About 8,000 frog bones sat packed into a single ditch beside the line of England’s A14 Cambridge to Huntingdon road scheme, and a puzzle that has stood for roughly ten years now has a proposed answer. Birds of prey did it. Researchers from Bournemouth University and the Museum of London Archaeology (MOLA) conclude that short-eared owls and hen harriers hunted young frogs across open ground and left the remains behind.
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The bones came out of the ground between 2016 and 2018 during construction archaeology on the National Highways scheme. The new paper, “An Owl’s Eye View: Human-Animal Entanglement at the Roman Fen Edge,” appeared in the journal Environmental Archaeology on Nov. 10. Dr. Paul Clarkson of Bournemouth University led the work after seeing news of the discovery and contacting MOLA.
Frog humeri and a winter kill in the first year of life
The Bournemouth and MOLA news release reports that radiocarbon dating at the University of Vienna places the remains about 1,700 years ago, in the Roman period. The ditch filled within a single year, so the deposit is a short, sharp event rather than a slow accumulation. By measuring the frogs’ upper arm bones, or humeri, the team found that most animals died young, eaten in the winter of their first year of life. Clarkson had already built a bone-sizing method for amphibian remains, described in an earlier Environmental Archaeology paper on a medieval manor site in Dorset, where size was used to infer age at death.
The full paper is cited in the release by its DOI, although the publisher’s page could not be opened for this report.
Earlier descriptions of the same deposit were more cautious. MOLA’s own website account, which credits zooarchaeologist Vicki Ewens with the bone analysis, called the sheer quantity of remains, all concentrated in one place, surprising. That account, about the Bar Hill settlement, counted at least 350 individual frogs and toads, noted that most of the bones came from a 14-meter ditch beside a roundhouse, and found no cut marks, cooking signs or tooth marks. It floated several ideas: crop processing that drew insects and then frogs, animals trapped during spring migration, a harsh winter, or disease such as ranavirus. A report in The Past repeated those options and described the site as Middle to Late Iron Age, a range that ends at AD 43 and sits earlier than the Roman date in the new release. The two descriptions have not been reconciled in anything read for this report.
Retreating Fen water, cleared woodland and an owl’s hunting ground
The new explanation depends on landscape change. As Fen waters retreated, they created good breeding conditions for frogs, so the population boomed. At the same time, woodland was gradually cleared for grazing livestock, leaving open grassland of the kind owls hunt over and fewer trees to shelter the frogs. Snail, pollen and charcoal evidence supported the picture of a more open landscape, according to the release.
Clarkson said the mystery of the frogs has been solved, describing a feast of frogs eaten by a group of owls, whose bones were left behind. The release is more measured about the culprits themselves: short-eared owls and hen harriers are named as the most likely suspects, a wording that signals inference from the bones’ age profile, season and setting rather than direct evidence of a particular bird. That distinction matters for a claim this size.
The single-year fill is what gives the deposit its force. A ditch that took one year to fill, combined with frogs that were mostly in their first winter, ties the bones to one short episode rather than to generations of slow accumulation, which is why a predator working across a season fits better than a gradual build-up of natural deaths. The release also notes that the puzzle took about ten years to resolve from the first excavation, a reminder of how long bone assemblages can wait for the right comparison.
Seasonal grazing and what the frogs say about people
The frogs also say something about the people nearby. The researchers suggest the findings may indicate that people visited the area seasonally to move livestock to new pastures, rather than living there permanently. A permanent village would be expected to shape the landscape differently, whereas a pattern of grazing visits could clear woodland without leaving heavy domestic debris. Ewens said even the smallest animal recovered on a site can help archaeologists understand past environments and human activity.
One loose end sits in the release itself. It says the paper is free to read in “The Journal of Human Paleoecology,” yet the paper is listed in Environmental Archaeology, so readers hoping to check the humerus measurements should look under the latter. The larger unanswered question is the date: if the Bar Hill ditch is Iron Age, as the earlier MOLA-linked reports say, or Roman, as radiocarbon at Vienna now indicates, the match between the owls’ hunting ground and the cleared grazing land depends on which period the cleared woodland belongs to.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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