Mercury Contamination Of Spiders And Their Risk To Songbirds At LBJ National Grassland, Texas

Abstract

Methylmercury (MeHg) is an environmental contaminant that can have adverse effects on wildlife. Because MeHg is produced by bacteria in aquatic ecosystems, MeHg has primarily been viewed as a problem to aquatic food chains, but recent studies have found high levels of MeHg in terrestrial feeding songbirds. In the present study, the authors examined the risk that MeHg-contaminated terrestrial long-jawed orb weaver spiders (Tetragnatha sp.) pose to songbirds at the Lyndon B. Johnson (LBJ) National Grasslands. The authors collected spiders in June 2013 and June 2014 from 14 ponds and found that MeHg concentrations in spiders varied both spatially and temporally. The authors then calculated spider-based wildlife values for the American Robin and the 12-day-old Carolina Chickadee to assess exposure risk for arachnivorous birds. Concentrations of MeHg in spiders exceeded the wildlife values for the 12-day-old Carolina Chickadee, but not for the larger American Robin. This MeHg threat to songbirds may not be unique to the LBJ National Grassland and may extend throughout the 8 million ponds that occur in the United States.