw hollows.
William Terry

But like nest boxes, the chainsaw hollows showed signs they would be only an interim measure, requiring maintenance with bark growing over entrance holes and issues with a buildup of moisture.

In any case, further research into this species is needed, as it will aid land managers to conserve this enigmatic species as more challenges are thrown their way into the future.




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William Terry, PhD Researcher, Supervision by Associate Prof. Ross Goldingay, Southern Cross University

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