The ʻakiapōlāʻau, an endangered Hawaiian honeycreeper, has long puzzled scientists. It fills an ecological niche like a woodpecker, though no woodpeckers exist on the Hawaiian islands. A new study published in the journal Ornithology reveals the bird’s success depends on a unique, “whole-body” foraging approach using anatomical adaptations beyond its beak.
How the Beak Works
The ʻakiapōlāʻau is nicknamed the Swiss Army Knife of the Hawaiian islands.
It possesses a dual-purpose bill.
The lower mandible is short and stout. It is designed for vigorously gouging holes into wood.
The upper bill is long, slender, and flexible. It allows the bird to probe for insect larvae within narrow nooks.
Lead author Alexander Clark is a doctoral candidate at the University of Chicago. He is also a scientific affiliate with the Field Museum.
Clark noted that the upper bill’s internal structure is roughly 38% shorter than its outer keratin covering. This bony discrepancy allows the tip to flex safely while the bird searches for prey. When I’ve witnessed this behavior, I could’ve sworn it was going to snap its bill – and yet, it doesn’t,
Clark observed.
Generating Foraging Force
Woodpeckers primarily rely on neck muscles to lunge at surfaces. In contrast, the ʻakiapōlāʻau utilizes its entire body to generate force.
Researchers discovered that the bird’s legs serve as the anchor system for its hammering movements. The bird features a proportionally short femur. This helps lower its center of gravity while clinging to branches in awkward, demanding positions.
The study identified a well-developed attachment for a muscle that flexes the ankle. By contracting this muscle, the bird lifts its body and drives it forcefully downward. It uses its legs to initiate the strike. In ʻakiapōlāʻau, it’s a whole-body affair,
Clark explained. Like effectively swinging an axe, you have to put your whole body into it.
Evolutionary Pressures on the Species
Researchers examined three ʻakiapōlāʻau skeletons from the Museum of Vertebrate Zoology at the University of California, Berkeley. They compared these to related continental finches.
These findings show the extreme evolutionary pressures that shaped the bird. It adapted to compete for limited resources within a unique island ecosystem.
Mastery of these foraging techniques requires coordination. Young birds remain with adults for an unusually long period to practice.
As the species faces the threat of extinction, researchers emphasize documenting these behaviors while the birds are still alive. There will never again be a time in Earth’s history when their songs will make up part of the dawn chorus,
Clark said.
The study was supported by collections at the UC Berkeley museum of zoology, the Washington University Burke Museum, and the Field Museum. These institutions hold the largest biological collections of Hawaiian honeycreepers that have ever been archived.