Field Museum researchers make new discoveries on Hawaiian bird with "Swiss Army beak"

A new study using data from Chicago's Field Museum of Natural History helped uncover how an endangered Hawaiian bird uses its body to drill for food.

An endangered yellow bird called an 'akiapōlāʻau (pronounced "Ah-key-ah-pole-ah-ow"), or Aki, evolved its so-called "Swiss Army beak" to drill into branches to find food. The bill is so called because it is used as two separate tools, and looks like two different birds' bills "Frankensteined" together, the museum said.

"The Aki is unique from every other bird that has ever evolved, and not just in Hawaii — it has features unseen in any birds," lead author of the study, University of Chicago Ph.D. candidate Alexander Clark, said in the release.

The upper bill is long, narrow, and flexible so it can probe grubs and caterpillars out of nooks and holes in branches, the museum said. The bottom mandible is short and broad and used for boring into wood.

This makes the Aki similar to a woodpecker, a bird that is not found in the Hawaiian Islands.

"For a bird like the 'akiapōlāʻau to evolve, there had to have been intense competition in the ecosystem," Paul Banko, co-author of the study and former researcher at the USGS Pacific Island Ecosystems Research Center in Hawaii, said in the release. "When the island of Oahu emerged from under the water, there was a relatively large explosion of animal species. This was undoubtedly due to the different species competing for valuable resources, like caterpillars, to feed their young."

Scientists already knew about the bill. What they didn't know was just how the Aki uses its bill to bore into wood and hunt for insects without getting injured.

"We knew what they're doing, but we didn't quite know anatomically how their body is facilitating those movements. How are they actually doing it?" Clark said in the release. "And now, we have a pretty good idea."

It turns out the Aki actually uses its whole body along with its bill when drilling for food. A large tendon in the bird's ankle allows the bird to bring its whole body downward quickly and forcefully, making it possible for the bird to gouge into wood.

This is unlike woodpeckers, which primarily use their neck muscles for such purposes, the museum said.

Clark, explained that the movement is like swinging an axe. He said the bird uses its whole body, starting with the upward bending its ankles, while also anchoring itself to what it's pounding into.

The study comes at a critical time, with experts estimating there are less than 2,000 Aki left in the wild.

It highlights the unique features of a bird only found on the northeastern slope of one mountain in the island of Hawaii.