Hawaiian Bird Uses Ankle Tendon to Drill for Insects
Research involving the Field Museum reveals that the 'akiapōlāʻau relies on full-body mechanics rather than neck strength to bore into wood.
By Aaron Foster ·
A new study clarifies the physical mechanics behind the foraging behavior of the endangered 'akiapōlāʻau.
Researchers led by University of Chicago Ph.D. candidate Alexander Clark determined that the bird uses a large tendon in its ankle to generate the force needed to drill into branches.
The 'akiapōlāʻau, or Aki, possesses a specialized bill described as a "Swiss Army beak." The upper mandible is long, narrow, and flexible, allowing the bird to probe nooks and holes for grubs and caterpillars. The lower mandible is short and broad, functioning as a tool for boring into wood.
Previous observations confirmed the bird's actions but not the anatomical source of its power. Clark noted that scientists knew what the birds were doing but not how their bodies facilitated the movements without injury.
The new findings indicate that the Aki swings its entire body downward quickly and forcefully. This motion is compared to swinging an axe. The bird anchors itself against the tree while bending its ankles upward to initiate the strike.
This mechanism differs from woodpeckers, which rely primarily on neck muscles for similar tasks. Woodpeckers are not native to the Hawaiian Islands.
Paul Banko, a co-author and former researcher at the USGS Pacific Island Ecosystems Research Center, said the evolution of this specialized tool suggests intense ecosystem competition. He stated that when Oahu emerged from the water, a large explosion of animal species occurred. This diversity likely drove competition for resources like caterpillars to feed young birds.
Experts estimate fewer than 2,000 Aki remain in the wild. The species is found exclusively on the northeastern slope of one mountain in Hawaii.
