The legend of giant eagles
4 January 2005
Gigantic eagles swooping from the skies to rescue Frodo and Sam in Peter Jackson's Tolkein inspired film trilogy "Lord of the Rings" may not be just the stuff of legends and fairytales, according to research published today in the journal 'PLoS Biology'.
Scientists from the University of Oxford in the UK and the University of Canterbury in New Zealand have shed new light on the evolution of the extinct giant eagle that once ruled the skies over New Zealand.
The enormous Haast's Eagle dominated its environment. Weighing in at 10–14kg, it was 30–40% heavier than the largest living bird of prey around today, the Harpy Eagle of central and south America, and was approaching the upper weight limit for powered flight.
Led by Professor Alan Cooper from Oxford University's Ancient Biomolecules Centre, the New Zealand researchers extracted DNA from fossil eagle bones dating back about 2000 years.
Dr Michael Bunce, who carried out the research, said, "When we began the project it was to prove the relationship of the extinct Haast's Eagle with the large Australian Wedge-tailed Eagle. But the DNA results were so radical that, at first, we questioned their authenticity."
The results showed that the New Zealand giant was in fact related to one of the world's smallest eagles – the Little Eagle from Australia and New Guinea, which typically weighs under 1kg.
"Even more striking was how closely related genetically the two species were. We estimate that their common ancestor lived less than a million years ago. It means that an eagle arrived in New Zealand and increased in weight by 10–15 times over this period, which is very fast in evolutionary terms. Such rapid size change is unprecedented in birds and animals," added Dr Bunce.
Palaeobiologist Dr Richard Holdaway from the University of Canterbury in Christchurch, NZ, speculated on the reasons why Haast's Eagle grew so quickly to such vast proportions. "The size of available prey and the absence of other predators are, we think, the key factors driving the size increase. The eagles would have been able to feed unhindered on their kill."
Haast's Eagle is the only eagle known to have been the top predator in a major terrestrial ecosystem. They hunted moa, the herbivorous, flightless birds of New Zealand, which can weigh up to 200kg. With a truncated wingspan of around three metres, for flying under the forest canopy, the eagles struck their prey from the side, tearing into the pelvic flesh and gripping the bone with claws the size of a tiger's paw. Once caught, the moa would be killed by a single strike to the head or neck from the eagle's other claw.
The scientists believe the eagle died out within two centuries of human settlement of New Zealand. Forest fires destroyed its habitat and humans exterminated its food supply. There is some evidence to suggest the eagles were hunted too.
Before human settlement, 700 years ago, New Zealand had virtually no terrestrial mammals. Apart from bats, the only inhabitants were about 250 species of bird.
The eagle is thought to be the mythical giant "Hokioi" of Maori history and is recorded in rock art and artefacts shaped from eagle bones, proving that it co-existed with early Polynesians. There is, however, no evidence that man was ever a target for the huge predator.
Dr Holdaway went on to say, "There are so many unanswered questions about our biological past that ancient DNA can help provide answers to, and it's great to see New Zealand's birds being the focus of this international research."
Other research currently underway involves the DNA from ancient moa droppings and from soil in former petrel breeding colonies.
Dr Michael Bunce
Mob: (New Zealand) 027 44 77 322
Dr Richard Holdaway
University of Canterbury
Tel: +64 3 3493 455
Mob: +64 0274 513464
NERC Press Office
Natural Environment Research Council
Polaris House, North Star Avenue
Swindon, SN2 1EU
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1. The research was funded primarily by the Natural Environment Research Council. NERC is one of the UK's research councils. It uses a budget of about £300m a year to fund and carry out impartial scientific research in the sciences of the environment. NERC trains the next generation of independent environmental scientists.
Additional support was provided by the Wellcome Trust, the Leverhulme Trust and the Foundation for Research Science and Technology New Zealand.
2. The full article relating to this research is available on the PLoS Biology website. PLoS Biology is a peer-reviewed, open-access journal published by the Public Library of Science.
3. An illustration of a Haast's Eagle hunting moa is available as a TIFF. Contact Dr Michael Bunce, McMaster University, Canada or the NERC press office if you would like a copy.
If used, the illustration should carry the following acknowledgement - 'Image courtesy of John Megahan'.
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