Wild Island

If you’ve ever heard a possum thumping around in your roof at night, chances are you weren’t thinking about the habitat value of your house. We tend to draw a fairly clear boundary between a home for people and habitat for wildlife.

New Australian research suggests that boundary is nowhere near as clear as we might think.

Researchers examining more than a decade of wildlife rescue records in Victoria have found native animals using many different parts of buildings to sleep, nest, roost and forage. Roof spaces, wall cavities, chimneys, balconies, sheds, roller doors and even heating and cooling systems were among the structures being used by dozens of native species.

The animals were also using different parts of buildings in ways that reflected their natural ecology. Species that normally seek hollows were using cavities, animals associated with trees were more likely to use higher parts of buildings, while ground-dwelling species were more commonly found underneath them.

Understanding what animals are finding in our buildings could also change the way we think about designing them, particularly as natural habitat continues to disappear or change around Australia’s towns and cities.

What Did the Study Actually Find?

The study was led by Bethany Kiss, an architect and researcher working across architecture and urban ecology, alongside researchers in conservation science, ecology and urban design. Using Wildlife Victoria’s rescue records from across Victoria between 2013 and 2022, the team began with a dataset of 76,663 wildlife reports.

Not every animal found inside a building was considered evidence of habitat use. That distinction was important. An animal flying through an open window or becoming trapped indoors might simply have been in the wrong place at the wrong time. The researchers were looking specifically for behaviours such as nesting, sleeping or roosting, and foraging, where the building itself appeared to be providing something the animal needed.

After automated screening and manual checking of thousands of records, the original dataset was reduced to 2,399 verified wildlife building interactions involving 36 native species and 27 different building features.

The most frequently recorded parts of buildings were:

Building Feature	Recorded Interactions
Interior roof spaces	544
Garages and sheds	280
Under houses	223
Roller doors	132
Wall cavities	132
Exterior roofs	116
Heating, ventilation and cooling systems	102
Balconies	95
General living spaces	84
Mailboxes or hanging baskets	75
Doors	75
Outdoor living areas	74
Chimneys	67
Windows	66

Roof spaces were the single most commonly recorded feature and were used by 26 different species.

Mammals dominated the records, particularly brushtail possums, ringtail possums, microbats and bare-nosed wombats. Birds and reptiles also appeared across a broad range of structures, including balconies, rooftops, chimneys, sheds and even heating and cooling systems.

Who’s Living Where?

Possums probably come as little surprise to anyone who has ever been woken by what sounds like a small furniture removal company operating in the ceiling. Common brushtail and common ringtail possums featured prominently in the records, particularly in roof spaces and other elevated cavities. Microbats were also frequent occupants, using roof and wall cavities as sheltered places to roost.

Closer to the ground, the residents changed. Bare-nosed wombats were strongly associated with spaces underneath houses, effectively finding shelter beneath the building rather than inside it. Blue tongues also turned up around heating, ventilation and cooling systems and other utility areas, while some were repeatedly recorded climbing onto and living on roofs.

Masked lapwings nested on exterior roofs, Pacific black ducks nested on balconies, and magpies were even recorded nesting in plumbing infrastructure.

Echidnas appeared beneath houses, tiger snakes were recorded sleeping in roof cavities and laughing kookaburras turned up in places including windows and shower exhaust fans.

A duck nesting on a balcony or a tiger snake sleeping above the ceiling might sound like an odd exception. Across the whole dataset, however, clear patterns emerged in which parts of buildings different animals were using.

A House Through an Animal’s Eyes

To understand why wildlife is using our buildings, it helps to stop looking at a house as a house.

To a possum, a dark enclosed roof space may offer some of the same qualities it seeks in a tree hollow. To a microbat, a narrow cavity inside a wall can provide a sheltered place to roost. Beneath a raised house, a wombat may find an enclosed space at ground level that provides some of the shelter it would normally seek underground.

The researchers found the same pattern across the dataset. Arboreal species were more strongly associated with elevated parts of buildings, while terrestrial species were more likely to use features closer to the ground. Animals that naturally depend on hollows and other enclosed shelters repeatedly appeared in roof spaces and wall cavities.

Parts of our buildings can provide some of the same things wildlife seeks in natural habitat. A cavity can offer shelter or somewhere to roost, while the height, position or temperature of a particular space may make it attractive to another species.

