A species · Mammal
Common brushtail possum
The thump and scrabble overhead at dusk, the harsh rasping growl from the fig tree — a hollow-denning marsupial generalist that simply moved into the roof cavity when the woodland came down, and is now most of the 'nature' an Adelaide child ever meets.
- On the gradient
- Not fixed to one rung — from the wetter gullies of the ranges to the flattest suburban street, wherever there is a den site and a garden to raid
- Rock
- Not tied to any one landform — dens wherever there is a cavity, from range-front stringybark to suburban terracotta
- Soil
- Not soil-bound — an arboreal generalist at home on garden loam and reworked plains alluvium alike
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What you'll take away
- Identify the common brushtail possum by its unmistakable urban signs — the thump and scrabble overhead at dusk, the harsh rasping cough, chewed rose buds and stripped fruit — as the sound of one of the region's few thriving native mammals.
- Explain why a dietary and den-site generalist marsupial could substitute roof cavities and garden plantings for the cleared woodland it evolved in, while more specialised natives could not.
- Use the possum, alongside the rosella, as a live case of the shifting baseline: an everyday sighting that quietly stands in for a richer mammal fauna most residents never knew existed.
- Contrast the possum's persistence with the region's mammal losses — the vanished bilby, the declining bandicoot — and read what that contrast says about which animals survive clearing and which do not.
Sooner or later, almost every Adelaide household has the same nocturnal argument with the roof: a thump, a scrabble, a pause, and then a long, guttural, rasping cough from somewhere above the ceiling that sounds far too large and far too displeased to belong to a marsupial the size of a cat.
That is the common brushtail possum announcing itself, and it is, whether the homeowner appreciates it or not, one of the better native-wildlife stories this cleared and citified region has to tell.
Brushtails are built for exactly the double life that lets them thrive here: strong, bare-skinned hind feet and a naked-tipped, prehensile tail for gripping branches — or a corrugated-iron roofline just as readily — and a stomach happy to work through leaves, blossom, fruit, buds, and, given the chance, whatever is coming into flower in next door’s vegetable patch.
None of that flexibility is an accident of the suburbs; it is the same trick that let the animal keep going through two centuries in which the woodland it evolved in was cut down around it.
A brushtail’s ancestral den is a hollow limb in an old eucalypt, the kind of cavity that takes a tree the better part of a century to grow — but a possum does not much care whether the dark, enclosed space it climbs into by day is a hollow a tree grew or a roof cavity a carpenter built, and so, as the old hollow-bearing trees came down across the Adelaide Plains, the possum moved into the replacement (Bradshaw 2012).
Very few of the region’s other native mammals had that option.
The greater bilby, the bandicoots, the bettongs and their relatives needed the specific ground, food and shelter the cleared country no longer offered, and most of them are now locally or entirely gone — part of a continental tally in which more than one in ten of Australia’s endemic land mammals has been lost since European settlement, the worst such record on Earth (Woinarski et al. 2015).
Which is the sting in the possum’s tail.
Because it is common and visible, the possum has become, for most people who share a roofline with one, simply what a native mammal looks like — the default “nature” a modern Adelaide child grows up with, alongside the rosella in the gum tree, with no reason to suspect a whole cast of quieter mammals once shared that same backyard.
That is the shifting baseline doing its quiet work again: a genuine, thriving native animal, mistaken for the full picture rather than what it actually is — the one contestant flexible enough to still be standing (Pauly 1995).
Reading the country
Listen for the possum rather than looking for it: a scrabbling overhead at dusk, a rasping, almost mechanical cough from a dark fork in a street tree, chewed rose buds or stripped loquats by morning, and a pair of eyes throwing back torchlight from the canopy at night.
Then ask the harder question the sighting is built to prompt — what else used to den in that same hollow, before there were roofs to den in instead.
Notes & sources
Authored for Reading the Country. General natural history of the common brushtail possum (Trichosurus vulpecula) — physical description, diet, denning habits, nocturnal behaviour and vocalisation — is stated qualitatively as standard field-guide biology; no numeric or contested claim rests on it.
- Shifting baseline. The mechanism by which a common, adaptable species can stand in for “healthy nature” once specialists are gone — Pauly 1995, TREE 10(10):430.
