Pathway · about 20 minutes · 7 steps
The wet island
Read the Mount Lofty refugium — a wet island marooned in a drying sea of country, and the birdsong going quiet in it.
Start at the top, because this is the one place the whole argument is visible at once. From the summit lookout the gulf shimmers one way and the mallee fades out dry the other, and in between sits a damp green sliver that shouldn’t, by the rules of this climate, exist at all. Walk down into it: first the stringybark forest, that sliver’s spine, then its deepest, dampest creases, the fern gullies, cool and improbable, a rumour of rainforest that never quite left. Lower again, into the Fleurieu’s spring-fed peat swamps, the wettest ground the ranges have to offer and the last redoubt of a few particular lives. Then meet three of them: the southern emu-wren threading the sedge, the chestnut-rumped heathwren holding on in isolated pockets of heath, and the yellow-tailed black-cockatoo wailing overhead, needing old hollows the forest is running out of. Each bird is a gauge of how much refuge is left.
Take it with you. Next time you’re under stringybarks, listen for what isn’t there as much as what is — an island keeps its shape long after some of its residents have quietly gone. Close the page and go outside.
- Mount Lofty summit — A railed lookout a little over 710 m above the plains where, on a clear day, the whole gulf-to-range argument of the book lies open in front of you at once.
- Stringybark country — The forested spine of the Mount Lofty Ranges — a wet island of the past, marooned by drought and holding on, that is quietly emptying of its woodland birds.
- The fern gullies — The deepest, dampest creases of the ranges — permanent-shade creek gullies of tree ferns and one-cell-thick filmy ferns, the faint, diminished cousins of rainforest holding on inside a Mediterranean summer.
- The Fleurieu peat swamps — Spring-fed peat swamps in the wettest folds of the southern ranges — an acid sponge built by centuries of waterlogging, and the last stronghold of the Mount Lofty southern emu-wren.
- The southern emu-wren — A tiny, secretive bird with a filamentous tail like six wisps of a moulting emu, bound to the dense sedgy swamps of the high Fleurieu and Mount Lofty country — a living token of the ranges' wet refuge, and of how little of it is left.
- The Mount Lofty chestnut-rumped heathwren — A ground-hugging bird of the wet heath, so isolated in the Mount Lofty Ranges that it has become its own endemic race — known from only a handful of sites, and undone by exactly what undoes the emu-wren beside it: open ground, and shrinking cover.
- Yellow-tailed black-cockatoo — The great wailing, half-metre-long hollow-nester of the Mount Lofty forests — doubly dependent on old trees and seed-bearing shrubs a tidied, fragmenting forest is running short of, and sliding as both disappear.
The end-check — put it together
You've walked the steps. Now answer these from what the pathway taught, not from the pages — getting them here is what tells you it stuck.
The southern emu-wren is a weak-flying skulker found only in the dense, wet sedge swamps of the high Fleurieu and southern Mount Lofty country. What does finding one actually tell you about the swamp you're standing in, and why is it so easily lost from it?
The southern emu-wren is a moisture-demanding relict tied to the dense sedgeland and heath of valley-floor swamps in the high, rainy Fleurieu and southern Mount Lofty country (Armstrong, Croft & Foulkes 2003). Its close relative, the mallee emu-wren, is the dry-country counterpart living the same skulking life in spinifex behind the ranges — the two sort onto opposite ends of the region's water gradient. Because the Fleurieu swamps have been drained, cleared and squeezed by a drying climate, the southern emu-wren is among the first birds to disappear once its cover is broken, making it a textbook carrier of the Mount Lofty Ranges' 'extinction debt' (Szabo, Baxter, Vesk & Possingham 2011).
The Mount Lofty chestnut-rumped heathwren is known from only about eight sites, strung from Tanunda in the north to Deep Creek in the south — more than a hundred kilometres apart. Why does the book treat that scatter of surviving sites as a countdown clock rather than good news?
Extinction debt is the idea that habitat clearing and fragmentation can commit a population to decline well before the losses are counted; the heathwren's eight isolated dots across the whole range, with no corridor of livable heath left between them, is exactly that pattern — present, but on a trajectory the clearing already set (Szabo et al. 2011). The population is also its own endemic race, parkeri, cut off long enough by disjunction to be found nowhere else on Earth (Armstrong, Croft & Foulkes 2003).
The yellow-tailed black-cockatoo depends on two quite different resources at once — one to nest in, one to feed on. What are they, and why does that combination make it a poor fit for a forest that has been cleared or 'tidied'?
A nest hollow big enough for a cockatoo chick only forms once a Mount Lofty eucalypt is on the order of a century old, and the bird's staple food is the shredded cones of banksia and hakea shrubs — so it needs both an old-growth canopy and an intact shrub layer at the same time. Clearing, logging or 'tidying' a forest removes its oldest trees and its understorey first, which is exactly why a double-dependent species like this reads as such a sensitive indicator of forest health (Armstrong, Croft & Foulkes 2003).