Tracking 4000 years of raptor diets through isotope analysis reveals urban scavenging with implications for conservation

Birds of prey (‘raptors’) often consume anthropogenic foods and can be closely associated with human settlements. In medieval Britain, birds of prey were commensal animals, especially in towns where biological waste was abundant. However, the antiquity of this relationship has not been well explored. In this study, we used stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) in bone collagen to investigate the dietary niches of red kites Milvus milvus, common buzzards Buteo buteo and white-tailed eagles Haliaeetus albicilla of Chalcolithic or Early Bronze Age, Iron Age, Roman and medieval periods from archaeological sites across southern and midland England and in Orkney (Scotland). Stable isotope values of raptor bones recovered from Iron Age Danebury, Roman Winchester, and medieval Oxford were consistent with the exploitation of livestock waste from food produced for human inhabitants. Combining all samples, bone collagen δ¹³C values were significantly less negative and δ¹⁵N values significantly higher in red kites and common buzzards from archaeological sites across Iron Age, Roman and medieval England than those of modern birds (dating from the late 20th and 21st centuries), and both species showed greater variability among individuals. The diets of historic birds may include prey from higher trophic levels and reflect a more generalist strategy. These data are consistent with the consumption of larger quantities of anthropogenic food waste including carrion from scavengers and slaughtered and farmed livestock animals, which is reduced in volume in today's landscapes. Archaeological raptors may also have exploited a wider range of scavenged or hunted prey in the absence of rabbits Oryctolagus cuniculus, a key prey item for modern-day raptors.