New Zealand's Haast's Eagle, the largest in the world, may have been bald and a carnivorous predator, according to new international research.
A team of researchers compared the skull, beak and talons of the eagle to those of five living meat-eating birds to learn about its feeding habits.
Since Haast's Eagle or Pouākai was formally described by Julius von Haast in 1872, scientists have debated whether it was a predator or a scavenger.
Canterbury Museum natural history senior curator Paul Scofield, who was one of the researchers, said it had become clear the eagle was a predator, not a scavenger.
Its talons were found to be similar to those of today's eagles, although they were much larger and more powerful.
These similarities suggest that the Haast's Eagle used its talons to hunt.
"As a result of this research, when we picture a Haast's Eagle feeding we can imagine them swooping down on a moa, grabbing on with those huge talons and using its powerful beak to deliver the killing blow," Dr Scofield said.
While the bird's beak and talons were eagle-like, the shape of its neurocranium - the section of skull that encloses the brain, and a key indicator of feeding behaviour in birds - was most like that of the Andean condor, a South American vulture.
Most eagles hunt prey that is smaller than them, apart from condors.
Dr Scofield said the research suggested this was the case with Haast's Eagle too.
"Haast's Eagle was going after moa that could weigh up to 200kg - more than 13 times their own body weight," Dr Scofield said.
"Condors also often eat animals that are much larger than them, so it makes sense that they'd have similar feeding habits."
The condor is also gulper, a bird that feeds on the soft internal organs of a carcass, and it is thought Haast's Eagle was as well.
"Once the moa [or other prey] was down, the eagle would go straight for the back of the skull and for the guts and other soft organs," Dr Scofield said.
It could also mean its head and neck might also have been featherless like that of the condor and most other vultures.
The theory is supported by a Māori drawing at Craigmore Station in South Canterbury, which shows the head and neck of the bird uncoloured.
The new research was published today in the peer-reviewed journal Proceedings of the Royal Society B.