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For more than a century, scientists have wondered whether a huge carnivorous bird that went extinct around 600 years ago was more of a predatory eagle or a gut-raiding vulture. Now we finally have the answer: it was both.

The Haast’s eagle, which lived in New Zealand, used its massive talons to hunt and capture prey like an eagle. But instead of gobbling it down whole like modern-day raptors, it ripped the animal’s belly apart and tore out its intestines – the “nicest bits”, says at the Bavarian State Collection of Zoology in Munich, Germany.

“It’s still actively hunting because it’s pulling down such huge prey, but then the feeding is much more of a pulling, like the way a vulture would on an elephant carcass, rather than the way an eagle would gulp down its prey in two or three bites,” says van Heteren.

The Haast’s eagle (Hieraaetus moorei) weighed up to 15 kilograms, about a third heavier than the largest living eagle, the harpy eagle (Harpia harpyja).

Ů��С��Ƶs have long suspected that the bird’s preferred prey was another bird, the land-roaming and now extinct moa, which could weigh up to 200 kilograms.

To answer the question of whether the Haast’s eagle fed more like a vulture or a true eagle, van Heteren and her colleagues created digital 3D models of preserved specimens of its skull and talons. They then compared those to the morphology of five other species of modern eagles and vultures.

With the help of computerised modelling, the researchers determined that, contrary to the conclusions of earlier scientific studies, the Haast’s beak is actually far more similar to that of other eagles than to carrion feeders. Haast’s eagles could have used their powerful bite to kill large prey such as moas. Their large talons also showed remarkable similarities to modern eagles, meaning they were well suited for capturing live prey, even animals far larger and heavier than themselves.

But that doesn’t mean it behaved entirely like an eagle, either, says van Heteren. Its neurocranium – the back upper part of the skull – is reminiscent of vultures. The modelling suggests it could bear strains similar to those of the Andean condor (Vultur gryphus), a South American vulture that gulps down internal organs.

“I thought we were going to get a clear-cut answer, and that that we would find either the one or the other,” says van Heteren. “But instead, we found a puzzle. The fact that [this bird] was hunting like an eagle and then eating like a scavenger surprised me.”

The discovery may, however, be consistent with ancient Maori rock art. At a site called the Cave of the Eagle at Craigmore Station, South Island, there is a depiction of a bird that is thought to be the Haast’s eagle. The bird has a coloured body but colourless head and neck, consistent with the idea that the Haast’s eagle might have been vulture-like, with few feathers on its head.

After consuming the internal organs – which are rich with nutrients – and perhaps the muscles, the raptors probably abandoned less appealing tissues such as the skin, bones and tendons, says van Heteren.

A lack of competition meant they could afford to be picky. “When you’re the king of the jungle, basically, you can just eat the nice bits and then move on and catch another one,” says van Heteren.

The Haast’s eagle went extinct in about AD 1400, after people arrived on the islands and hunted the moa to extinction.