Researchers identify predators responsible for ancient Roman frog graveyard

Scientists at Bournemouth University and the Museum of London Archaeology (MOLA) identified birds of prey as the cause of a massive frog bone accumulation in a Roman era ditch.

The team analyzed a collection of 8,000 frog bones found between 2016 and 2018 during construction on the National Highways A14 Cambridge to Huntingdon Improvement Scheme. While the origin of the bones remained a mystery for a decade, researchers determined that short-eared owls and hen harriers likely consumed the frogs.

The researchers used a new method of measuring frog humeri to determine that most of the animals died young during their first winter. Radiocarbon dating by the University of Vienna confirmed the remains are 1,700 years old. The study suggests that retreating waters in the Fen region during the Roman period created perfect breeding grounds for the frogs, providing a concentrated food source for the birds.

Environmental evidence from snail, pollen, and charcoal samples showed that people cleared large areas of woodland for livestock grazing. This change in the landscape left the frogs exposed to grassland hunters. The findings indicate that human activity and seasonal livestock movement shaped the environment, allowing the birds to hunt more effectively in the open space.