(PhysOrg.com) -- Sir David Attenborough has returned to the island of Madagascar to discover the fate of the elephant bird, the largest bird ever to live on Earth, and to make a BBC documentary about it: "Attenborough and the Giant Egg."
Fifty years ago Sir David collected a giant fossilized egg over 25 cm long and has kept it in his cellar ever since. The bird that laid the egg was around three meters tall, weighed over 450 kg and roamed the island until perhaps as late as a few centuries ago. It is not known what caused the extinction of the elephant bird, but theories include the effects of climate change, human hunting, and the diseases that came with the domesticated fowls that accompanied the humans.
Madagascar is an island of the east coast of Africa, which Sir David first visited in 1960 to film an episode of Zoo Quest, a popular TV series. After finding fragments of a fossilized shell, he offered the locals a reward if they could find him more pieces, and a little boy presented him with a complete set of fragments Attenborough later had professionally stuck together.
Humans are believed to have arrived in Madagascar about 2,000 years ago, but the elephant bird and humans coexisted for many centuries. Sailors visiting Madagascar in the 17th century returned to Europe with reports of seeing the giant birds, and with samples of the eggs. It is thought that the birds were fully extinct by the early 18th century.
Researchers now believe that most of elephant bird populations had disappeared by about 1,000 years ago and only those in remote parts of the island survived. Dr. Tom Higham of the research laboratory for archaeology at Oxford University said they had dated quite a few elephant bird eggs and the youngest they had found was dated at about 900 AD, a time at which the human population was expanding. Sir David had his own fossil egg dated and found it was about 1,300 years old, much older than he had thought.
Sir David says there is now compelling evidence the human inhabitants of the island stole the eggs for food, even though they revered the birds themselves, and the nest raiding plus destruction of the native forest habitats led gradually to their extinction.
Evidence for the theory comes from recent archaeological findings of shells of elephant bird eggs among the remains of ancient camp fires, which suggest the eggs were used for food. At around 150 times the volume of a hens egg, one egg would easily feed a number of families.
It is unlikely that the giant bird, which was much bigger than todays ostrich, was hunted to extinction, according to Sir David, who thinks stealing the eggs and loss of habitat were much more likely cause of their demise.
In the new documentary Sir David examines the latest evidence and returns to some of the sites he visited 50 years ago, the first time he has deliberately returned to a place he had previously visited. He said 50 years ago the forest in the area was extensive, and now all that is left is an abandoned saw mill. The human population on the island has tripled, and all the previously wild places are being replaced with villages and rice fields. The changes leave many other species, including the rare Lemur, now critically endangered.
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