Huia are one of Aotearoa’s most well-known birds, despite going extinct over 100 years ago. Early European scientists were fascinated by the radically different bills of the male and female huia, a feature called sexual dimorphism. More recently scientists recognised the New Zealand wattlebird family, which includes huia, as one of three families worldwide containing the most extreme variation in bills. A new study by Massey University’s Gillian Gibb and Te Papa’s Lara Shepherd used DNA sequences to determine when the New Zealand wattlebird family and the extraordinary sexual dimorphism in huia evolved. Science Researcher Lara Shepherd discusses the findings.
A memorable museum experience
My first introduction to huia was as a teenager when I attended an exhibition on the species at the Te Manawa Museum in Palmerston North. The entire exhibition was fabulous but one part really resonated with me: the call of a huia. Huia went extinct around 1907 so this was not a recording of an actual huia call. Instead, it was an electronic re-creation, based on a recording of an imitation of huia calls by Hēnare Hāmana. It was a sobering moment when I realised that I would never have an opportunity to hear this haunting sound in the wild.
Perhaps this moment led me to later include huia in my PhD studies, where I attempted to determine the family tree of huia and its relatives using DNA. For my thesis, I confirmed that the members of the New Zealand wattlebird family (Callaeidae) – kōkako, tīeke (saddleback), and huia – are closely related. However, I could only retrieve short pieces of huia DNA, which did not contain enough information to indicate whether it was more closely related to kōkako or to tīeke.
New data indicates a recent origin
Fast-forward 17 years and new, more powerful DNA sequencing techniques have been developed. It is now possible to obtain huge amounts of DNA information, including from extinct species. Several studies have published numerous DNA sequences from kōkako, tīeke and huia but no one had done a comparison between them… until now.
My collaborator Gillian used her computer wizardry to combine and analyse the DNA sequences from several different studies. The results in our recently-published study clearly show tīeke and huia to be more closely related to each other than either were to kōkako.
Our molecular dating analysis indicates that kōkako diverged first, around 7 million years ago. Huia and tīeke separated from each other around 5 million years ago. At this time Aotearoa looked quite different from the present. The Southern Alps were only just starting to be uplifted and much of the southern North Island was underwater!
Other studies have shown that many of our other endemic birds also began to diverge into different species at around this time, including moa and the parrots kākā and kea. The similar timeframes indicate that the considerable bill variation within the wattlebird family, including the different bills of the male and female huia, is not a result of them having longer to evolve than other New Zealand birds.
A diet of insect larvae
A clue to why huia evolved sexual dimorphism in bill size and shape may come from their diet. Huia mostly ate insect larvae from rotting wood. Males chiselled into the wood and then opened their bills to wedge open the wood, whereas females probed the rotten wood with their long, curved bills.
Interestingly, sexual dimorphism in bill size and/or shape has also been observed in several unrelated bird families, although not to the extent seen in huia, indicating that this feature has evolved independently several times. Many of these species also feed on insect larvae in wood. It has been suggested that bill dimorphism has evolved to reduce competition between the sexes by allowing them to access different foods, such as grubs at different depths in rotten logs.
Huia are long extinct. But new technologies, such as genomics and isotopes, enable scientists to continue uncovering new information about their origins and lifestyle.
I doubt competition for food is a realistic hypothesis between pairs, and the difference in bill shapes between male and female huia is far from outlandish given males and females in many species adopt different behaviours and roles in partnership. Therefore it is quite reasonable to speculate that male huia bills are shorter and stouter than their female mates if their role was to punture through bark to provide access to grubs and larvae for mutual benefit.
actual fossils can be reasonably well dated, but their actual taxogenic origin can, or rather must, be much older. Hence, any estimation about their true origin must remain speculative, with or without molecules.
In addition the old notion, that the huia did evolve different bills in male and female in order to avoid food competition between sexes of the same species sound very outlandish as well.