Reproductive, immune, and physiological end points in tree swallows on reclaimed oil sands mine sites

Wild nestling tree swallows (Tachycineta bicolor) inhabiting reclaimed wetlands receiving tailings or water from mine tailings ponds on oil sands mine sites were the subjects in a multiyear study to determine the ecological viability of these areas. Spanning two field seasons, immune function, reproductive performance (clutch size and mass, hatching success),nestling growth and survival, and diet of tree swallows were examined on six wetlands. One aspect of immune function, the T-lymphocyte proliferative response, was assessed in vivo using a phytohemagglutinin skin test. Hepatic ethoxyresorufin-O-deethylase (EROD) activity provided a biomarker of exposure to oil sands contaminants in the tree swallow nestlings. Results show that there were no differences among reclaimed wetland sites for tree swallow reproductive success, nestling growth rate, and immune response that could be attributed to tailings or tailings pond water additions. Increased EROD activity confirmed the presence of xenobiotics in the diets of nestlings from two sites, while the main reference site was relatively free of EROD-inducing compounds. Dietary analyses showed that 84% of the food items of the tree swallow nestlings were of aquatic origin, likely from the local wetlands, and thus would be expected to provide a good reflection of biological effects of any mining-related contaminants accumulating through the food chain.