Aotearoa New Zealand has just two living species of honeyeaters, but they fit the mould. Tūī and bellbirds/korimako must be two of our loudest and most aggressive native birds, also among our most beautiful. Those of us who supply sugar water to these taonga in winter can attest to that!
Both species are endemic to Aotearoa, living nowhere else in the world. The raucous tūī (Prosthemadera novaeseelandiae) occurs throughout the country, from the Kermadec Islands/ Rangitāhua to the Auckland Islands/Mōtū Maha and the Chatham Islands/Rēkohu.
Tūī are generally less common in the South Island, but my personal observation is that Dunedin populations have boomed over the past 30 years. They are returning, too, to areas of Canterbury from which they had disappeared decades ago. Their glossy plumage and adorable white bobble are well known, not just to trampers but also to people in cities and towns across the motu.
The melodious green bellbird (Anthornis melanura) has a more southerly distribution. It lives from the Three Kings Islands/Manawatāhi to the Auckland Islands, but has been absent from Northland for many years, possibly as a result of disease. Recent conservation efforts have seen the gradual return of korimako song to parts of Northland.
What has been less clear, however, are the details of honeyeaters’ evolutionary history. The molecular tools of modern genetics have recently revealed several surprises.
First, we used to think we had three native honeyeater species. But the stitchbird/hīhī, which scientists call Notiomystis cincta, is not a honeyeater. It turns out to belong to its own endemic family, the Notiomystidae (a story for a different column).
Second, it turns out we did have three species after all. The family tree (see diagram) shows a story all too familiar in our country: we have lost a species to extinction.
The Chatham Islands bellbird/kōmako was indeed a distinct species, A. melanocephala, not just a regional variant or subspecies. Its ancestors diverged from the mainland species a little under 2 million years ago.
Third, as a result of this extinction, tūī and korimako are now each other’s closest relatives, although they have been on their own separate evolutionary pathways for about 5 million years.
Sister species, as such pairs are known, usually look rather similar, just as closely related people do. But I think these two species do not look alike at all, although their songs are easily confused.
Fourth, the closest relatives of our New Zealand species are not found, as one might expect, in the nearest parts of Australia. Indeed, the next of kin are two species of honeyeater from forested parts of New Guinea (the plain and marbled honeyeaters) and one from inland desert regions of Australia (the pied honeyeater).
Just how this South-Pacific relationship arose is not clear. But it is worth noting that the divergence of the New Zealand and Austro-Papuan lineages occurred about 15 million years ago. That is plenty of time for significant changes in plumage, size, behaviour and habitat preference to have evolved, and for Aotearoa New Zealand to have acquired her own special honeyeaters.
Hamish G. Spencer is emeritus professor in the Department of Zoology at the University of Otago. Each week in this column, writers address issues of sustainability.
