Endangered ʻakiapōlāʻau uses its whole body to gouge wood for food

The endangered ʻakiapōlāʻau uses its beak and body to open branches and reach insect larvae on Hawaii island, according to new research reported by Reuters on Nov. 5. The findings describe how the bird’s legs help drive its wood-gouging movement, adding anatomical detail to a feeding behavior that fills a niche occupied by woodpeckers elsewhere.

How the ʻakiapōlāʻau opens wood

Found only on Hawaii, the honeycreeper feeds mainly on insects, including larvae hidden in branches. Hawaii has no native woodpeckers, and the ʻakiapōlāʻau has evolved a similar way to reach prey in wood, despite not being closely related to them, Reuters reported.

The two parts of the beak serve different roles: the lower bill is short and stout for gouging, while the long, slender upper bill reaches into openings for grubs and caterpillars. Beneath its outer covering, the upper bill’s bony structure is about 38 percent shorter, leaving a section that can flex as the bird probes, Reuters reported.

Why the legs matter during each strike

Researchers also found that the bird has a proportionally short femur, the upper leg bone. Lead author Alexander Clark, a University of Chicago Ph.D. candidate affiliated with the Field Museum, said shorter legs may lower the bird’s center of gravity as it clings to awkward perches. Reuters reported that the skeleton also has a well-developed attachment for a muscle that flexes the ankle. Clark described the muscle as helping lift and drive the body during gouging.

Clark characterized the strikes as whole-body movements, in contrast with woodpeckers’ mainly neck-driven drilling. Researchers have not fully worked out how the ʻakiapōlāʻau’s skull withstands repeated impacts. Clark said it has a structure resembling one in woodpeckers, but that feature is less developed in the honeycreeper, Reuters reported.

What museum specimens reveal about the endangered bird

For the Reuters-reported study, researchers examined three ʻakiapōlāʻau skeletons held by the University of California, Berkeley’s Museum of Vertebrate Zoology and compared them with related continental finches from other museum collections. The Field Museum account published by Phys.org says the study drew on measurements of historical specimens across three institutions.

The Field Museum account estimates that fewer than 2,000 ʻakiapōlāʻau live in the wild, on the northeastern slope of a single mountain on Hawaii. That figure is an estimate reported by the museum, not a census presented in its account. The bird’s restricted range and specialized feeding method place the anatomical findings in the context of a species found nowhere else.