Cave paintings in New Zealand’s South Island depict the majestic bird known as Te Pouākai, or Te Hōkioi.
• Haast’s eagle lived on New Zealand’s South Island until around 500 years ago
• While it had the talons and beak of an eagle, it had the head of a vulture so it was unclear whether it was mainly a hunter or scavenger
• A study reveals it killed like an eagle, but had the table manners of a vulture
According to Māori legend, the bird, thought to be Haast’s eagle (Hieraaetus moorei), could swoop down and carry off adults and children.
Weighing up to 18 kilograms, or around three times as much as the wedge-tailed eagle, and with a 3-metre wingspan, it was the largest eagle that has ever lived.
While it had the talons and beak of an eagle, it had the head of a vulture, leading some people to speculate it might have been more of a scavenger than a hunter.
But either way, the bird was worthy of its fearsome reputation, according to a new study.
While it used its tiger-claw-sized talons to kill, it had the table manners of a vulture, with a skull designed to dive deep into the juicer parts of its catch, the analysis published in Proceedings of the Royal Society B found.
“This was undoubtedly the biggest, baddest eagle ever,” said zoologist and study co-author Steve Wroe of the University of New England.
“It couldn’t have picked you up and carried you away, unless you were a child perhaps, but there’s not much doubt it could have got its talons into your brain.”
A quirk of rapid evolution on island
The bird’s curious mix of features is likely to have developed as a result of its rapid evolution.
The closest relative of Haast’s eagle today is the Australian little eagle (Hieraaetus morphnoides).
“[Haast’s eagle] evidently blew in from Australia sometime within the last 1 to 2 million years, then very rapidly evolved to be a giant,” Professor Wroe said.
“It’s probably the most extreme example of rapid evolution in size that we know of in any vertebrate.
“It’s basically gone from being a 1-kilo bird to an 18kg bird.”
Landing on an island with no predators, it quickly evolved features and behaviours that allowed it to rule the roost.
Until humans arrived in Aotearoa in the 13th century, the giant eagle feasted on moa, a hefty flightless bird that weighed up to 200 kilograms.
To see how it was possible to take down such a big bounty, the international team built 3D computer models of the eagle’s skull and talons and simulated feeding and killing behaviours to compare its performance with that of living eagles and vultures.
The analysis showed the bird’s talons could easily withstand high loads and take down prey much bigger than itself.
“Birds of prey rarely try to kill things bigger than themselves,” Professor Wroe said.
“Any time you get in there and wrestle with anything bigger than yourself, you risk breaking a wing, which is almost invariably fatal for a bird.”
Taking down a moa would have been risky.
“A 200kg bird would have had a hell of a kick on it,” Professor Wroe said.
But it was a risk that could have paid off without any competitors, except for other eagles, to steal its food.
“If it took out a moa, it’s got food for itself and its family for days.”
Rather than tearing flesh by gripping it with its beak and shaking it side to side like an eagle, the bird’s skull was designed to rip and pull flesh from deep inside a carcass like a vulture.
An image of the bird in the Cave of the Eagle on New Zealand’s South Island also tied in with the hypothesis that the eagle had a vulture-like head.
“It’s a very dark body but … the head appears to be bald,” Professor Wroe said.
“Vultures almost universally have bald heads, and it’s almost certainly so they don’t accumulate too much blood and guts in the feathers on their head, which are very hard to clean.”
Despite its appearance though, Professor Wroe said the bird was still very much an eagle.
“It’s an example of convergence, which is where two unrelated animals converge with respect to morphology because they’ve got similar habits.”
Battle of the big birds
Haast’s eagle was probably both a killer and a scavenger, said palaeontologist Trevor Worthy of Flinders University, who was not involved in the study.
“Like most other birds of New Zealand, they became generalists and not very specialised, so they were able to take on multiple roles,” Dr Worthy said.
“It could quite happily dispense with a very large animal, but it could fly around and look for a dead one and eat that.”
There is no doubt it took down moa with its talons, he said.
“I’ve looked at moa pelvises where you can line up great rips in the bones.
“Those claws were powerful to cut through the feathers and skin, then 5 centimetres of flesh, then 5 millimetres of the pelvis.
“Under that pelvis is the kidney, so once you start ripping that up, you die pretty quickly,” he said.
But, Dr Worthy said, adult moa was unlikely to be the eagle’s primary source of food.
“The moas we’ve seen that have been killed were already mired in a swamp, so they couldn’t actually run anywhere.
“If a young moa was walking across a clearing, then the eagle could swoop down and get it, but it probably wouldn’t tackle an adult moa.
“In reality, eagles are in the swamps too, which means they actually got killed in the process of dealing with a moa.”
In the end, neither the eagle nor the moa were a match for humans.
Both birds became extinct around 500 years ago.
abc.net.au, 1 December 2021