Stable isotopes reveal captive vs wild origin of illegally captured songbirds in France

Abstract

Naturally occurring stable isotopes of several elements are important tracers in the study the wildlife ecology including the identification of origins for migration research, investigations of trophic relationships, and in the forensic determination of illegally harvested and captive fauna. Extensive illegal trapping for use as decoys and in cuisine has contributed to drastic declines of Ortolan Bunting Emberiza hortulana populations breeding and migrating through France. We contrasted feather hydrogen isotope (δ2Hf) values in illegally captured and subsequently confiscated Ortolan Buntings (n=234), including feathers known to have grown in captivity (n=34) or of unknown growing environment (wild or cage), with δ2Hf values in birds legally caught (ringed and released) in the wild (n=40). We sought to determine if feathers from these bird groups could be differentiated based on this single isotope. Feathers grown in captivity had considerably lower δ2Hf relative to feathers of wild birds, which is potentially indicative of tap water consumption and the use of different diets in captive birds. Further, applying mixing models to δ2Hf values revealed similar proportions of captive vs. wild origins for birds illegally captured in 2012, 2014 and 2015, and a larger proportion of individuals with feathers grown in the wild in 2013. This potentially mirrors the confiscation of birds at poaching sites only in the former years, but also of recently caught wild buntings kept captive in 2013. Our results show that even a single stable isotope (δ2H) with good association with origins where feather keratins are produced is potentially useful in understanding origins of captive birds and may advance the monitoring of illegally captured birds.