More than 9,000 bones found in an ancient ditch near Cambridge belonged mainly to frogs that were eaten by short-eared owls (Asio flammeus) about 1,800 years ago. Previously, researchers suggested the remains might be linked to a Roman feast or some ritual, but a new study published in the journal Environmental Archaeology has shown that the bones most likely remained after the birds' winter hunting.
The ditch was discovered during preliminary archaeological work for construction of a section of the A14 motorway between Cambridge and Huntingdon, at the edge of the Fen wetland area. People lived in this area as early as the Middle and Late Iron Age, when a shallow channel about 20 meters long was dug. At first, archaeologists mistook it for the remains of a roundhouse.
The purpose of the ditch could not be determined, but 9,135 small bones were found inside. The majority belonged to common frogs (Rana temporaria), but the remains also included bones of voles, shrews, snakes and other small animals.
To determine how these animals died, researchers studied more than 1,700 bone remains. No traces of fire, butchery or teeth that could indicate human consumption were found on them. In addition, the ditch was not deep enough for frogs to fall into it en masse and become trapped. At the same time, traces of digestion were found on nearly 86% of the frog bones.
The study's lead author, archaeologist Paul Clarkson of the University of Bournemouth, noted that the nature of the damage allowed the likely predator to be identified with clarity. The bones were sufficiently degraded by digestion to rule out barn owls, but not sufficiently damaged to attribute them to otters, snakes or herons. The combination of characteristics pointed to short-eared owls (Asio flammeus), which likely hunted the frogs over the course of just one winter.
The value of this find lies not in the number of bones itself, but in how the past landscape can be read from them. When the ditch is compared with the surrounding area, it becomes clear that conditions for frog breeding were created by the coincidence of human activity and changes in water levels, and the owls simply took advantage of the resulting abundance. This is a rare opportunity to see at one site the interaction of climate, agriculture and wildlife at the same time.
The methodology is also noteworthy. The degree of wear on the bones allowed researchers to rule out other predators and retain only one option: the short-eared owl. Such conclusions are not always final, since they rely on comparative data, but in this case the argument sounds quite clear.
The next step is likely to be the search for similar sites during other excavations. If the same pattern is repeated, the remains of small animals will become a common tool in archaeology rather than an accidental find.
