We’re very excited to reveal our ancient frog mystery has been solved!

Back in 2022 we shared about the discovery of over 8,000 frog bones in a single Iron Age ditch during excavations on the National Highways A14 Cambridge to Huntingdon Improvement Scheme. There were lots of theories about what had killed so many amphibians in such a small area, but no solid answers

After seeing the discovery in the news, Dr Paul Clarkson at Bournemouth University contacted our Senior Zooarchaeologist, Dr Vicki Ewens. Thanks to Paul's analysis this unusual murder mystery has been solved – and the culprits are a real hoot!

Following the clues

Having compared the damage to the frog bones to previous studies, Dr Clarkson found they had been eaten by birds of prey. The most likely suspects are short-eared owls and hen harriers.

But the story doesn't end there. Our archaeological evidence from the site shows the ditch filled within a single year. This left us with a big question - how did so many bones appear in such a short period of time? The Bournemouth team investigated further...

By measuring the size of the frog humeri (arm bones) – a pioneering new method of analysis – they discovered most of the frogs died young, having been eaten in the winter of their first year of life. Radiocarbon dating by the University of Vienna also showed the remains dated back 1700 years to Roman period. 

During this time the Fen waters were retreating in this valley, creating ideal conditions for the frogs to breed. This meant plenty of young frogs for the birds to eat.

This valley was wooded in the Iron Age, but short-eared owls hunt over grassland. This suggested there were more landscape changes as the Fen waters retreated. Our team turned to snail, pollen, and charcoal evidence to find out more. Their analysis revealed that large areas of woodland were gradually felled in the late Iron Age for grazing livestock. By the Roman period, large patches of open ground left the frogs with fewer trees to protect them from the grassland hunters.  

Dr Paul Clarkson said:

“We don’t often get an owl’s eye view of what it was like in the past from archaeological sites. The mystery of these frogs has been solved - a feast of frogs that were eaten and their bones left behind by a group of owls. These bones not only tell us about life for people living near the Roman Fens, but they also give insights into the natural world - what wild animals were getting up to in the past, and what life was like for them.” 

Solving this puzzle also provides fascinating clues about how people used this landscape during the Roman period. If communities were visiting the area on a more seasonal basis to move livestock to new grazing pastures, this meant the fields would be less crowded, making it easier for the birds to hunt. 

Dr Vicki Ewens concludes:

“I had so many theories as to why such as large collection of frog bones were recovered from this small feature. It’s been great to collaborate with Paul to finally answer this question. This research shows how even the smallest animal recovered on a site can help us to understand not only past environmental conditions but human activity within a wider landscape.” 

The full research paper ‘An Owl’s Eye View: Human–Animal Entanglement at the Roman Fen Edge’ is free to access on The Journal of Human Paleoecology.  

The full digital archive for the A14 project can be accessed on the Archaeological Data Service.

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