Data from: Do metal mines and their runoff affect plumage color? A regional scale study of streak-backed orioles in south-central Mexico

Metal mining causes serious ecological disturbance, due partly to heavy
metal (HM) pollution that can accumulate at mining sites themselves and be
dispersed downstream as runoff. Plumage coloration is important in birds’
social and ecological interactions and sensitive to environmental
stressors, and several local-scale studies have found decreased
carotenoid-based plumage and/or increased melanin-based plumage in wild
birds exposed to HM pollution. We investigated regional-scale effects of
proximity to mines and their downstream rivers as a proxy of exposure to
HM-contaminated mining waste on plumage coloration in streak-backed
orioles (Icterus pustulatus) in south-central Mexico. We measured the
plumage color of museum skins using reflectance spectrometry and digital
photography, then used geographic information systems to estimate each
specimen’s distance from the nearest mining concession and river and
determine whether that river’s watershed contained mines. Proximity to
mines and their downstream rivers was related to ventral (but not dorsal)
carotenoid-based coloration; birds collected farther from mines had more
vivid yellow-orange breast plumage, and belly plumage was more vivid and
redder with increasing distance from rivers with upstream mines. Breast
background reflectance unexpectedly decreased with mine distance and was
higher among birds whose nearest river had mines upstream. The area (but
not reflectance) of melanin-based plumage was also related to mines. The
area of dark back streaks decreased with mine distance, while the bib
patch was smaller among birds presumably more exposed to mining waste.
While some of these results are consistent with predicted effects of HM
pollution on plumage, most were not straightforward, and effects differed
among plumage patches and variables. Further investigation is needed to
understand the direct (e.g., toxicity, oxidative stress) and/or indirect
(e.g., decreased availability of carotenoid-rich food) mechanisms
responsible and their individual, population, and community-level
implications.