The Bass Strait region is well-known for its rugged coastlines, beautiful landscapes, and, of course, cheese. Lesser known, but arguably more important, are the unique and endangered birdlife that call the region home.
The islands of the Bass Strait share many bird species with the Lutruwita/Tasmanian and Australian mainland. However, there are several avian anomalies in the region’s biogeography (the study of species distribution in geographic space and time).
Here, I explore just a few of these strange occurences, including unusual avian distributions, missing feathered species, and unique subspecies.
A battle of altitude and islands
The Lutruwita/Tasmanian mainland is home to two species of the lovable and long-beaked big black birds, the currawong.
The black currawong (Strepera fuliginosa) is an iconic Tasmanian bird. It is found only on the Lutruwita/Tasmanian mainland and its offshore islands, meaning it is ‘endemic’ to this region. With their evident intelligence and distinctive yellow eyes, the bird is found at higher altitudes on the Lutruwita/Tasmanian mainland and is a common backpack thief for mountain-rambling bushwalkers.
On the other hand, the grey currawong (Strepera versicolor), also known as the clinking currawong (take a listen to their call to know why), is widespread across south-eastern Australia, including Lutruwita/Tasmania. However, this grey cousin is completely absent from the Bass Strait islands.
About the Author
With thanks to
University of Tasmania and the Australian Research Council Centre of Excellence for Australian Biodiversity and Heritage (CABAH)
The black currawong is found only in Lutruwita/Tasmania and its offshore islands. Photograph by DH Fischer. CC BY-NC 4.0.
The grey currawong is found in Lutruwita/Tasmania and mainland Australia but is absent from the Bass Strait islands. Photograph by Patrick Kavanagh. CC BY 2.0.
On the Bass Strait islands, the black currawong dominates all elevations, often found from the tall peaks of Mt Strzelecki on Flinders Island, down to the coastal cattle paddocks.
Why might the adaptable grey currawong be absent from the Bass Strait islands? Presumably black and grey currawongs had similar access to the region when it was once a land bridge. And what stops these large birds from hopping from island to island?
This puzzle remains unsolved. One theory is that the islands only have finite resources, and the black currawong was able to fill the ecological niche of its grey cousin and therefore exclude them.
Despite being the exclusive currawongs of the islands, black currawong populations in the Bass Strait are experiencing declines in the face of continuous land clearing, a threat to many species in the area.
The real-life angry birds
Lutruwita/Tasmania is lucky enough to have its very own endemic scrubwren, the aptly named Tasmanian scrubwren (Sericornis humilis). This real-life angry bird (thanks to their strong brow) is often hard to spot amongst the dense scrub it occupies, yet it is easy to hear with its cranky high-pitched chirp.
While the distribution of Lutruwita/Tasmania’s endemic birds is varied across the many islands of the Bass Strait, the case of the scrubwren is special.
In addition to the Lutruwita/Tasmanian mainland, the Tasmanian scrubwren can be found on King Island, the western island of the Bass Strait. However, on Tayaritja/the Furneaux Group of Islands in the east, the species is missing, replaced by its Australian mainland counterpart, the white-browed scrubwren (Sericornis frontalis).
So, how did they get there? These small birds love dense scrub. But it’s thought that the western plains around King Island, now underwater, had massive stretches devoid of scrub. The eastern bridge was the obvious access route for the birds given the shorter distances between the precious scrub they admire.
Were they able to fly over extensive expanses, much like the array of birds that annually migrate across the strait in the present day? Another mystery to add to the records.
The Tasmanian scrubwren is found only in Lutruwita/Tasmania and on King Island in the western Bass Strait. Photograph by Heidi Krajewsky. CC BY-NC 4.0.
The white-browed scrubwren lives in mainland Australia and is also found on Tayaritja/the Furneaux Group of Islands in the eastern Bass Strait. Photograph by Patrick Kavanagh. CC BY 2.0.
The curious case of the missing emu
Today emus are only found on mainland Australia, but when Europeans first invaded there were emus roaming Lutruwita/Tasmania and King Island. Photograph by Rob Ellis. CC BY 2.0.
What route did emus take across the Bass Strait land bridge? Photograph by Paul Coddington. CC BY 4.0.
The lovable, yet somewhat intimidating, emu (Dromaius novaehollandiae) is as iconic to Australia as BBQs, Australian Rules football and big red kangaroos.
Despite their status, many are unaware that emus once roamed both Lutruwita/Tasmania and King Island. However, shortly after the European occupation of the area, the southern emus met their demise due to overhunting.
You might be wondering how these flightless birds managed to migrate down to Lutruwita/Tasmania and King Island. Presumably they walked across the Bass Strait land bridge before it was submerged by rising sea levels, but their path remains a mystery. So what evidence do we have to solve the case?
