Apteribis, an extinct species of ibis that once inhabited the Hawaiian Islands, occupied a niche similar to that of the New Zealand kiwi: a nocturnal, flightless bird that relies on tactile cues from its beak to detect prey, according to a new study by scientists from the University of Lethbridge, Flinders University and the Smithsonian National Museum of Natural History.
Apteribis. Image credit: Sarah Citron, University of Lethbridge.
Evolution on islands often generates specialized lifestyles that are rarely seen in continental species.
The biota on oceanic islands are, however, prone to extinctions following human colonization, resulting in an incomplete understanding of the lifestyles of species that evolved prior to colonization.
For example, the Hawaiian Islands hosted a unique and diverse assemblage of endemic species, most of which became extinct following human colonization.
“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,” said Sara Citron, a Ph.D. candidate from the University of Lethbridge.
“But really, ibises are beautiful and distinct birds: they have exceptionally long, elegant beaks and striking colors that set them apart from other shorebirds.”
“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.”
In the study, Citron and her colleagues examined skulls from 25 of the 28 living ibis species from museum collections.
They used advanced imaging technology to create 3D reconstructions of the birds’ brains and compared them with the fossil species.
“What we found was astonishing. 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,” Citron said.
Apteribis’ reduced visual system suggests a nocturnal lifestyle, which is an unprecedented trait among ibises.
The bird likely roamed the Hawaiian landscape under cover of darkness to feed and possibly breed, while resting during the heat of the day.
“Such extreme reductions are known only in a few birds, including the elusive Australian night parrot or New Zealand’s kiwi and kakapo,” said Aubrey Keirnan, a Ph.D. student at Flinders University.
“All of these species rely very little on sight and are active mainly at night.
“The Hawaiian species were targeted because island evolution often produces bizarre anatomies,” said University of Lethbridge’s Dr. Andrew Iwaniuk.
“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.”
“Hawaii is the most isolated archipelago on Earth and originally had no mammalian predators,” said Flinders University’s Dr. Vera Weisbecker.
“Similar to the situation in New Zealand, large birds like ibises were safe on the ground and eventually lost the ability to fly.”
“Accurate sight would not have been a particular advantage.”
The other factor pushing Apteribis into the dark was probably their prey.
“The Hawaiian islands were once home to an extraordinary diversity of snails and flightless crickets,” said Dr. Helen James, curator of birds at the Smithsonian National Museum of Natural History.
“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.”
“Possible causes of extinction are changes to the climate and vegetation on the Hawaiian islands, and the first arrival of humans.”
“The New Zealand kiwi is often seen as an one‑of‑a‑kind oddity among modern birds,” Dr. Iwaniuk said.
“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.”
The study was published in the journal Integrative and Comparative Biology.
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Sara Citron et al. 2026. Comparative Anatomy Supports the Evolution of Nocturnality in the Extinct Hawaiian Ibis Apteribis. Integrative and Comparative Biology 66: icaf159; doi: 10.1093/icb/icaf159