Meet Hawaii's rare bird with a 'Swiss Army knife' beak that uses its whole body to drill into trees

Imagine a bird that carries two different tools in its beak: one designed to drill into wood and another to pull insects out of the holes. Now imagine that its entire body, right down to its ankles, is built to help it do the job. Meet the 'akiapōlāʻau (pronounced ah-key-ah-pole-ah-ow), a small, yellow bird found only in Hawaii. In an archipelago where woodpeckers are absent, this remarkable species has evolved its own way of tapping into tree branches and hunting for insects hidden beneath the bark. Its unusual beak has earned it the nickname the 'Swiss Army Knife of the Hawaiian islands'. But a new study published in the journal Ornithology has revealed that the bird's extraordinary feeding ability goes far beyond its beak.

Researchers have found that its legs, ankles and body mechanics all work together to help it drill into wood. The discovery offers a fascinating look at how evolution can produce specialised adaptations in isolated ecosystems. It also draws attention to the precarious future of a bird that scientists estimate has fewer than 2,000 individuals left in the wild. A BEAK THAT WORKS LIKE TWO DIFFERENT TOOLS At first glance, the 'akiapōlāʻau's beak looks unusual because its upper and lower parts are strikingly different. The upper bill is long, slender and flexible. It is used to probe narrow openings in tree branches and extract insects such as grubs and caterpillars hiding inside.

The lower mandible, meanwhile, is shorter and stronger. It acts more like a chisel, helping the bird gouge holes into wood to reach its prey. Together, these two distinct structures allow the 'akiapōlāʻau to perform a feeding role similar to that of woodpeckers, despite evolving in an environment where those birds are not found. Its unusual anatomy has long intrigued researchers. While scientists understood how the bird behaved when searching for food, the precise anatomical mechanisms that allowed it to drill into wood without injuring itself were less clear. The new research offers a closer look at how its body makes this specialised feeding technique possible.

THE SURPRISING ROLE OF ITS LEGS AND ANKLES One of the study's most striking findings concerns the bird's feet and ankle structure. Researchers discovered that the 'akiapōlāʻau has a proportionally large tendon associated with a muscle that flexes the ankle. This gives the bird the ability to generate a powerful downward movement when gouging into wood. Unlike woodpeckers, which primarily rely on their neck muscles when striking surfaces, the 'akiapōlāʻau uses the momentum of its entire body. Its movement begins with its legs and ankles, which help generate the force needed to drive its beak into a branch.

Lead author Alexander Clark, a PhD candidate at the University of Chicago and an affiliate of the Field Museum, compared the movement to swinging an axe to split a log. The bird raises its body and then drives itself downwards, using its legs as part of the striking mechanism. The researchers also identified other anatomical features that help explain its unusual feeding behaviour. These include a bony structure in the upper bill that is substantially shorter than the external bill itself, as well as proportionally shorter wings and a shorter thigh bone compared with mainland bird counterparts.

Some of these features resemble adaptations seen in unrelated woodpecker species, offering further insight into how different birds can evolve similar solutions to comparable ecological challenges. WHY DID THIS UNUSUAL BIRD EVOLVE IN HAWAII? The 'akiapōlāʻau's specialised anatomy is also a window into the evolutionary history of the Hawaiian islands. Hawaii is one of the world's most isolated island chains, and its native wildlife has evolved over long periods in relative isolation. With different species competing for limited food and habitats, unusual adaptations can emerge as animals find ways to occupy ecological niches that other species may not fill.

Researchers believe competition for food resources, including insects needed to feed young birds, may have contributed to the evolution of the 'akiapōlāʻau's distinctive feeding system. Co-author Paul Banko, a former researcher at the USGS Pacific Island Ecosystems Research Center in Hawaii, points to the emergence of new island habitats and the diversification of animal species as important parts of this evolutionary story. The bird is a striking example of how evolution can shape an animal's anatomy around a particular way of surviving. Its beak, legs and body mechanics have developed together to help it access food in a habitat where other specialised feeders are absent.

A REMARKABLE BIRD FACING THE THREAT OF EXTINCTION For all its extraordinary adaptations, the 'akiapōlāʻau faces a deeply uncertain future. Experts estimate that fewer than 2,000 individuals remain in the wild. The surviving population is restricted to the northeastern slope of a single mountain on Hawaii's Big Island, making the species particularly vulnerable to threats affecting its limited habitat. The bird is endemic to Hawaii, meaning it is found nowhere else in the world. Its survival is therefore closely tied to the health of the island's native ecosystems. Hawaii has some of the highest levels of species endemism, but this remarkable biodiversity comes with considerable vulnerability.

Isolation has allowed unique species to evolve, but it also means that many have limited options when their habitats or environmental conditions change. Native terrestrial wildlife across the Hawaiian archipelago has faced centuries of decline, with extinction pressures increasing in recent decades. The loss of an endemic species would mean more than the disappearance of a bird: it would erase a unique evolutionary history, including its behaviours and ecological role.