New Zealand was once home to the largest eagle in the world, Harpagornis moorei, often known as Haast’s eagle. I’m not a fan of that name: Julius von Haast was the Director of the Canterbury Museum and the first to scientifically describe the eagle, from bones collected from a North Canterbury swamp, in 1871. But getting an eagle named after yourself seems a trifle vain, so I prefer to call it the New Zealand eagle or the giant eagle, both of which are more descriptive.
Harpagornis is a marvellous name: “grappling-hook bird”, for its enormous clawed feet. What its Māori name was we’re not sure: pouakai and hokioi have both been recorded, but by the time written transcripts were being made the eagle had been extinct for centuries and had entered the realm of legend.
Recent examination of its DNA shows that the New Zealand eagle was most closely related to the Australian little eagle (Hieraaetus morphnoides), the smallest eagle on that continent. Its ancestors were blown to New Zealand and increased in size tenfold within a million years, an extraordinarily-rapid increase. Giant eagles weighed about 10kg in males and 14kg in females, nearly half as large again as the largest eagles alive today. They were big enough to kill adult moa—we’ve found the claw marks in moa pelvic bones. And they would have been very capable of killing humans too, which is probably why they were wiped out quite quickly, along with moa, soon after Polynesians arrived in New Zealand.
One account of the eagle, collected by Sir George Grey from a Ngāti Apa elder around 1850, describes it as living in the mountains, having red, black, and white feathers with a red crest, and being as big as a moa. The problem with this account is that giant eagles never, as far as we know, lived anywhere near Ngāti Apa in the Whanganui or Manawatu area. All the fossils we’ve found are from the eastern South Island and Southern Alps. So this centuries-old tradition is unlikely to be based on eye-witness accounts.
Older reconstructions of the giant eagle, based on this 19th century description, show it with lurid red plumage and a pointed crest. Its closest relative, the little eagle, is a rather more inconspicuous rusty brown. Most recent depictions give it the brown plumage of an Australian wedge-tailed eagle. Almost none of the reconstructions, however, get the head right: the giant eagle had an extraordinarily long skull, half as long again as you’d expect from a bird its size. The recent David Attenborough documentary set inside the Natural History Museum included a computer-animated Harpagornis, but it was really just a scaled-up golden eagle, with long narrow wings and a too-short skull.
(Attenborough was rather guilty of exaggeration when he described the eagle, in breathless voice-over, as having “a beak the size of a butcher’s cleaver”. Its beak is actually about 7 cm long, the size of my little finger or a paring knife.)
The giant eagle’s extremely long bill, with small bony flaps protecting the nostrils, is actually rather like that of some species of Old World vultures. A vulture’s elongated bill is an adaptation for sticking its head inside the messy carcasses of animals much larger than itself. Most eagles don’t need such bills, because they’re feeding on relatively small prey. But giant eagles were killing moa 15 times their size, so their feeding would have been similarly messy. Not only did they have the elongated beaks of vultures, they perhaps had the short head feathers or even bald heads of them as well.
Ornithologists who study the New Zealand eagle get defensive when you suggest it may have had a head like a vulture. For decades, Harpagornis was victim of a terrible slander: its short wings supposedly meant it was on its way to becoming flightless, and it thus must have spent most of its time on the ground scavenging moa carcasses. In fact, short wings are a characteristic of forest eagles that need to maneouver around trees, not soar for long distances. And the discovery of claw marks on moa bones show that Harpagornis was indeed killing its own prey. But it took quite some time to dislodge its reputation as a scavenger, and a vulture-like reconstruction would hardly help.
Whether the New Zealand eagle had a bare head, or indeed a fancy red crest, is ultimately something we can’t determine from the few remaining bones. Māori rock art depictions of eagles are too stylised to help. Nobody has seen one for 500 years. Perhaps one day a mummified skull with feathers will turn up, as has happened with moa. But ultimately we have to make our own estimate of what’s probable, and rexognise that all depictions of a long-extinct creature, however convincing, are mostly well-informed guesses.
Dr Mike Dickison is Curator of Natural History at the Whanganui Regional Museum.