Proximity to metal mining is related to aspects of feather coloration but not fluctuating asymmetry in the Russet-crowned Motmot (Momotus mexicanus) in south-central Mexico

Mining is present in all major biomes worldwide and overlaps strongly with areas of importance for bird conservation. Mining causes multiple types of environmental disturbance, including habitat alteration, increased human presence and persistent heavy metal pollution. Feather coloration and fluctuating asymmetry (random deviation from perfect symmetry between the two sides of the body), especially of elaborate or ornamental characters, have been proposed as potentially useful biomarkers of anthropogenic stress in birds. However, there has been virtually no research on their responses to mining disturbance. Here, we use colour and morphometric measurements and collection location data from museum specimens of the Russet-crowned Motmot Momotus mexicanus to evaluate how their proximity to mining concessions in south-central Mexico (Morelos, Guerrero and Oaxaca states) relates to: (1) structural and melanin-based plumage coloration, and (2) size and fluctuating asymmetry of their distinctive racket-shaped tail. As a resident, philopatric bird that has been observed nesting directly in contaminated mining waste, motmots may be particularly well suited for addressing this question. In birds collected closer to metal mines, the violet under-eye spot had decreased UV-blue chroma and the black eye streak was paler, and there was weaker colour contrast between these adjacent conspicuous facial plumage patches. Body, tail and crown colour and tail length and asymmetry were unaffected by metal mine distance, and no variable was affected by distance to mines extracting non-metals. Overall, our findings show that aspects of motmot coloration are affected by mining disturbance, probably more from heavy metal contamination rather than other aspects of mine-related anthropization. Further research is needed to determine whether these effects are due to direct toxicity or to ecological effects such as decreased food availability and to discern whether altered colour of conspicuous patches affects social processes such as mate choice and territorial interactions in populations exposed to mining.