Bioaccumulation of metals in a critically endangered migratory songbird, the Yellow-breasted Bunting ( <i>Emberiza aureola</i> )

The bioaccumulation of metals can cause negative effects on the health status and body condition of wildlife. However, research in this field is strongly biased toward Europe and North America. Here, we investigate metal and metalloid concentrations in the feathers of a once common but now critically endangered migratory songbird, the Yellow-breasted Bunting (Emberiza aureola). Feathers were sampled in Thailand but most likely molted in China, where the species stops over during migration, and therefore likely relate to background pollution levels at these stopover sites. We detected chromium, copper, manganese, iron, lead, tin, and zinc (Zn) in 100% of the samples, whereas arsenic was detected in 9% and mercury as well as cadmium in 2% of the individuals. Most importantly, we found a weak but significant negative association of Zn concentration and individual body condition. Lower body condition could limit successful migration and ultimately lead to higher fitness costs and reduced survival in this threatened species. We call for studies to investigate whether elevated Zn exposure in Yellow-breasted Buntings is linked to mining activities or to the recent increase in Zn-biofortified rice planted in Asia to combat human Zn deficiency.