Sarothrura

The Mysterious Adzebill

New Zealand was once home to many flightless birds. Some, like the moa, are well-known, but others, like our flightless ducks, geese, and owlet-nightjar, are familiar mostly to palaeontologists. One bird that deserves to be better known is the mysterious adzebill.

1. Adzebill Martinson

A North Island adzebill (Aptornis otidiformis) eyes up a tuatara in a 2005 painting by Paul Martinson.
Photo: Te Papa / CC-BY-NC-ND

There were two species of adzebills, Aptornis otidiformis in the North Island and Aptornis defossor in the South. Both were huge. When their bones were first discovered, they were mistaken for a small moa. Fully-grown birds would have weighed perhaps 20 kg, larger than a swan or pelican.

Adzebills had massive heads with heavy down-curved beaks. The beaks tapered to a point, and Dr Richard Holdaway, who coined the name “adzebill”, once confessed to me that “pick-bill” would have been more accurate. The robust vertebrae in their neck would have anchored strong muscles and allowed them to deliver a powerful blow.

These birds also had massive feet, with strong tendons, that would have made them good at digging. For some time biologists debated what they ate. Did they dig up roots, pluck leaves or break apart rotten logs? Their beak wasn’t hooked like a bird of prey.

A technique called stable isotope analysis which lets us analyse animals from the composition of bone – you are what you eat – revealed that adzebills were carnivores. We can imagine them tearing open trees for huhu grubs, plucking lizards or baby birds off the forest floor, digging up giant earthworms, and excavating tuatara, or even nesting seabirds, out of their burrows.

A second mystery was what adzebills were, exactly. They didn’t resemble rails like the weka or takahē, and for some time were put in their very own family. Some ornithologists thought their closest relative was the flightless kagu of New Caledonia. Others thought it belonged with chicken-like South American birds called trumpeters. The debate continued fruitlessly for decades.

Alex Boast is a PhD candidate at the University of Auckland, working on ancient DNA. Improved techniques now allow us to recover and examine fragments of DNA from bones and eggshell of extinct birds, not enough for Jurassic Park cloning, but enough to construct a family tree and determine their nearest relatives. Alex analysed adzebill DNA and compared them to numerous other birds, and the results suggest that adzebills are not kagus, or trumpeters. They are flufftails.

2. Flufftail Keugelmans

The white-spotted flufftail (Sarothrura pulchra), painted by John Keulemans in 1894. This delicate little bird seems to be the adzebill’s closest living relative.
Ref: Wikimedia Commons

Flufftails (nine species in the genus Sarothrura) are secretive ground-dwelling birds about the size of a starling, rusty brown and spotted. They do indeed have fluffy tails. What’s unusual is that flufftails are all found in Africa, and on the island of Madagascar, nowhere near New Zealand.

Africa and New Zealand were once connected as part of the supercontinent Gondwana of course, and fossils tell us that adzebills have been here for millions of years, plenty of time for their ancestors to get here and evolve into a giant flightless predator. Intriguingly, the kiwi seems to have done the same thing. Its closest relative is another African species, the elephant bird of Madagascar. The difference is, while one flightless bird survived the arrival of human beings and became the symbol of New Zealand, the other was wiped out. The not-so-mysterious adzebill is now mostly forgotten.

 

Dr Mike Dickison is curator of natural history at the Whanganui Regional Museum.

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