A rare bird egg is due to be auctioned at Sotheby's in London and it is thought it might fetch up to £50,000.

The egg comes from the now extinct Elephant bird, which was a flightless bird indigenous to Madagascar.

It is just over 30cm tall, 200 times as large as a chicken's egg, and the bird itself is thought to have been 3m tall and weighed in at around 450kg.