By Richard Gray, Science Correspondent
As souvenirs go, the giant fossilised egg that Sir David Attenborough keeps wrapped up for safe-keeping in the cellar of his London home is not bad for someone with a 60 year career as Britain's foremost natural history documentary maker.
Now in a bid to find out more about the foot long egg he collected on the island of Madagascar 50 years ago and the birds that laid them, Sir David has returned to the island off the east coast of Africa for a new BBC documentary on a quest to discover what happened to the largest birds to ever live on the planet.
The egg was laid by an elephant bird, which were more than 10 feet tall and weighed around half a ton, but what caused the huge birds to die out has remained a mystery, with some claiming they were hunted to extinction by humans and others blaming climate change.
But Sir David claims there is now compelling evidence that suggests the birds were gradually killed off by the early human inhabitants on the island stealing the giant eggs for food. He believes the birds themselves were revered by the indigenous populations, but the use of their eggs for food, combined with the destruction of the forests where the elephant birds lived, led to their eventual demise.
Recent archaeological evidence has revealed the fragments of elephant bird egg shells among the remains of human fires, suggesting that the eggs, which are 180 times bigger than a chicken egg, regularly provided food for entire families.
Sir David says: "I doubt it was hunted to extinction – anyone who has seen an ostrich in a zoo knows that it has a kick which can open a man's stomach and an enraged elephant bird, many times the size of an ostrich, must have been a truly formidable opponent.
"I suspect it was its egg. They may not have been able to tackle an adult bird, but they could have taken its eggs which would have been a huge source of food.
"Even if the bird itself was held in awe or fear by the people here, it's unlikely the eggs were – and that would have meant the gradual disappearance of this unique giant."
Sir David first travelled to Madagascar in 1960 when he was filming for the TV series ZooQuest. While there he discovered a few fragments of thick shell around the camp where he was staying in the south of the island and began offering a reward to the locals if they could bring him more.
He said: "A little boy brought in some big pieces that looked as though they fitted together, which indeed they did."
Using sticky tape he pieced together the fossilised egg, which is bigger than a rugby ball, before having it professionally stuck together when he arrived back in London.
As part of the new BBC documentary, Attenborough and the Giant Egg, Sir David returns to Madagascar to trace the story of what happened to the elephant birds by revisiting some of the places he went to on his original trip while also looking at some of the most recent scientific evidence.
Radiocarbon dating of bones and shells have suggested that the birds were still present on the island around 1,000 years ago. Humans are thought to have arrived on Madagascar around 2,000 years ago.
European sailors visiting the islands during the 1600s brought back stories of the giant birds and came back with the huge eggs while some reports state the last of the giant birds died out in the 1700s.
Experts, however, believe the birds largely vanished from the island around 1,000 years ago, although they may have clung on in small remote pockets on the island.
During the programme charting his quest to discover more about the bird, Sir David has his own egg dated using radiocarbon dating and discovers it is much older than he had thought – around 1,300 years old.
Dr Tom Higham, deputy director of the radiocarbon accelerator unit at Oxford University's research laboratory for archaeology, said: "We have done dating on quite a few elephant bird eggs and when we looked back at the dates we were getting, the youngest were around 900AD. The populations of humans on the island increased around that time too.
"Sir David had read a lot of the literature that suggests the birds were still around until much more recently, so I think he was surprised by how old it was."
Sir David also fears that the fate suffered by the elephant bird provides a cautionary tale for the damage being done to the environment in modern Madagascar, which is leaving many other species, including rare Lemur, critically endangered.
Speaking to The Sunday Telegraph, he said: "This is the first film I have made where I deliberately go back to a place I knew long ago and chart the changes that have taken place.
"I go back to a place where there was forest 50 years ago when I was there and it has all been knocked down the only thing that is there is an abandoned saw mill. It was sad to go back and see that.
"It is an example of the way the island has changed over the years. There are now three times as many people living on the island since I was there 50 years ago. The only places they can live and grow food were the only places that were wild. The wild places are being taken over by people building villages on them and rice fields."
* Attenborough's Giant Egg will be shown on BBC Two in the New Year along with the series Madagascar.
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