Stable isotope dating
Stable isotopes have helped uncover migratory routes, trophic levels, and the geographic origin of migratory animals.
They can be used on land as well as in the ocean and have revolutionized how researchers study animal movement.
Most elements exist in two or more forms, known as isotopes.
Isotopes have the same number of protons but differ in their number of neutrons, resulting in different masses. Determination of the migratory dynamics of the sooty shearwater in the Pacific using stable carbon and nitrogen isotope analyses. Carbon isotope ratio of feathers reveals feeding behaviour of cormorants.
The lighter form is generally the more common one (Hobson & Wassenaar 2008). Marine Ecology Progress Series 158, 249-246 (1997).
These values are calculated as follows: δ X = [(RC contains 6 protons, 6 electrons, and 7 neutrons. Estuarine, Costal and Shelf Science 16, 345-349 (1983). Therefore, an increase in the δ values denotes an increase in the amount of the heavier isotope component; while a decrease in the values denotes a decrease in the heavy isotope content (Peterson & Fry 1987). Stable isotope analysis is based on the principle ‘you are what you eat.' Stable isotope ratios vary among food webs and are incorporated into an animal's tissue via its diet (Hobson 1999). Migrations of California gray whales tracked by oxygen-18 variation in their epizoic barnacles. It is thus sometimes possible to infer the whereabouts of an animal moving between food webs. It is important, however, to choose the appropriate tissue for isotopic analysis, as tissues differ in how metabolically active they are (Rubenstein & Hobson 2004).