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By comparing the O-Sr isotope profiles of a control and transported horse, we investigated isotopic signal(s) potentially useful for reconstructing travel histories via high-resolution sequential sampling along single strands of tail hair. Improved analytical capabilities allowed for extremely low Sr abundance samples to be analyzed for Sr/ Sr and proved capable of resolving a horse's movement between distinct regions. Copyright © 2017 John Wiley & Sons, Ltd.

Rationale Strontium isotope ratios (87Sr/86Sr) of hair may be a valuable tool to estimate human provenance. However, the systematics and mechanisms controlling spatial variation in 87Sr/86Sr of modern human hair remain unclear. Here, we measure 87Sr/86Sr of hair specimens from across the USA to assess the presence of geospatial relationships. Methods Ninety‐eight human hair specimens were collected from salon/barbershop floors in 48 municipalities throughout the conterminous USA. [Sr] and 87Sr/86Sr ratios were measured from hair using quadrupole and multi‐collector inductively coupled plasma mass spectrometers, respectively. The [Sr] and 87Sr/86Sr ratios of hair were compared with the measured [Sr] and 87Sr/86Sr ratios of tap waters from the collection locations. In addition, the 87Sr/86Sr ratio of hair was compared with the modeled ratios of bedrock and surface waters. Results Hair color was independent of the 87Sr/86Sr ratio, but related to [Sr]. The 87Sr/86Sr ratios of hair and leachate were not statistically different and were positively correlated; however, in several hair‐leachate pairs, the ratios were conspicuously different. The 87Sr/86Sr ratios of both hair and leachate were linearly correlated with tap water. The 87Sr/86Sr ratio of hair was also significantly correlated with the modeled ratio of bedrock and surface waters, although the 87Sr/86Sr ratio of hair was most strongly correlated with the measured ratio of tap water. Conclusions The 87Sr/86Sr ratio of hair is related to the ratio of tap water, which varied geographically. The ratio of hair provided geographic information about an individual's recent residence. Differences in the 87Sr/86Sr ratios of hair and hair leachate may be concomitant with travel and could potentially be used as a screening tool to identify recent movements.

Building on applications in anthropology, the use of stable isotope ratio analysis of human bone collagen to investigate an individual’s life history is becoming more commonplace in the forensic science community. Careful consideration of the resultant isotope delta (δ) values, particularly in regard to their accuracy and reliability, is paramount when introducing isotope data into the U.S. court system. In this study, we use a simple framework to calculate real interpretative difference (RID) values for collagen (“col”) and assess isotope data comparability for sample analysis (RIDanalysis) as well as sample preparation/analysis combined (RIDcombined). The RIDcombined values of 0.59‰ for δ13Ccol and 0.91‰ for δ15Ncol are similar to more complex, published calculations of inter-laboratory variability in the stable isotope analysis of skeletal remains, but they are easier to calculate and intuitively elegant. The RIDcombined as well as RIDanalysis values presented here allow users to examine multiple sources of inter-laboratory isotopic variation (preparation, analysis, and both together) in a two-step  process whereby a RID value is constructed and then tested. Implementation of this RID approach will provide surety for the legal and research communities in forensic applications of stable isotope ratio analysis.