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They were mummified in their millions. Stacks and stacks of sacred ibises were interred roughly 2,500 years ago as prayer offerings. At one site alone there are 1.75 million ibis mummies – where did the Egyptians get all these birds?

DNA locked inside some of the avian mummies has now been extracted and analysed. The findings suggest that the birds were not reared on large industrial-scale farms as described in ancient hieroglyphs, but rather captured from the wild before sacrifice and mummification.

at Griffith University in Australia and colleagues ground up powdered bone and tissue from 40 well-preserved ibises. They then extracted DNA from the mitochondria, the energy-generating component in cells, using molecules designed to bind to it.

The team used mitochondrial DNA because even in ancient samples there’s a good chance that it has been preserved. There are around 1,000 copies of it in each cell, says Wasef.

From 40 mummified ibises, the team managed to sequence 14 complete mitochondrial genomes.

They compared these with mitochondrial DNA from 26 modern day wild ibises and found a similar pattern of diversity. Had generations of the birds been reared on large farms, one would expect their DNA to be less diverse, a result of breeding bottlenecks

Wasef and her colleagues say that this shows that the ibises used in mummification were not taken from small, inbred populations.

“It’s an impressive bit of work,” says , at the University of Aberdeen.

However, as the team only examined a small number of ibises, another explanation could be that birds were farmed on a large scale but topped up with wild birds regularly, says Collinson. “There could be an inbetweeny answer,” he says.