Ancient humans were 'farming' cassowaries 18,000 years ago

Researchers found that while younger cassowary eggshells from New Guinea showed evidence of being cooked, the eggs of almost fully formed cassowaries did not. This, the scientists suggest, indicates that the birds may have been hatched and raised. 

As the shells date to thousands of years before chickens and geese were domesticated, the raising of cassowaries may be one of the earliest examples of humans managing wild birds. 

Dr Kristina Douglass is the lead author of this new paper that has looked into the ancient cassowary eggs and the potential management of the birds. 

'This behaviour that we are seeing is coming thousands of years before domestication of the chicken,' says Kristina. 'And this is not some small fowl, it is a huge, ornery, flightless bird that can eviscerate you.' 

The research, led by scientists from Pennsylvania State University, was published in PNAS.

Egg timer 

Cassowaries are large, flightless birds found in Papua New Guinea, southern Indonesia and northern Australia. They belong to a group known as ratites, which also includes ostriches, emus and rheas. 

The evolutionary history of the ratites is uncertain, but it is generally believed that as the ancient continent of Gondwanaland split the ancestors of these big birds diverged into the variety of species we see today scattered across the southern hemisphere. 

In the case of the cassowary, it became limited to the humid rainforests of Australasia where it evolved into three species of large, solitary, mostly fruit-eating birds. Adults maintain large territories, which they aggressively defend using the large claws which adorn their feet. 

As a result, the cassowary doesn't seem like an obvious candidate for being raised by humans. 

But despite this, the birds are actually reared and hunted on the island of New Guinea to this day. This new research suggests these traditions could date back tens of thousands of years. 

The egg remains were discovered during excavations of two rock shelters, known as Yuku and Kiowa, on New Guinea where prehistoric humans are known to have lived. The sites offer an insight into these ancient people's diet, with the remains of bats, marsupials and birds found. 

Amongst these were the remains of eggshells from cassowaries, most likely the dwarf cassowary on the basis of bone fragments found alongside them.  

To date these fragments, the researchers took samples from ostrich eggs at different stages of development, which were used to develop a model estimating how old a developing chick would be. Other assessments were also carried out by eye. 

Dr Douglas Russell is the Senior Curator of Birds at the Museum and was not involved in the study. He says that even though the comparison was between different species, it was likely valid. 

He has previously looked at the extinct great auk's eggs to examine how the structure of the eggshell compares with modern relatives like the guillemot. This allowed for inferences to be made about the great auk's breeding biology. Similar work has focused on older specimens. 

'There's a team at York who have been looking at eggshell in middens and archaeological sites in the UK, and we provided them with a lot of material in the past,' Douglas says. 'Utilising modern material to try and understand historical issues has certainly been done before.'  

For the cassowaries, the researchers used the appearance and structure of the egg to estimate how old the chick would have been at the time the eggshell was broken.  

'What we found was that a large majority of the eggshells were harvested during late stages,' said Kristina. 'The eggshells look very late; the pattern is not random. They were either into eating baluts [an almost developed chick eaten as street food] or they are hatching chicks.' 

Early birds 

They also looked for evidence of burns, to infer whether or not the eggs had been cooked. They found evidence that the younger eggs may have been cooked intact, as most of the burns were on the outside only. Intermediate eggs showed burn marks inside and out, suggesting the developing chick was cooked, while the older eggs showed few signs of being burnt at all. 

The researchers claim this is evidence that the older chicks were being specifically hatched and raised by prehistoric humans, like their descendants in modern New Guinea today. Cassowaries can imprint on people, so they could be raised believing the humans were their parents. 

The exact purpose of raising the chicks is unclear, but as modern New Guineans use cassowaries for food, traditional ceremonies and for trade, it is possible their ancestors could have been doing something similar. 

The discovery also pushes back the earliest relationships between birds and humans by thousands of years, with researchers saying their find could 'represent the earliest indication of human management of the breeding of an avian taxon anywhere in the world.' 

While their find is earlier than the estimated domestication of the chicken around 10,000 years ago, there is some evidence Neanderthals and humans could have harvested rock doves in Gibraltar from as early as 68,000 years ago. 

More studies of this kind are likely in the future, as our technology becomes better at investigating the remains of the past.  

Douglas says: 'Going forward, our ability to study eggshell at very high levels of magnification allows us to revisit and explore material which we couldn't have even begun to analyse until fairly recently.'