| الوصف: |
This research assesses the ecotoxicology of three avian species in their natural environment. Field studies investigated potential toxicological effects of organochlorine pollutants including polychlorinated biphenyls (PCBs) and dichlorodiphenyl trichloroethane (DDT) and their metabolites on wildlife with passerine nestlings as model organisms. For organisms at higher trophic levels, especially terrestrial ones the major route of exposure to persistent pollutants is food. Consequently, I estimated the diet of nestlings of populations of three species - tree swallows (Tachycineta bicolour), purple martins (Progne subis) and house wrens (Troglodytes aedon) at Point Pelee National Park, Ontario, Canada and their contaminant contents. Another route of exposure in oviparous organisms is through their eggs, so the contaminant contents in eggs of each population were analyzed. Nestlings’ growth rates were measured in the field from which values consumption rates were estimated. Contamination loads were estimated by multiplying consumption rates by food-specific contaminant concentrations and combined with egg-acquired burdens in a bioenergetics-based model to predict bioaccumulation levels of various PCB congeners and DDE in each species. These estimates were compared with tissue contaminant concentrations of nestlings sacrificed at fledging age. The deviations between the predicted and observed values reflected the nestlings’ biotransformation and absorption abilities. To measure nestlings’ biological responses to organochlorine pollutants, house wren nestlings'’ diet was supplemented with Hexagenia mayflies collected from three locations containing different PCB burdens. Nestlings fed mayflies collected from a heavily contaminated site had significantly reduced relative growth rates and enlarged livers and hearts relative to controls (whose diets were not supplemented with mayflies) and to individuals fed mayflies from less contaminated sites. However, nestlings fed ‘reference’ mayflies that had been spiked with a PCB mixture grew at the same rate as nestlings fed with mayflies collected from a moderately polluted location, suggesting that contaminants other than PCBs were responsible for the observed impairments. The thesis results demonstrate that accumulation of pollutants and its effects on nestling passerines in natural habitats are based on composition of food, contributions from maternal burden accumulated from breeding and overwintering locations, and bioenergetics of nestlings including biotransformation capacities. |
