| Abstract | Methylmercury (MeHg) is an environmental contaminant that has harmful effects on wildlife. Anthropogenic sources, like coal-burning power plants and gold mines, emit inorganic mercury (IHg) into the atmosphere. Inorganic mercury deposited from the atmosphere into aquatic ecosystems is converted to MeHg by bacteria and can enter the food web. Emergent aquatic insects (e.g. dragonflies) can transport MeHg from the aquatic ecosystem to terrestrial predators like songbirds. This project focuses on MeHg contamination of nestling Red-winged blackbirds (Agelaius phoeniceus) at the Eagle Mountain Hatchery Pond Facility (near Fort Worth, Texas). Nestling Red-winged blackbirds (RWBL) consume emergent aquatic insects, primarily odonates (damselflies and dragonflies), but can consume terrestrial prey (e.g. caterpillars, beetles) as well. Odonates are have high concentrations of MeHg in their tissues while terrestrial prey has low MeHg concentrations (Speir et al. 2014). Although previous studies have attempted to observe what RWBL parents feed nestlings, there are no studies of the actual prey composition in the nestlings' digestive tracts. The identity of insects consumed by birds can be determined by examining bird fecal matter because insect body parts (head capsules, mandibles, legs) are composed of undigestible chitin. In my study, I identified fragments of insects in the fecal sacs of RWBL nestlings to determine the composition of aquatic and terrestrial prey in their diets. Emergent aquatic insects were consumed by the nestlings, explaining the presence of MeHg in the nestling blood but most of the prey in fecal sacs were terrestrial prey, explaining why the concentrations of MeHg in the nestling blood were relatively low and below a risk threshold for MeHg. |
