New method to detect illegal wildlife trafficking

Estimated at $7 billion to $23 billion annually, the illegal wildlife trade is the world’s fourth largest criminal market. Yet under the 1973 Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES ), some trade in endangered, protected, or exploited species is permitted, provided the animals come from certified breeding farms. Far too often, animals caught in the wild are passed off as captive-bred, and forensic tools for determining an animal’s identity, geographic origin, and legal status have limited accuracy, availability, and affordability. Most evidence for geographic origin currently comes from isotopic analysis of metabolically inert tissues such as hair, feathers, horns, or quills, which record the animal’s diet and habitat when the tissue is synthesized. (See Physics Today, January 2004, page 20 .) Isotopic analysis, however, is expensive and destroys the samples, and its usefulness is largely limited to species with small home ranges and restricted diets.

Kate Brandis of the University of New South Wales and colleagues have shown that high-resolution x-ray fluorescence can offer a noninvasive, nondestructive, low-cost alternative for forensic classification. As a proof of principle, they examined quills from short-beaked echidnas (see the photo); half the quills came from zoo specimens and half from wild animals. The researchers recorded the x-ray-induced fluorescence at points in 200-micron increments along the length of each quill and, from the peaks in each spectrum, derived the abundances of 24 different elements. (Isotope analysis, in contrast, typically looks at 1–2 elements.) Abundance variations between points on the same quill reflect temporal changes in diet and metabolism.

Using a machine-learning algorithm, the researchers found that the element data from a single measurement point could classify a quill as captive or wild with 96% accuracy, compared with only 92% for isotopic analysis of carbon-13 and nitrogen-15; combining all the fluorescence measurements along a quill yielded perfect classification. The sample size was small and the geographic extent was limited, so the team is continuing to explore the technique’s potential—including using handheld equipment that could be deployed in markets, on farms, and at ports. (K. J. Brandis et al., Sci. Rep. 8, 15380, 2018 ; photo by KeresH , CC BY-SA 3.0 .)