Deciphering seasonal variations in the diet and drinking water of modern White‐Tailed deer by in situ analysis of osteons in cortical bone

Abstract

In situ carbon and oxygen isotope values for bioapatite were obtained from longitudinal slices of cortical bone from modern domesticated sheep and free‐range White‐Tailed deer. The analyses were obtained using an IR‐laser coupled to a GC‐IRMS interface. Ablation pits averaged 200 × 50 μm, making it possible to sample individual or small bundles of osteons. Cortical bone is remodeled along osteons throughout a mammal's life. Therefore, data at this scale can record seasonal variations in diet and drinking water during the adult stages of a mammal, whereas teeth provide may provide information about the juvenile years of a mammal. Average δ18O and δ13C values for the sheep from southwestern Ontario, Canada, were 14.0 and −16.1‰, respectively. No trend was observed in the isotopic composition of the sheep's osteons, consistent with its constant diet and water supply. The δ18O (14.2 to 16.6‰) and δ13C (−19.2 to −15.6‰) values of osteons from White‐Tailed deer from nearby Pinery Provincial Park, however, varied systematically and were negatively correlated. Oxygen isotope values of the osteons correlated well with changes in the δ18O values of the main water source for these deer: winter average, −10.7‰; summer average, −8.6‰. The variation in δ13C values of the osteons reflects changes in diet; summer diet consisted mainly of leafy C3 vegetation (−28.4‰), whereas winter diet comprised bark (−25.6‰), C4 grasses (δ13C, −12.7‰), and corn stalks and husks (−11.3‰).