Giant eagle: furious and yet vulture-like

With a wingspan of three meters, the Haaa eagle continued to hover over New Zealand until the 15th century: How did the largest eagle of all time, which the indigenous peoples still dated, feed themselves? It has apparently been specially adapted to large prey, such as the ratite Moa, which can weigh up to 200 kilograms, researchers say. The features of the skull and claws point to the Haast eagle as a deadly predator. But the other head features are more in line with scavenger vultures. The giant probably prefers to feed on the internal organs of its victims, the researchers explain.

In addition to fossil finds, rock carvings and Maori oral traditions testify to ancient giants in New Zealand’s skies. It is believed that the settlement of the islands by humans brought an end to the Haast eagle (Hieraaetus moorei): shortly after its arrival, it became extinct at the beginning of the 15th century. Presumably, it happened mainly indirectly through the extermination of its food base – the island’s large ratites. However, it was not clear for a long time whether the eagle killed the extinct moa itself or was rather a scavenger. However, previous research results have already spoken in favor of the hunter, and the Haaa eagle is also depicted as a rabid bird of prey in Maori traditions: it is said to even grab people.

How did the legendary giant feed himself?

To find out more about the mystery bird’s diet, an international research team led by Anneke van Heteren of the Munich State Zoological Collection looked again at its characteristics. The scientists explain that the way of life of birds of prey, such as eagles and vultures, is mirrored by the features of their skulls, beaks and claws. For their research, the scientists therefore recorded the shape and biomechanical properties of these body parts in the fossils of Haast’s eagles. They then compared the features with those of five live bird species and scavenger vulture species. They also developed computer simulations that provide clues as to the importance of each trait in killing and feeding.

As reported, it became clear that Haast’s eagle’s skull looked more like a vulture, while its beak and claws looked more like eagles. Detailed results showed that the bite of the New Zealand eagle was probably especially strong compared to the bite of other species of eagles. In addition to size, the claws of the Hieraaetus moorei were particularly impressive: their simulated shape change after capture showed that they could withstand extremely high loads. This confirms that Hieraaetus moorei, unlike other species of eagles, was adapted to the hunting of very large prey such as moa.

A mix of eagle and vulture traits

However, the giant eagle apparently ate its prey, which probably weighed up to 200 kilograms, like a vulture. This is due to the typical deformability characteristics of the skull, which make it easier to immerse the head in a dead animal, the researchers explain. Haast’s eagle’s skull features are most similar to those of the Andean condor. This vulture, in turn, is known mainly for devouring the guts of carcasses.

“Biometric analyzes of the claws and skull clearly show that Haast’s eagle killed a prey that was larger than it. Usually, however, only vultures feed on such large animals. On the other hand, eagles kill and eat little prey, ”van Heteren concludes. According to her, this causes a mixture of eagle-like and vulture-like traits in the haast eagle: “We suspect that he stuck his head deep into his victim’s intestines like a vulture to eat it” – explains the scientist.

As the researchers conclude, there is also evidence of another trait that fits this diet: Maori rock carvings on New Zealand’s South Island suggests that Haast’s eagle looked like a bald vulture.

Source: Bavarian State Collections of Life Sciences, Article: Proceedings of the Royal Society B: Biological Sciences, doi: 10.1098 / rspb.2021.1913

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