Giant eagle ruled New Zealand skies

A new study shows that New Zealand's giant – and now extinct – Haast's eagle ruled the skies until 500 years ago, swooping down on moa.

Scientists have known about the existence of Haast's eagle since 1871 based on excavated bones, including bones carved by early Maori, but their behaviour was not entirely clear.

Because of their large size – they weighed up to 18kg with wingspans up to 3m – some scientists believed they were scavengers rather than predators.

Earlier research has indicated the eagle had enough strength in its talons to kill a moa weighing 180kg, attacking at up to 80kph, or even to attack a human child.

The latest study throwing new light on this was published in the Journal of Vertebrate Paleontology.

Researchers Dr Paul Scofield, curator of vertebrates at the Canterbury Museum, and Professor Ken Ashwell of the University of New South Wales used computerised CT and CAT scans to reconstruct the size of the brain, eyes, ears and spinal cord of the Haast's eagle.

These details were compared to values from modern predatory and scavenging birds to determine the habits of the extinct eagle.

"This work is a great example of how rapidly evolving medical techniques and equipment can be used to solve ancient mysteries," said Dr Ashwell.

But the latest study showed that not only was Haast's eagle a fearsome predator that probably swooped on its prey from a high perch, it also it evolved over a relatively short period of time from a much smaller-bodied ancestor.

This is similar to findings by Michael Bunce, of Oxford University, in 2005, which showed it underwent a rapid evolutionary transformation and was originally related to some of the world's smallest eagle species two million years earlier. It is the only eagle known to have been the top predator in an ecosystem on land.

The eagles are thought to have struck their prey from the side, tearing into the pelvic flesh and gripping the bone with claws the size of a tiger's paw, so that the moa could be killed by a single strike to the head or neck from the eagle's other claw.

The new research is also an example of how the oral traditions of ancient peoples and scientific research can sometimes reach the same conclusion, said Dr Scofield, the lead author on the project.

"This science supports Maori mythology of the legendary pouakai or hokioi, a huge bird that could swoop down on people in the mountains and was capable of killing a small child," he said.

Haast's eagle became extinct a mere 500 years ago, probably due to habitat destruction and the extinction of moa by early Maori, who are thought to have arrived in New Zealand, about 1280.

Dr Scofield has previously said that people living on the Wairau Bar around 1300AD co-existed with the eagle.