Owls behind ancient 'feast of frogs' mystery

The culprits behind a massive frog cemetery that has baffled scientists have turned out to be a group of short-eared owls.

Between 2016 and 2018, 8,000 ancient frog bones were discovered in a single ditch near the site of an Iron Age roundhouse at Bar Hill, near Cambridge.

Scientists at Bournemouth University and Museum of London Archaeology (MOLA) have now identified that birds of prey were behind the 1,700 year-old cold case.

Dr Paul Clarkson, of Bournemouth University, said people "don't often get an owl's eye view of what it was like in the past from archaeological sites".

The researchers compared the damage to the frog bones to previous studies, finding they had most likely been eaten by short-eared owls and hen harriers.

Archaeological evidence also showed the ditch filled within a single year.

The university team used a new method of analysis to discover that 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 1,700 years to Roman period.

The fen wetlands were retreating in the valley in the Roman period, creating ideal conditions for the frogs to breed in.

Large areas of woodland were gradually felled over time for grazing livestock, which then left the amphibians with fewer trees to protect them from the grassland hunters.

Clarkson said the solution to the mystery was "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," he said.

Senior zooarchaeologist Dr Vicki Ewens said she had "so many theories" before the solution was found.

She said the research showed "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".