Migratory animals, their large distance movements and life cycles have eluded scientists for centuries, particularly for hard-to-track and tiny species like the iconic monarch butterfly. But thanks to the help of isotopic techniques, experts worldwide can better understand the flows and patterns of animal migration where traditional techniques have shown their limits.

World Wildlife Day 2020 celebrates "sustaining all life on earth" at a time when, more than ever, conservation plans are needed all around the world. Climate change, destruction of habitats for agriculture, illegal poaching and logging, pollution and use of pesticides are threats to animal species around the globe.

“The rate of species loss is exponentially higher than at any time in the past 10 million years. […] One million species are in near-term danger of extinction,” said Antonio Guterres, United Nations Secretary-General, to the General Assembly on 22 January 2020, urging for the adoption of the post-2020 global biodiversity framework.

To preserve the lives of migratory animals, isotopic techniques significantly contribute to identifying these animals’ origin, their breeding grounds, and wintering and intermediate stopover sites. Based on this scientific data, policy makers can develop better conservation methods for all sorts of animals, such as fish, birds, mammals or insects.

“Isotopic techniques offer an incomparable advantage over the traditional tracking methods, as they are non-invasive and do not necessitate the recapture of the same animals,” said Leonard Wassenaar, Head of the IAEA’s Isotope Hydrology Laboratory.

For over a century, conventional mark-and-recapture approaches used to track animal movement have relied on external markers, such as tags and radio and satellite tracking, which are inappropriate for small and short-lived animals. Then, in 1996, research by Leonard Wassenaar and Keith Hobson, who at the time were isotope scientists for Environment Canada, demonstrated that isotopic techniques can be used to determine the origin of individual animals.

Their research is based on measuring deuterium — a rare isotope of hydrogen — in rainwater, which is directly absorbed by plants or ingested by animals and humans. As rainwater and its deuterium composition are unique to the area where it rains, rainwater deuterium content serves as a direct marker that scientists can use to identify the origin of individual animals that were grown in different areas by measuring the amount of deuterium in hair, wings, claws, feathers or bones. For monarchs, the deuterium contents show the area where the insect was born.