Oxygen isotope values in bone carbonate and collagen are consistently offset for New World monkeys.

Stable oxygen isotopes are increasingly used in ecological research. Here, I present oxygen isotope (δ(18)O) values for bone carbonate and collagen from howler monkeys (Alouatta palliata), spider monkeys (Ateles geoffroyi) and capuchins (Cebus capucinus) from three localities in Costa Rica. There are apparent differences in δ(18)Ocarbonate and δ(18)Ocollagen among species. Monkeys from moist forest have significantly lower isotope values than those from drier localities. Because patterns are similar for both substrates, discrimination (Δ) between δ(18)Ocarbonate and δ(18)Ocollagen is relatively consistent among species and localities (17.6 ± 0.9‰). Although this value is larger than that previously obtained for laboratory rats, consistency among species and localities suggests it can be used to compare δ(18)Ocarbonate and δ(18)Ocollagen for monkeys, and potentially other medium-bodied mammals. Establishing discrimination for oxygen between these substrates for wild monkeys provides a foundation for future environmental and ecological research on modern and ancient organisms.