A roof cavity is not equivalent to an old hollow-bearing tree, and a house cannot replace the complexity of natural habitat. But to an animal searching for somewhere to sleep, nest or shelter, what may matter in that moment is not whether the structure is a tree or a building, but whether it provides the conditions it needs.

Understanding why animals recognise these opportunities becomes even more important when some of the natural features they depend upon are disappearing from the surrounding landscape.

When Natural Habitat Becomes Harder to Find

Tree hollows are a particularly important example. More than 300 Australian native animal species use hollows, yet suitable hollows can take up to 250 years to develop. When mature trees are removed through land clearing, development or the gradual loss of old trees in urban areas, that resource cannot simply be recreated by planting a young replacement tree.

The problem can persist even where cities retain substantial green space. A 2014 study of Canberra’s urban landscape predicted an 87 per cent decline in hollow-bearing trees over 300 years under existing management practices. Under its worst-case scenario, hollow-bearing trees could disappear from urban green space within 115 years. A landscape can remain green while steadily losing one of its most important habitat features.

That decline provides important context for the Wildlife Victoria research, but the two should not be confused. The study did not demonstrate that habitat loss directly caused each of the 2,399 recorded animals to move into a building. The rescue records tell researchers where wildlife was sleeping, nesting and foraging, but they cannot tell us whether a particular possum chose a roof because its former hollow had disappeared.

The study does show that buildings are already providing some of the functions wildlife normally finds in natural habitat. The authors argue that these accidental spaces may become increasingly important as urbanisation and habitat loss continue.

There are limits to that adaptability. The species appearing in buildings are the animals able to recognise and use the opportunities our architecture happens to provide. Many other species have highly specialised habitat requirements that a roof, wall cavity or shed could never reproduce. Wildlife using buildings should therefore not be mistaken for evidence that animals can simply adapt their way out of habitat loss.

And even for the species that can make use of our homes, finding something that looks like suitable habitat does not necessarily mean they have found somewhere safe. If possums are making themselves at home around your place, our How to Coexist With Possums guide looks at practical ways to live alongside them safely and reduce conflict without harming wildlife.

When Accidental Habitat Becomes a Trap

Finding somewhere that appears suitable is only part of the equation.

Natural tree hollows can buffer animals from temperature extremes, while cavities constructed from materials such as timber or steel may experience much greater fluctuations. A space that appears suitable to an animal may therefore provide very different conditions from the natural shelter it resembles.

Buildings also expose wildlife to hazards they would not encounter in a tree hollow. The researchers point to risks including electrical wiring, artificial lighting and pest control chemicals, all of which can affect animals using buildings as habitat.

The result can be what ecologists call an ecological trap. An animal responds to cues that would normally lead it towards suitable habitat, but those same cues draw it into an environment where its chances of survival or successful breeding may actually be lower. A dark enclosed cavity can still look like a good place to shelter even when something about the building makes it unsafe.

There is another complication in the Wildlife Victoria records themselves. These were rescue and wildlife assistance records, which means they are naturally more likely to capture situations where an animal had been noticed, was in trouble or had come into conflict with people. A possum quietly using a shed for ten years without bothering anyone is far less likely to generate a record than one trapped inside a wall.

That means the 2,399 interactions cannot tell us how common peaceful wildlife coexistence really is. If anything, there may be an entire layer of unreported coexistence occurring around us that rescue records don’t capture.

Nor does recognising buildings as habitat mean simply accepting wildlife inside every part of our homes. Sharing a roof cavity with a possum or discovering bats inside a wall can create genuine welfare, safety and practical problems for both people and animals. The more useful question is whether we can understand what wildlife is seeking in those spaces and provide it somewhere safer.

What If We Designed Buildings for Wildlife?

Animals are already finding habitat within buildings that were never designed with them in mind. Some researchers are now exploring what might happen if those opportunities were considered from the beginning.

This is the idea behind wildlife inclusive building design. Rather than treating biodiversity as something confined to parks, gardens and vegetation surrounding a development, it considers whether the buildings themselves can provide habitat too.

That could mean incorporating protected cavities for animals that naturally depend on hollows, creating nesting spaces within exterior walls, or designing roosting sites with the height, entrance size and temperature conditions required by particular species. Crucially, these spaces could be separated from the parts of a building occupied by people, providing wildlife with somewhere suitable without requiring a possum to discover its own entrance into the ceiling.