Firstly, the King Island emu subspecies (D. n. minor) was a dwarf bird half the size of modern-day emus. It is common for species isolated on islands to evolve into smaller species, suggesting emus were on King Island for a reasonably long time before their extinction.
Secondly, there are no written records of emus in north-western Tasmania, the region closest to King Island (contrary to paintings of them at Stanley, and Burnie’s main waterway having their namesake, Emu River).
Interestingly, there is also limited evidence, other than a few eggshell deposits on Prime Seal Island, that suggest emus roamed the eastern side of the Bass Strait. This is despite the eastern bridge persisting for many thousands of years longer than the west, and the habitat being presumably quite suitable for our large emu friends.
If the Tasmanian subspecies (D. n. diemenensis) arrived in the state via the eastern front, why is there such little evidence? And why isn’t there a Flinders Island subspecies like there was a King Island subspecies?
One hypothesis is that if emus once roamed Tayaritja/the Furneaux Group of Islands, they were gone before any written records. Lost to a changing climate and environment, or perhaps overhunted by passing seafarers and the past occupants of the islands.
Unfortunately, the emus bring more questions than answers. Yet another cold case in the mysterious Bass Strait.
Tasmanian scrubwren distribution, shown in shaded pale red. Illustration by Jary Nemo. CC BY-NC-ND.
Black currawong distribution, shown in shaded pink. Illustration by Jary Nemo. CC BY-NC-ND.
White-browed scrubwren distribution, shown in shaded dark blue. Illustration by Jary Nemo. CC BY-NC-ND.
Grey currawong distribution, shown in orange. Illustration by Jary Nemo. CC BY-NC-ND.
Emu distribution, shown in bright blue/green with a question mark in the northwest of the Lutruwita/Tasmanian mainland. Illustration by Jary Nemo. CC BY-NC-ND.
The importance of solving these biogeographical mysteries
For some birds in the Bass Strait, isolation on the islands has led to the evolution of unique subspecies, many of which are currently listed as endangered.
Some, such as the King Island scrubtit (Acanthornis magnus greenianus) and King Island brown thornbill (Acanthiza pusilla magnirostris) have been identified, alongside the orange-bellied parrot (Neophema chrysogaster), as the top three Australian birds most likely to go extinct next – not exactly a desirable title.
Ongoing work by the Difficult Bird Research Group at Australian National University is looking into the genetics of these little brown birds (and one bright green parrot) under threat.
The group aims to identify how distinct they are from their Lutruwita/Tasmanian and Australian mainland cousins, information which could guide conservation management and recovery actions for these species.
In the end, uncovering at least one piece of the puzzle will get us one step closer to understanding the ancient Bass Strait land bridge, and help us preserve what now remains.
The threatened orange-bellied parrot, which migrates through King Island in the western Bass Strait, is thought likely to go extinct next. Photograph by Philip Dobbin. CC BY-NC 4.0.
Copyright information
Released under a Creative Commons Attribution Non Commercial No Derivatives 4.0 International (CC BY-NC-ND 4.0) license.
This story is subject to disclaimers, copyright restrictions, and cultural clearances. Copyright © Matthew Fielding, 2024.
Further reading
Birddata, a website containing scientific collection data on Australian birds, BirdLife Australia, accessed 22 March 2024.
Derham T, Johnson C, Martin B, Ryeland J, Ondei S, Fielding M and Brook BW (2023) ‘Extinction of the Tasmanian emu and opportunities for rewilding’, Global Ecology and Conservation, 41:e02358.
Difficult Bird Research Group, Australian National University, Canberra, accessed 24 April 2024.
iNaturalist, worldwide biodiversity observation website, accessed 22 March 2024.
Geyle HM, Woinarski JCZ, Baker GB, Dickman CR, Dutson G, Fisher DO, Ford H, Holdsworth M, Jones ME, Kutt A, Legge S, Leiper I, Loyn R, Murphy BP, Menkhorst P, Reside AE, Ritchie EG, Roberts FE, Tingley R and Garnett ST (2018) ‘Quantifying extinction risk and forecasting the number of impending Australian bird and mammal extinctions’, Pacific Conservation Biology, 24:157-167.
Hume JP, Steel L, Middleton G and Medlock K (2018) ‘In search of the dwarf emu: a palaeontological survey of King and Flinders islands, Bass Strait, Australia’, Cont. Ci. Mus. Arg. Ci. Nat., 7:81–98.
Thomson VA, Mitchell KJ, Eberhard R, Dortch J, Austin JJ and Cooper A (2018) ‘Genetic diversity and drivers of dwarfism in extinct island emu populations’, Biology Letters, 14:20170617.
Webb MH, Holdsworth M, Stojanovic D, Terauds A, Bell P and Heinsohn R (2016) ‘Immediate action required to prevent another Australian avian extinction: the King Island scrubtit’, Emu – Austral Ornithology, 116(3):223-229.
