A species · Bird
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.
- On the gradient
- The wet spine — Mount Lofty forest canopy, feeding on the ranges' banksia and hakea and nesting in its oldest hollow-bearing trees
- Rock
- Uplifted, deeply weathered Neoproterozoic (Adelaidean) bedrock along the Mount Lofty Ranges scarp block
- Soil
- Leached, acid duplex soils (Kurosols) under the old-growth stringybark and messmate forest it nests in
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What you'll take away
- Recognise the yellow-tailed black-cockatoo by its size, wailing call and feeding sign — shredded banksia and hakea cones, raggedly chiselled dead wood — rather than a fleeting glimpse of the bird itself.
- Explain why the cockatoo depends on two increasingly scarce resources at once: old hollow-bearing trees to nest in, and seed-bearing shrubs to feed on, both of which a cleared and 'tidied' forest struggles to keep.
- Connect the cockatoo's decline to the Mount Lofty Ranges' extinction debt — a fragmented forest that still holds the bird today but has not secured its future.
Some birds announce themselves before you ever see them. Long before a yellow-tailed black-cockatoo comes into view over a Mount Lofty ridgeline, you hear it — a long, creaking, faintly mournful wail passed back and forth between the members of a loose, unhurried flock. Mournful enough that the naturalists who named the species called it funereus, “of the funeral,” and once you have heard that call drifting down a gully at dusk you understand exactly why. Then the birds themselves come over: heavy, slow-beating, better than half a metre from beak to tail, sooty black all over but for a yellow cheek patch and a yellow flash through the tail that shows only in flight. They are unmistakable, and once you know the call, unmissable.
What the flock is doing up there is worth watching for. It will settle into a stand of banksia or hakea and get to work with a pair of pliers disguised as a beak, shredding cone after cone for the seed inside and leaving the ground littered with chewed husks — a sure sign, if you find the litter, of a recent visit even once the birds have moved on. The same beak turns to dead timber, levering off bark and wood to reach the grubs of wood-boring beetles tunnelling underneath, so that a raggedly excavated dead limb is often as much the cockatoo’s calling card as the bird itself.
That bill can crack a banksia cone in a second, but it cannot conjure a nest hollow, and this is where trouble starts for the bird. A cavity deep enough to raise a cockatoo chick takes a eucalypt the better part of a century to grow, and a forest logged, cleared for pasture or tidied for firewood since the 1840s has had precious little time to grow one. Layer that onto a forest already declining bird by bird — the Mount Lofty woodland community losing more than half its species over sixteen years of careful counting, with roughly ten already gone for good (Prowse et al. 2021) — and the cockatoo turns out to be exactly the kind of large, slow-breeding, wide-ranging species that ecologists expect to be among the last to disappear and the hardest to bring back: part of a debt the ranges’ clearing opened generations ago and is still, quietly, calling in (Szabo et al. 2011).
The wail still carries over the ridgelines most weeks you go looking. What it is announcing, more and more, is scarcity.
Go deeper — the mechanism & the evidence
The yellow-tailed black-cockatoo is a demanding bird twice over, which is what makes it such a sensitive read on forest health. As a large-hollow nester it needs a cavity deep enough to raise a chick in, and in Mount Lofty stringybark and messmate forest that size of hollow only starts forming once a eucalypt is on the order of a century old — a threshold few trees have been left standing long enough to reach, in a landscape logged, ring-barked or cut for firewood since the 1840s (Armstrong et al. 2003). Layered onto that is a forest already emptying by measured stages: cleared, altered or cut into fragments across something like nine-tenths of its original extent, the ranges' woodland-bird community is paying out what ecologists call an extinction debt, with roughly ten species already regionally lost and more than half of what remains still declining across sixteen years of standardised survey (Szabo et al. 2011; Prowse et al. 2021). A large-bodied, wide-ranging, slow-breeding bird like the cockatoo sits exactly among the species that arithmetic predicts will be last to vanish and hardest to bring back — which is precisely why finding one today reads less like reassurance than like a countdown still running.
Sources for this guide · 3
Every claim here is traceable. Each citation links to its entry in the bibliography.
- Armstrong, D.M., Croft, S.J. & Foulkes, J.N. (2003). A Biological Survey of the Southern Mount Lofty Ranges, South Australia, 2000–2001. Department for Environment and Heritage, South Australia. https://data.environment.sa.gov.au/Content/Publications/Southern-Mount-Lofty-Ranges-BioSurvey.pdf — Biological survey of the southern Mount Lofty Ranges — the forest structure and old-tree habitat the cockatoo depends on.
- Szabo, J.K., Baxter, P.W.J., Vesk, P.A. & Possingham, H.P. (2011). Paying the extinction debt: woodland birds in the Mount Lofty Ranges, South Australia. Emu — Austral Ornithology 111(1): 59–70. DOI: 10.1071/MU09114. https://www.publish.csiro.au/mu/mu09114 — The Mount Lofty Ranges' woodland cleared/fragmented to roughly a tenth of its extent, and the extinction-debt modelling among its birds.
- Prowse, T.A.A., O'Connor, P.J., Collard, S.J., Rogers, D.J. & Litchfield, C. (2021). Optimising monitoring for trend detection after 16 years of woodland-bird surveys. Journal of Applied Ecology 58(6): 1090–1100. (Author list to confirm.) DOI: 10.1111/1365-2664.13860. https://doi.org/10.1111/1365-2664.13860 — Sixteen years of woodland-bird monitoring confirming ongoing decline across the ranges.
Concepts this teaches — follow a thread
The extinction debtClearance and fragmentation (the great clearing)
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Part of these pathways
Test yourself →
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).