Saturday - October 01, 2011

One For The Birds

Maori legend of man-eating bird is true
Creature that features in New Zealand folklore really existed, scientists say

A Maori legend about a giant, man-eating bird has been confirmed by scientists. Te Hokioi was a huge black-and-white predator with a red crest and yellow-green tinged wingtips, in an account given to Sir George Gray, an early governor of New Zealand. It was said to be named after its cry and to have “raced the hawk to the heavens”. Scientists now think the stories handed down by word of mouth and depicted in rock drawings refer to Haast’s eagle, a raptor that became extinct just 500 years ago, shows their study in The Journal of Vertebrate Paleontology.

Haast’s eagle (Harpagornis moorei) was discovered in swamp deposits by Sir Julius von Haast in the 1870s. But it was at first thought to be a scavenger because its bill was similar to a vulture’s with hoods over its nostrils to stop flesh blocking its air passages as it rooted around inside carcasses.

But a re-examination of skeletons using modern technology, including CAT scans, by researchers at Canterbury Museum in Christchurch and the University of New South Wales in Australia showed it had a strong enough pelvis to support a killing blow as it dived at speeds of up to 80kph.

With a wingspan of up to three metres and weighing 18kg, the female was twice as big as the largest living eagle, the Steller’s sea eagle. And the bird’s talons were as big as a tiger’s claws. “It was certainly capable of swooping down and taking a child,” said Paul Scofield, the curator of vertebrate zoology at the Canterbury Museum. “They had the ability to not only strike with their talons but to close the talons and put them through quite solid objects such as a pelvis. It was designed as a killing machine.”

Its main prey would have been moa, flightless birds which grew to as much as 250kg and 2.5 metres tall. “In some fossil sites, moa bones have been found with signs of eagle predation,” Dr Scofield said.

New Zealand has no native land mammals because it became isolated from other continents in the Cretaceous, more than 65 million years ago. As a result, birds filled niches usually populated by large mammals such as deer and cattle. “Haast’s eagle wasn’t just the equivalent of a giant predatory bird,” said Dr Scofield. “It was the equivalent of a lion.”

In a blink of geologic time an eagle the weight of a squirrel evolved into a giant predator that fed on animals twice as big as humans. It grew so large it approached the physical limits of flight, a new study suggests. Before man arrived in New Zealand 700 years ago the land was dominated by birds. With no land mammals, the more than 250 avian species created an isolated and unique ecology.

Amidst this remote laboratory the Haast’s eagle was 40 percent larger than today’s record holder, the Harpy eagle, and topped the local food chain. The eagle fed largely on the moa, an extinct flightless bird somewhat like an ostrich. Bones from moa as large as 440 pounds (200 kilograms) bear the marks of the Haast’s talons. The eagle held its victim by its pelvis and killed it with a strike to the throat or head, researchers say.

In the new study, scientists examined DNA from 2,000-year-old fossilized bones of a Haast’s eagle and compared it to older specimens that at first glance seem utterly unrelated.

The Haast’s ancestors, it turns out, were the little eagle and the booted eagle. They were only about 2.2 pounds (1 kilogram) when they crossed the waters from Australia to New Zealand. Within about a million years the predators evolved to as much as 33 pounds (15 kilograms) with a wing span of almost 10 feet (3 meters). For comparison, larger bald eagles today are close to 14 pounds (6.4 kilograms) and have a wing span around 6 feet (1.8 meters).

“We estimate that their common ancestor lived less than a million years ago. It means an eagle arrived in New Zealand and increased in weight by 10-15 times over this period,” Michael Bunce of McMaster University in Canada said Monday. “Such rapid size change is unprecedented in terrestrial vertebrates.”

Richard N. Holdaway, an extinction biologist and another member of the research team, explained that when the first ancestor of the Haast’s eagle arrived in New Zealand there was no competition for big meals like the moa. The larger the eagle the more offspring it could support because food was abundant if you were big enough to kill it. This became an avenue for survival that the once-small eagle employed to become sizeable quickly.

“With the largest individuals that could kill the largest prey being most successful at producing young, which themselves would be large birds by inheritance from their parents, the change in size within the species was probably rapid in geological time,” Holdaway told LiveScience.

The eagles grew so large in fact that they butted up against the limits of how much weight a bird can carry into the air.

“There is a body mass above which normal flapping flight becomes physically impossible,” said Holdaway, “Various studies have suggested that that occurs at a body mass of about 15 kilograms,” which is the estimated weight of the Haast’s eagle.

The Haast’s Eagle had relatively small wings for a bird with this body size, up to about 10 feet, making it less suited to endless soaring and better at living in the forests that covered the islands at that time.

Posted by Drew458     on 10/01/2011 at 12:44 PM   
Filed Under: • Animals •  
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