One version of this idea is already being used in Brighton and Hove in the United Kingdom, where new developments five metres or more in height are required to incorporate swift bricks or boxes. The council prefers swift bricks, small nesting cavities built directly into exterior walls, because they become a permanent part of the building and provide better temperature control than boxes attached to the outside. For smaller residential developments, at least three are required, or two for every dwelling, whichever is greater.

Brighton and Hove introduced the planning condition in 2020, partly in response to the loss of the small spaces in roofs and beneath eaves that swifts traditionally used for nesting. Modern construction and renovation had progressively taken many of those opportunities away.

Because swift bricks are incorporated into the exterior wall, they provide nesting space without giving birds access to the interior of the building. Other cavity nesting birds can use them too. The United Kingdom has also debated requiring swift bricks more widely, although no national requirement has been introduced.

The Australian research suggests this approach could extend well beyond nesting bricks. If possums seek elevated cavities, microbats use narrow protected spaces and some ground-dwelling animals shelter beneath buildings, architects and ecologists can begin identifying the characteristics those animals are selecting and whether safer versions could be incorporated deliberately.

Simply adding a few cavities to a building is not enough. Wildlife inclusive design needs to consider the ecology of individual species, the surrounding habitat and the potential for conflict with people. A nesting cavity is of little value if there is nowhere nearby to forage, while poorly designed artificial habitat could simply create another ecological trap.

Australian researchers have already developed Biodiversity Sensitive Urban Design, which brings biodiversity into the development process from the beginning rather than treating it as landscaping to be added afterwards. The new research brings the building itself into sharper focus. Walls, roofs, facades and other structures can become part of the ecological landscape too.

Bethany Kiss is already experimenting with a stranger version of the idea, using a building material specifically designed for wildlife to pull apart.

Architecture Wildlife Can Actually Use

Later this month, an installation called Peckable Architecture will appear at Melbourne’s Fed Square as part of Design X Nature. Created by Kiss with ecologists Jacinta Humphrey and Sarah Bekessy and designer Shane Hunt, the installation is designed not just to accommodate wildlife, but to be physically used by it.

The installation consists of biodegradable composite bricks packed with materials birds can use to build their nests. Bark, casuarina needles, fine twigs and moss are bound together with an organic gelatine binder, creating blocks that birds can peck apart and carry away piece by piece. Rather than trying to keep wildlife from damaging a building, the damage is quite literally part of the design. 

The idea has an ecological purpose beyond the novelty of birds dismantling a building. Suitable nesting materials can be scarce in heavily modified urban environments, where birds may instead collect artificial materials such as plastic debris and cigarette butts. Peckable Architecture makes the building itself a source of nesting material.

It is deliberately experimental. The bricks are designed to gradually disappear as birds remove their contents or the material naturally decomposes. The project describes this as planned obsolescence with an ecological purpose, creating architecture that is expected to change because another species has used it.

Peckable Architecture will be on display at Fed Square from 25 September to 18 October 2026. The research documenting how wildlife is already using our buildings is now feeding into experiments with buildings designed to respond to wildlife in return.

Making Room for Wildlife

Perhaps the most interesting thing these records reveal is not simply that wildlife is living in our buildings, but how readily some species can find opportunity in places we never intended to provide it.

That gives us another way to think about the places we have already built, and the enormous amount of development still to come. Houses, apartments and other structures will continue to occupy landscapes shared with wildlife. Designing them need not be solely about how effectively we can keep animals out. In some places, small parts of those buildings might safely give something back.

Making room for wildlife need not involve much space. A cavity incorporated into a wall, a protected roosting space or a nesting brick occupies only a tiny fraction of a building. Designed for the right species and supported by suitable habitat around it, that small architectural decision could remain in place for decades.

We have spent a long time drawing a fairly firm line between the places we build for ourselves and the places we consider wildlife habitat. The Wildlife Victoria records suggest that, for at least some of the animals living alongside us, that line is nowhere near as clear as we thought.

---

This article draws extensively from the 2026 study Buildings as accidental habitat: Where animals nest, sleep and forage, by Bethany M. Kiss and colleagues, published in People and Nature. The study analysed Wildlife Victoria rescue records from 2013 to 2022 to investigate how native wildlife uses buildings for nesting, sleeping, roosting and foraging.

---

Editorial Note: Wild Island is committed to publishing accurate, evidence based wildlife information. This article has been researched using authoritative sources, including government agencies, scientific institutions and peer reviewed literature. The information in this article was verified at the time of publication and will be updated if significant new evidence or guidance becomes available.

Cover Image by Andrew Mercer / CC BY-SA 4.0