A recently published study reveals that the extinct Hawaiian ibis, Apteribis, possessed unusually small eyes and limited vision, suggesting a largely nocturnal lifestyle. Researchers from the University of Lethbridge, Flinders University, and the Smithsonian National Museum of Natural History discovered this through detailed analysis of fossil skulls and comparisons with modern ibis species. The findings, published in Integrative and Comparative Biology, shed light on how island evolution can drive unique adaptations, and how much biodiversity has been lost before science could fully document it.
The Evolution of Nocturnality in Island Species
Island ecosystems often produce specialized species rarely seen elsewhere. Apteribis appears to have followed a similar evolutionary path to the New Zealand kiwi, becoming flightless and relying on tactile cues from its beak to detect prey in the dark. This adaptation is particularly striking given that ibises are typically diurnal birds with highly developed vision.
“The Hawaiian Islands provided an ideal setting for such extreme evolution,” explains Dr. Andrew Iwaniuk of the University of Lethbridge. “The lack of mammalian predators meant there was little selective pressure to maintain strong flight or sharp eyesight.”
How Apteribis Fed in the Dark
The study found that the imprints of the visual system on Apteribis skulls were dramatically reduced compared to living ibis relatives. The orbits, where the eyes sat, were smaller than expected, and the optic nerve and brain structures responsible for processing light were underdeveloped. This suggests the bird likely foraged at night, probing for prey in mud or soft ground using its long, sensitive beak.
According to Dr. Helen James, curator at the Smithsonian, “The Hawaiian Islands once hosted a wealth of nocturnal invertebrates, including snails and flightless crickets, which likely drove Apteribis to adopt a nighttime foraging strategy.”
A Lost Ecological Role
The extreme reduction in vision in Apteribis is comparable to the adaptations seen in other nocturnal birds like the Australian night parrot and New Zealand’s kiwi and kakapo. The Hawaiian ibis demonstrates that such evolutionary pathways can occur independently across different island ecosystems.
“This extinct ibis shows that similar forms evolved elsewhere, reminding us how much diversity has been lost, and how many ecological roles disappeared, before we ever had the chance to study them,” Dr. Iwaniuk adds. The extinction of Apteribis, likely due to climate change and human colonization, represents a significant loss of unique biodiversity.
The research underscores the fragility of island ecosystems and the importance of studying extinct species to understand the full extent of evolutionary processes.
