The shortening observed in the archaeological specimens appears to be the result of the creeper mutation. This affects the length of all the limb bones, but the shortening is particularly pronounced in the legs, notably in the tibiotarsus, the longest bone in the leg (the main bone in a chicken drumstick). This is not only disproportionally short but is usually bowed backwards to some extent, and the lower ends of the fibula and tibiotarsus are fused. Movement is restricted compared to fowl that don’t have the condition; badly affected individuals may not be able to stand because of twisting of the tibiotarsus shaft and some have permanently curled toes. Mortality is high in chicks with the creeper gene and any that are homozygous for the condition (gene present on both chromosomes) die in the egg. However, despite the downsides, the condition has been considered desirable by poultry breeders and it has become the distinguishing character of various modern breeds including Scots Dumpies in Britain, Courtes Pattes in France, Creepers in the United States, and Japanese bantams. The creeper chickens from Canterbury sites are of a consistent size and appear to be a particularly diminutive form. The number of occurrences suggests a local interest in poultry breeding, most likely among people of an elevated social status. The fact that the chickens have been identified from deposits spanning the Roman through to early post-medieval period in Canterbury, and from a range of sites, suggests that the character may have been actively maintained, perhaps even as a distinct ‘breed’.