- Mammal-extinction backdrop. More than one in ten of Australia’s ~273 endemic land-mammal species lost since European settlement, the worst continental record on Earth, driven chiefly by introduced foxes and cats plus clearing — Woinarski, Burbidge & Harrison 2015, PNAS 112(15):4531-4540. Used here as the contrast the possum’s persistence is read against, following the same framing given to the region’s mammal losses in Ch 16 (“Reading Absence”).
- Clearance context. The scale of South Australian native-vegetation clearance and forest degradation since colonisation, within which the possum’s den-site substitution (tree hollow to roof cavity) takes place — Bradshaw 2012, J. Plant Ecology 5(1):109-120.
Go deeper — the mechanism & the evidence
What let the common brushtail possum (Trichosurus vulpecula) stay when the bilby, the bettongs and most of the region's other native mammals did not is not luck but flexibility, stacked twice over. It is a dietary generalist, browsing leaves, blossom, fruit, buds and, when the chance presents, a vegetable garden or a rose bush, rather than depending on one plant or one prey type the way a specialist forager must. And it is a den-site generalist: a tree hollow is its ancestral home, but a roof cavity, a stormwater culvert or a shed under a loose sheet of iron will do just as well, because to a possum a dark, enclosed, weatherproof space is a hollow whether a eucalypt or a builder made it. Clearing a landscape strips out both the specific plants and the old hollow-bearing trees a fussier animal needs (Bradshaw 2012) — but it does not remove cavities and vegetation altogether, it just rearranges them into houses and gardens, and a generalist can simply follow the rearrangement. That is exactly the flexibility Australia's more narrowly adapted small and medium mammals lacked, and its absence is a large part of why the continent has lost more than one in ten of its endemic land-mammal species in two centuries, a rate matched nowhere else on Earth (Woinarski et al. 2015). The possum's success is therefore not evidence the clearing was harmless; it is a demonstration of exactly which trait clearing selects for, and a reminder that the animals still visible in a modern garden are the most adaptable survivors of a fauna, not a representative sample of it (Pauly 1995).
Sources for this guide · 3
Every claim here is traceable. Each citation links to its entry in the bibliography.
- Pauly, D. (1995). Anecdotes and the shifting baseline syndrome of fisheries. Trends in Ecology & Evolution 10(10):430. https://doi.org/10.1016/S0169-5347(00)89171-5 — The shifting-baseline mechanism — why a common, adaptable animal can stand in for 'healthy nature' once specialists are gone.
- Woinarski, J.C.Z., Burbidge, A.A. & Harrison, P.L. (2015). Ongoing unravelling of a continental fauna: decline and extinction of Australian mammals since European settlement. PNAS 112(15):4531-4540. https://doi.org/10.1073/pnas.1417301112 — The scale and drivers of Australia's mammal-extinction record, the backdrop the possum's persistence is read against.
- Bradshaw, C.J.A. (2012). Little left to lose: deforestation and forest degradation in Australia since European colonization. Journal of Plant Ecology 5(1): 109–120. DOI: 10.1093/jpe/rtr038. https://doi.org/10.1093/jpe/rtr038 — The scale of vegetation clearance in South Australia the possum's suburban survival is a work-around of.
Concepts this teaches — follow a thread
The shifting baselineClearance and fragmentation (the great clearing)
More guides like this
Adelaide rosellaBanksiaBrush-tailed bettong (woylie)Grasstree (Xanthorrhoea)Greater bilby (the lost suburbanite)Grey mangrove
Test yourself →
The greater bilby, the bandicoots and the bettongs are mostly gone from the cleared Adelaide Plains, yet the common brushtail possum still thumps around in suburban roofs every night. What let the possum stay when its native mammal neighbours could not?
Clearing removes specific foods and old hollow-bearing trees a specialist needs, but it does not remove cavities and vegetation altogether — it just rearranges them into houses and gardens (Bradshaw 2012). A dietary and den-site generalist like the brushtail possum can simply follow that rearrangement, while the bilby, bandicoots and bettongs needed the particular ground, food and shelter the cleared country no longer offered. That contrast is part of a continental pattern in which more than one in ten of Australia's endemic land mammals has been lost since European settlement, the worst such record on Earth (Woinarski et al. 2015).