Use of tree swallows in studies of environmental stress

Tree swallows (Tachycineta bicolor) are common North American song birds and are increasingly targets of studies of the effects of environmental change on wildlife. This review examines previous work on use of tree swallows to study the ecological importance of environmental contaminants and other sources of environmental change. Exposure of tree swallows to chemical contaminants has been monitored at sites throughout the species' range. Major studies of environmental contaminants have been conducted on Green Bay, the Great Lakes, and the Hudson River where tree swallows are exposed to high levels of PCBs through their diet of insects with aquatic larvae. Additional studies have been completed examining possible effects on tree swallows of exposure to agricultural pesticides in orchards and effluent from pulp mills. In general these studies document that tree swallows are good indicators of exposure to chemical contaminants and their use as a model species has increased our understanding of the importance of biological transport of contaminants from aquatic sediments to the terrestrial food chain. Tree swallows appear to less sensitive to the effects of PCBs and related chemicals than previously studied species. Evidence of behavioral and developmental effects of PCBs is found in tree swallows exposed to high levels of PCBs along the Hudson River. In addition to studies of contaminants, tree swallows have been used in studies of acid deposition, radiation, and climate change. These studies show that tree swallows are sensitive to the ecological changes that can result from anthropogenic stressors impacting both terrestrial and aquatic ecosystems.