Perth, Feb 9: The bird many Australians dismiss as a nuisance — the Australian white ibis, nicknamed the “bin chicken” — is closely related to a remarkable Hawaiian cousin that has since gone extinct: a flightless ibis so visually reduced it was likely adapted to life in near-darkness.
A new international study led by researchers at the University of Lethbridge in Canada and Flinders University in Australia examined the skull of Apteribis, an extinct flightless ibis that once lived on the Hawaiian islands, and found evidence of unusually small eyes and limited visual capacity.
Lead author Sara Citron said Apteribis belonged to the same broader ibis family as the Australian white ibis, but stressed the group’s distinctive traits are often overlooked.
“Apteribis was a relative of the Australian white ibis, commonly known as ‘bin chicken’ for their habit of rifling through rubbish bins with their beak. But really, ibises are beautiful and distinct birds: they have exceptionally long, elegant beaks and striking colours that set them apart from other shorebirds,” says Ms Citron, a PhD candidate from the University of Lethbridge Iwaniuk Lab.
“Their elongated beaks are key to how they feed. By inserting the beak into mud, shallow water, or soft ground, they probe for subtle vibrations that reveal the presence of hidden prey, such as small invertebrates,”
Using museum specimens from around the world, the researchers examined skulls from 25 of the 28 living ibis species, then used advanced imaging technology to build 3D reconstructions of the birds’ brains, comparing them with the fossil species.
“What we found was astonishing,” Ms Citron says. “All imprints of the visual system on the skull – like the eyes, the optic nerve, and the optic tectum area where light is processed by the brain – were dramatically reduced in Apteribis compared to its living relatives.”
Flinders University co-author Aubrey Keirnan said reductions of this magnitude are rare, and are typically associated with birds that rely less on sight.
“Co-author Aubrey Keirnan, a PhD student at Flinders University, says that such extreme reductions are known only in a few birds, including the elusive Australian night parrot or New Zealand’s kiwi and kakapo.
“All of these species rely very little on sight and are active mainly at night,” says Keirnan, from the College of Science and Engineering at Flinders University.”
Based on the skull evidence, the researchers say Apteribis was likely nocturnal, moving through the Hawaiian landscape at night to feed — and possibly breed — while resting during the day.
Senior author Associate Professor Andrew Iwaniuk said the team targeted Hawaiian species because island evolution often produces unusual anatomies.
“From the moment we looked at the skull, we could see that the orbits, the spaces where the eyes sit, were far smaller than they should have been,” he says.
Flinders University Associate Professor Vera Weisbecker said Hawaii’s extreme isolation — and the historical absence of mammalian predators — likely shaped the bird’s evolution.
“Similar to the situation in New Zealand, large birds like ibises were safe on the ground and eventually lost the ability to fly,” says Associate Professor Weisbecker. “Accurate sight would not have been a particular advantage.”
The researchers also suggest the bird’s prey may have pushed it further into nocturnal habits. Helen James, Curator of Birds at the Smithsonian National Museum of Natural History, said the islands once supported abundant nocturnal food sources such as snails and flightless crickets.
“Flightless crickets and snails are nocturnal and would have been more abundant then, exactly the kind of prey that could drive a bird like Apteribis to adopt night-time foraging,” explains Dr James, who is also part of the research team.
The study notes possible causes of Apteribis’ extinction include climate and vegetation changes and the arrival of humans in the Hawaiian islands.
Professor Iwaniuk concludes: “The New Zealand kiwi is often seen as a one-of-a-kind oddity among modern birds. But this extinct ibis shows that similar forms evolved elsewhere.
“It reminds us how much diversity has been lost, and how many ecological roles disappeared, before we ever had the chance to study them.”
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