Historical continuity in Sonoran Desert free-range ranching practices: Carbon, oxygen, and strontium isotope evidence from two 18th-century missions

Carbon (δ¹³C), oxygen (δ¹⁸O), and strontium (⁸⁷Sr/⁸⁶Sr) isotopes from cattle, caprine, and small mammal teeth from two historic-period Spanish missions, and modern cattle, were assayed with the goal of reconstructing historic ranching practices in the Sonoran Desert of southwestern North America. δ¹³C values from modern cattle indicates it is possible to distinguish cattle free-ranged within upper elevation desert habitats (-11.9 to -7.8‰) from lower elevations or possibly foddered animals (-2.5 to 0.8‰). It is not possible to distinguish maize-foddering versus low elevation free-ranging of livestock in the Sonoran Desert; however, the data indicates free-ranging occurred in both upland and lowland ecosystems, with some animals exhibiting evidence of a mixed upland/lowland strategy. δ¹⁸O values in mission livestock (-3.0 to 2.5‰) overlap with modern cattle (-3.1 to -0.1‰) watered from evaporated reservoirs, suggesting missions managed water for livestock, and livestock were likely kept away from riparian zones. ⁸⁷Sr/⁸⁶Sr results demonstrate that livestock were moved, likely through trade, some coming from a minimum distance of 40 km. Taken together these results are consistent with continuity in Sonoran Desert free-ranged herd management from the historic era to present. These results also point to continuity in water management strategies extending well prior to the colonial period.