Stable isotopes are considered as nature’s ecological recorders. Its application in the study of the ecological phenomenon in plants and animals is increasing day by day. Understanding the dietary food habits, migratory pattern, natal origin, and trophic position of any organism is helpful to a conservationist to understand their behavior and recognize the type of habitat they reside.

Tracing origin and movement patterns:

Stable isotopes as one of the biogeochemical markers are the most suitable methods to trace the origin and migration of wildlife like birds, insects, and mammals ^1–3. To understand animal behaviour, and their ecology, it is necessary to know it movement pattern. For this we need to track individual or population on a seasonal or annual basis. Tracking animals can be done either directly or indirectly. Firstly, direct tracing includes the following individual over time and space through remote-sensing techniques like radio transmitters, or individual tag like leg rings, neck collars. In direct tracking method, an animal needs to be captured and recaptured and also, it could not be viable to small animals and long distance travellers. Secondly, indirect tracking of individual could achieve by using their (plant and animals) intrinsic biological (genetic variation) or biogeochemical marker (stable isotopes) ^4–6. Stable isotope analysis does not require marking and recapturing individuals and can work with large populations at a time in broader scale of time and space.

How does it work?

Stable isotope signature in animal tissues reflects local food web ¹, location, and habitat ³. These chemical signatures can be applied as a tool to reconstruct animal movement pathways ⁷. Variation in chemical

signatures reflects the chemical environment and were not attributable to sex or random deposition ⁷. It lies on the fact that the mineral profile in the tissues of organism varies micro-geographically, and its various stages of development and migrated locality have a considerable effect on various trace element composition ^3,8–10. The isotopic signature of any animal caught at one location can be compared with those of individuals caught at another location ⁴.

Summary and Future Research:

The application of stable isotopes in revealing the biological and ecological phenomenon of plants and animals is increasing day by day. Understanding dietary habits, migratory pattern, natal origin of any organism is extremely important for a conservationist to understand organismal behavior and recognize the type of habitat necessary for the conservation and management. The stable isotopes of carbon, nitrogen, oxygen, hydrogen, and sulfur are mostly commonly used in ecological, biological and hydrological studies.

As improved and new isotopic techniques evolve, it becomes less time consuming, cheaper and requires smaller sample sizes. Collaborating stable isotope analysis with other advanced techniques like remote sensing and genetic approaches can solve more complex dietary and other ecological and trophic position in a food web. For example, both microsatellites DNA variation and hydrogen stable isotope ratios were used to determine the population connectivity and migration patterns of Wilson’s warbler (Wilsonia pusilla) ¹¹. Combining, genetic and isotopic approaches could give more reliable and precise results, which could address both important issues for conservation efforts and also investigate the evolution of migration.

Consequently, stable isotope application has applied in organisms from big birds to small bugs, from giant elephant to tiny ant, from gigantic whales to microscopic benthic plankton in aerial, terrestrial, and aquatic ecosystem respectively. Its application is interdisciplinary in nature. I believe, stable isotope methods if stand with other technologies will have incredible potential to answers, the previously considered difficult or impossible ecological questions. There are many unknown and thrilling directions in which this field could proceed.

1. Hobson, K. A. Tracing origins and migration of widlife using stable isotopes: a review. Oecologia 120, 314–326 (1999).
2. Hobson, K. a. Using stable isotopes to trace long-distance dispersal in birds and other taxa. Divers. Distrib. 11, 157–164 (2005).
3. Szép, T. et al. Comparison of trace element and stable isotope approaches to the study of migratory connectivity: An example using two hirundine species breeding in Europe and wintering in Africa. J. Ornithol. 150, 621–636 (2009).
4. Rubenstein, D. R. & Hobson, K. A. From birds to butterflies: Animal movement patterns and stable isotopes. Trends in Ecology and Evolution 19, 256–263 (2004).
5. Hobson, K. a, Wunder, M. B., Van Wilgenburg, S. L., Clark, R. G. & Wassenaar, L. I. A method for investigating population declines of migratory birds using stable isotopes: origins of harvested lesser scaup in North America. PLoS One 4, e7915 (2009).
6. Mazerolle, D. F. & Hobson, K. A. Estimating Origins Of Short-Distance Migrant Songbirds In North America: Contrasting Inferences From Hydrogen Isotope Measurements Of Feathers, Claws, And Blood. Condor 107, 280 (2005).
7. Ethier, D. M., Kyle, C. J., Kyser, T. K. & Nocera, J. J. Trace elements in claw keratin as temporally explicit indicators of geographic origin in terrestrial mammals. Ann. Zool. Fennici 50, 89–99 (2013).
8. Szep, T., Moller, a P., Vallner, J., Kovacs, a & Norman, D. Use of trace elements in feathers of sand martin Riparia riparia for identifying moulting areas. J. Avian Biol. 34, 307–320 (2003).
9. Poesel, A., Nelson, D. a., Gibbs, H. L. & Olesik, J. W. Use of trace element analysis of feathers as a tool to track fine-scale dispersal in birds. Behav. Ecol. Sociobiol. 63, 153–158 (2008).
10. Neuhauser, J. Using Trace Elements to Chemically Fingerprint European Starlings. (2013).
11. Clegg, S. M., Kelly, J. F., Kimura, M. & Smith, T. B. Combining genetic markers and stable isotopes to reveal population connectivity and migration patterns in a neotropical migrant, Wilson’s warbler (Wilsonia pusilla). Mol. Ecol. 12, 819–830 (2003).