Seasonality or short-term mobility among trophy head victims and villagers? Understanding late-life dietary change in the pre-Hispanic Andes through stable isotope analysis (δ¹³C/δ¹⁵N) of archaeological hair keratin and bone collagen

Objectives: This study aims to determine whether adults from the site of Uraca in the Lower Majes Valley, Arequipa, Peru altered their diets in late-life—if so, were those short-term changes related to accessing distinct foods during periods of short-term mobility, seasonal subsistence strategies without accompanying mobility, or some other type of short-term change. We address this question by comparing stable isotope variability (δ¹³C/δ¹⁵N) of Uraca hair keratin and bone collagen to published archaeological hair data from Peru. We propose and apply a landscape bioarchaeology approach—here, the spatially-informed meta-analysis of published δ¹³C/δ¹⁵N data from archaeological hair keratin of known provenience—to determine thresholds for different types of short-term dietary change. Materials and methods: We conducted stable isotope analysis (δ¹³C/δ¹⁵N) of archaeological hair keratin (n = 40 samples) and bone collagen (n = 5 samples) from Uraca, including adult male trophy heads and adult male and female villagers. We then compiled published archaeological hair keratin data from the Andes and coded the 11 sites according to biogeographical zones. We compared late-life averages for the entire dataset (n = 131 segments) and ranges for individuals with more than six months of data (n = 101 segments) between sites and between subgroups based on elevational zones, sex, and trophy subgroupings. We compiled archaeological and modern baseline food web data for the region (n = 401 samples) and compared hair data adjusted to diet. Results: Meta-analysis shows greater late-life median δ¹³C_{keratin (VPDB)} and δ¹⁵N_{keratin (AIR)} for yunga vs. coastal burials, greater δ¹³C_{keratin (VPDB)} ranges for coastal burials, greater δ¹⁵N_{keratin (AIR)} ranges for females, greater median δ¹⁵N_{keratin (AIR)} for trophy individuals, and greater δ¹³C_{keratin (VPDB)} ranges for trophy individuals. Given these distinct late-life diets and ranges for coastal and yunga burials relative to southern Peruvian food web data, two females and three trophy individuals from Uraca likely changed diets during a short-term move, while the remainder show no evidence for dietary change. Discussion: These analyses demonstrate distinct dietary practices between coastal and yunga groups, between males and females, and between trophy head victims and non-trophy villagers. Understanding the nature of late-life dietary change through a comparative synthesis of archaeological hair provides key insights into individual life trajectories, communal practices, mobility, and foodways relative to altitudinally-variable landscapes of the Peruvian Andes.