With a wingspan of three meters, the Haastadler circled over New Zealand until the 15th century: How did this largest eagle of all time, which the indigenous people still met, feed on? Apparently it was specially adapted to large prey such as the moa ratites, which can weigh up to 200 kilograms, researchers report. Features of its skull and claws show the Haastadler as a deadly predator. But other features of the head are more appropriate for scavenging vultures. Presumably, the giant preferred to feed on the internal organs of its victims, explain the researchers.
In addition to fossil finds, rock carvings and oral traditions by the Maoris also bear witness to the former giants in New Zealand’s skies. It is assumed that the human settlement of the island world brought the end of the Haastadler (Hieraaetus moorei): soon after their arrival it died out in the early 15th century. Presumably this happened mainly indirectly through the extermination of its food source – the island’s large ratites. For a long time, however, it remained unclear whether the eagle killed the extinct moas itself or whether it was more of a scavenger. Earlier research results, however, already spoke in favor of a hunter and the Maori tradition also portrays the Haastadler as a rabid bird of prey: It is said to have even preyed on people.
How did the legendary giant feed?
In order to find out more about the diet of the mysterious bird, an international research team led by Anneke van Heteren from the Zoological State Collection in Munich has now looked again at its characteristics. As the scientists explain, the way of life of birds of prey such as eagles or vultures is reflected in features of their skulls, beaks, and claws. For their study, the scientists therefore recorded the shape and biomechanical properties of these body parts in the fossils of Haastadler. They then compared the characteristics with those of five birds of prey and scavenger vultures living today. They also developed computer simulations that provide clues as to the importance of the respective characteristics in killing and eating.
As they report, it became clear that the skull of the Haastadler was shaped more like a vulture, while the beak and claws were more like those of eagles. The detailed results showed that the New Zealander’s bite was probably particularly powerful compared to that of the other eagle species. The claws of Hieraaetus moorei were also particularly impressive, apart from their size: Their simulated change in shape when grabbed showed that they could withstand extremely high loads. This confirms that Hieraaetus moorei, in contrast to the other eagle species, was adapted to the killing of very large prey such as the moas.
Mixture of eagle and vulture traits
The giant eagle then apparently ate its victims, presumably weighing up to 200 kilograms, like a vulture. This is evident from the typical characteristics of the deformability of the skull, which make it easier for the head to be immersed in a dead animal, the researchers explain. The characteristics of the Haastadler skull are most similar to those of the Andean condor. This vulture, in turn, is known for devouring mainly the bowels of carcasses.
“The biometric analyzes of the claws and skull make it clear that the Haastadler hunted prey that was larger than itself. Usually, however, only vultures feed on such large animals. Eagles, on the other hand, tend to kill and eat small prey, ”concludes van Heteren. According to her, this results in the mixture of eagle and vulture-like characteristics in the Haastadler: “We suspect that it stuck its head like a vulture deep into the bowels of its prey in order to eat it,” explains the scientist.
As the researchers conclude, there is also evidence of another trait that goes with this diet: A Maori rock drawing on New Zealand’s South Island suggests that the long-haired eagle looked like a bald vulture.
Source: State Natural Science Collections of Bavaria, specialist article: Proceedings of the Royal Society B: Biological Sciences, doi: 10.1098 / rspb.2021.1913