The Oʻahu ʻAmakihi: A Glimpse into its Biology, Endemism, Evolutionary History, and Phylogeny

Radd Icenoggle

December 27, 2023

Birding,Evolution & Phylogenetics,Hawaii 2023

Two shots…I got just two shots of an Oʻahu ʻAmakihi (Chlorodrepanis flava), and two photos were enough to scratch my Hawaiian endemic itch. Endemic to the island of Oahu (particularly, the wetter southern area of Oʻahu. Endemism refers to the phenomenon where a species is found exclusively in a particular geographic location, and this isolation can play a pivotal role in evolving unique characteristics. This small, vibrantly colored bird offers a fascinating glimpse into endemism, evolutionary history, and phylogeny.

The Oʻahu ʻAmakih is a striking bird with vibrant yellow and green plumage, adorned with subtle streaks of gray. Typically ranging from 4 to 5 inches in length, these tiny birds are known for their slender, slightly curved bills that are perfectly adapted for extracting nectar from flowers, particularly the ʻōhiʻa lehua (Metrosideros polymorpha). This mutual relationship formed in a delicate dance of co-evolution between the ʻAmakihi and the flora they rely on for sustenance.

Oahu, a pivotal island in the Hawaiian archipelago, likely played a crucial role in shaping the diverse morphologies observed among honeycreepers. The island’s formation facilitated cycles of colonization and speciation between Kauai and Oahu, contributing to the unique evolutionary tapestry of Chlorodrepanis flava and its fellow honeycreepers.

Hawaiian honeycreepers are characterized by highly distinctive morphologies and are believed to have originated in the mid-late Pliocene, after the formation of Oahu but before the formation of Maui.

Before the advent of molecular phylogenetic techniques, the classification of Hawaiian honeycreepers, including Chlorodrepanis flava, was a subject of controversy. Some authorities categorized them as a distinct family, Drepanididae, while others considered them a subfamily, Drepanidinae, within the finch family Fringillidae. Recently, the entire group has been incorporated into the finch subfamily Carduelinae.

Chlorodrepanis flava, the Oʻahu ʻAmakihi, and other Hawaiian honeycreepers are now recognized as the sister taxon to Carpodacus. Their ancestors are believed to have originated in Asia, diverging from Carpodacus approximately 7.2 million years ago. The migration to and radiation on the Hawaiian Islands occurred between 5.7-7.2 million years ago, coinciding with the formation of Ni’ihau and Kauai.