Apteribis, a now-extinct avian species that once populated the Hawaiian archipelago, occupied an ecological niche strikingly analogous to that of the New Zealand kiwi. Emerging from a recent scientific investigation conducted by researchers from the University of Lethbridge, Flinders University, and the Smithsonian National Museum of Natural History, the findings indicate that this flightless bird was primarily active during nocturnal hours and relied on tactile sensory input via its beak to locate sustenance.
Apteribis. Image credit: Sarah Citron, University of Lethbridge.
The phenomenon of island biogeography frequently engenders the evolution of highly specialized life forms, seldom observed in species originating from continental landmasses.
However, the faunal communities of remote oceanic islands are particularly vulnerable to extirpation subsequent to human settlement, thereby creating lacunae in our comprehension of the ecological behaviors of species that predated such introductions.
Illustratively, the Hawaiian Islands were once home to a rich and heterogeneous collection of indigenous organisms, the vast majority of which vanished after the archipelago was inhabited by humans.
“The ancestral lineage of Apteribis was related to the Australian white ibis, a bird colloquially termed the ‘bin chicken’ due to its propensity for foraging through refuse containers with its bill,” remarked Sara Citron, a doctoral candidate at the University of Lethbridge.
“Nevertheless, it is important to recognize that ibises are inherently elegant and distinctive avians, characterized by exceptionally elongated, refined bills and vibrant plumage that distinguishes them from other wading birds.”
“Their elongated rostrums are instrumental in their feeding methodology. By submerging their beaks into substrate such as mud, shallow aquatic zones, or yielding earth, they actively search for minute disturbances that betray the presence of concealed sustenance, for instance, small invertebrate organisms.”
In the course of their research, Citron and her collaborators meticulously analyzed cranial specimens from 25 out of the 28 extant ibis species, sourced from various museum archives.
Employing cutting-edge imaging technologies, they generated three-dimensional reproductions of the birds’ cerebral structures, facilitating a comparative analysis with the fossilized species.
“The discoveries we made were truly remarkable. All indicators of the visual apparatus on the skull—encompassing the ocular cavities, the optic nerves, and the optic tectum region responsible for neural light processing—exhibited significant diminishment in Apteribis when contrasted with its contemporary relatives,” stated Citron.
The characterized reduction in the visual system of Apteribis strongly implies a nocturnal adaptation, a characteristic previously undocumented among ibis species.
It is probable that this creature traversed the Hawaiian terrain under the cloak of darkness for foraging and potentially for reproductive activities, seeking refuge during the peak daylight hours.
“Such pronounced anatomical regressions are documented in only a select few avian species, including the seldom-seen Australian night parrot and New Zealand’s kiwi and kakapo,” explained Aubrey Keirnan, a doctoral student affiliated with Flinders University.
“These particular species exhibit a minimal reliance on visual perception and are predominantly active during nighttime hours.
“The Hawaiian endemic species were selected for investigation due to the tendency for island evolution to produce peculiar anatomical configurations,” observed Dr. Andrew Iwaniuk from the University of Lethbridge.
“From the initial examination of the skull, it was evident that the orbits, the skeletal depressions housing the eyes, were considerably smaller than anticipated.”
“The Hawaiian archipelago represents the planet’s most geographically remote island chain and historically lacked native mammalian predators,” noted Dr. Vera Weisbecker of Flinders University.
“Analogous to the circumstances in New Zealand, large ground-dwelling birds such as ibises were afforded protection from predation, consequently leading to a gradual loss of their capacity for flight.”
“Consequently, acute visual acuity would not have conferred a significant evolutionary advantage.”
An additional contributing factor likely compelling Apteribis to adopt crepuscular or nocturnal habits was the nature of its dietary sources.
“The Hawaiian Islands once supported an extraordinary array of terrestrial gastropods and flightless orthopterans,” commented Dr. Helen James, the curator of ornithology at the Smithsonian National Museum of Natural History.
“These ground-dwelling crickets and snails were primarily nocturnal, and their abundance would have been greater during that epoch, presenting precisely the type of prey that could have incentivized a species like Apteribis to transition to nighttime foraging.”
“Potential catalysts for its extinction include climatic shifts and modifications to the vegetative landscape of the Hawaiian islands, alongside the initial advent of human presence.”
“While the New Zealand kiwi is often regarded as a singular anomaly among extant avian species,” Dr. Iwaniuk stated.
“This extinct ibis demonstrates that analogous evolutionary pathways have transpired in other isolated environments.”
“It serves as a potent reminder of the substantial biodiversity that has been irrevocably lost, and the multitude of ecological roles that consequently ceased to exist, prior to our opportunity to scientifically document them.”
The research publication detailing these findings has been formally released in the scientific 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
