Egyptian Book of the Dead Depiction
© Wasef et al, 2019
A scene from the Books of the Dead (The Egyptian Museum) showing the ibis-headed God Thoth recording the result of the final judgement.
An analysis of ancient DNA extracted from the mummified remains of sacred ibises suggests ancient Egyptians captured the birds from the wild rather than farming them.

In Australia, the white ibis is unceremoniously referred to as a bin chicken, for its propensity to scavenge scraps from rubbish bins.

But in ancient Egypt, its relative, the sacred ibis (Threskiornis aethiopicus), was revered.

It was seen as a living representation - or even physical manifestation - of the God of Wisdom, Thoth, perhaps because it looks like a scribe writing on water when it dips its long slender beak into the water to feed.

Archaeologists have unearthed several million mummified ibises from a roughly 800-year period between 600 BCE and 250 CE.

Unlike victual mummies, which were buried in a person's tomb to come alive in the afterlife, ibis mummies were usually what's known as votive mummies.

These would have been purchased from a temple devoted to the God Thoth and displayed as an offering, much like candles or sticks of incense in Buddhist temples today.

After a period of time, the ibis mummies - some roughly wrapped in bandages, others exquisitely decorated - were moved into catacombs, vast underground tunnels and storage rooms beneath the temple.

"You go down into one of the catacombs, and you find streets full of rooms and all of those rooms are full of jars and all of those jars are full of mummies of ibis," says Sally Wasef, a palaeogeneticist at Australia's Griffith University.

An enduring mystery is how the priests running the temples kept up with demand. One theory, says Wasef, is that priests domesticated and reared the birds in hatcheries and farms near the temples. But archaeological evidence of such an operation is lacking.

To figure out where the birds could have come from, Wasef and colleagues turned to ancient DNA, even though the unforgiving heat of Egypt doesn't provide the ideal conditions for preservation of the ancient biomolecule.

Wasef extracted DNA from 40 ibis mummies from five different Egyptian catacombs. Fourteen of these yielded complete mitochondrial genomes, segments of the genome inherited through the maternal line.

The genomes were not closely related to each other, even if they were from the same catacomb. In fact, the genetic diversity of the mummies was similar to that seen in modern-day ibis populations from across Africa. (The birds are now locally extinct in Egypt.)

The finding rules out ibis farming, says Wasef. If the bird was farmed, she says, the mitochondrial genome for birds in the same catacomb would be similar to each other.

Instead, Wasef suspects the priests might have captured the birds - or their eggs - from the wild, raising them for short periods each year.

"It's really intriguing," says Linda Evans, an Egyptologist at Australia's Macquarie University, who was not involved in the study.

Evans says that although large farming operations were probably unlikely, there is evidence in artwork from the Old Kingdom that Egyptians domesticated geese. Additional artwork from the New Kingdom period - which just precedes the mummification period - shows geese and ibises together.

"Some breeding attempts might have been made as well," she says.

The relationship between Egyptians and other animals could also be revealed with ancient DNA.

The study was published in the journal PLoS ONE.