Riparian Bird Occupancy in a Mountain Watershed in the Colorado Mineral Belt Appears Resilient to Climate-Change-Driven Increases in Metals and Rare Earth Elements in Water and Aquatic Macroinvertebrates

Abstract

Acid rock drainage (ARD) impacts species composition in mountain streams. The potential impact for riparian birds experiencing elevated metal uptake by consumption of benthic invertebrates is concerning but not well studied. We investigated the influence of metal and rare earth element (REE) content in benthic invertebrates on the presence of breeding birds in an ARD-impacted watershed in Colorado, USA, where tree swallows in nest boxes had previously been found to have elevated metal concentrations at some sites. The concentrations of particular REEs in invertebrates were higher than those for cadmium or lead. Avian point counts indicated that most bird species detected were present at most sites, and that tree swallows were rarely found. Occupancy models showed that the availability of shrub or forest habitat was a good predictor for a few habitat-specialists, but metal and REE concentrations in water and invertebrates were not good predictors of avian presence. For other species, neither habitat type nor water quality were important predictors. Overall, this study indicates that the climate-change-driven increases in metals and REEs may not influence the presence of riparian birds in ARD-impacted streams.