The bald eagle (Haliaeetus leucocephalus) is an extensively researched tertiary predator. Studies have delineated information about its life history and the influences of various stressors on reproduction. Due to the bald eagles position at the top of the food web, it is susceptible to biomagnification of a wide array of xenobiotics. In Michigan the bald eagle population has recovered strongly since the population bottle-neck of the 1960s. In the 1960s when Michigan's eagle population was first being monitored less than 100 nests were occupied yearly (i.e., active breeding pairs existed). Today there are approximately 500 occupied nests each year and over 700 breeding areas in the state.;Because p,p'-dichlorodiphenyltrichloroethylene (p,p'-DDE), PCBs and Hg are often all found in individual nestling eagles and eagle eggs it is hard to establish a causative effect between individual persistent chemical and declined reproduction. Field studies and laboratory work has shown a correlation between p,p'-DDE, PCBs, and Hg concentrations and decreased reproduction success. In the shell gland of birds, DDE inhibits the action of carbonic anhydrase which is necessary to supply the carbonate ions used in shell formation. PCBs have been correlated with dead and deformed embryos of water birds in the upper Great Lakes. Field and laboratory studies have also correlated Hg concentrations with behavioral changes, which may disrupt foraging and nesting.;The Michigan Department of Environmental Quality (MDEQ) implemented a monitoring program using the bald eagle to monitor trends of persistent chemicals under the Clean Michigan Initiative in 1999. These monitored persistent chemicals included PCBs, organochlorine pesticides, and Hg.;The state was divided into major "watershed years" with 20% of Michigan's watersheds being sampled each year. This sampling procedure allowed for the entire state to be sampled and analyzed every five years. During annual banding activities, blood and feather samples from nestling bald eagles were collected within these designated watersheds. Monitoring contaminant trends at various spatial scales allows for comprehensive assessment of the Great Lakes Basin ecosystem health.;The objectives of this research were to evaluate spatial and temporal trends of Hg, PCBs and pesticides in nestling bald eagles of Michigan. For Hg, spatial and temporal trends were determined. For PCBs and pesticides only spatial trends were examined because some data were not available at the time of writing. As data become available further analysis will be conducted, including temporal trends.;In the first study "Using nestling bald eagles to track spatial trends of PCBs and pesticides in aquatic ecosystems of Michigan" we evaluated PCB and pesticide concentrations at three spatial scales. In summary, our study found that concentrations of PCBs and pesticides were significantly higher in Great Lakes areas with Lakes Michigan and Huron having highest concentrations of pesticides and Lake Erie having highest concentrations of PCBs.;In the second study "Using nestling bald eagles to track spatial and temporal trends of mercury in aquatic ecosystems of Michigan." we evaluated Hg concentrations at four spatial scales and three temporal periods. In summary, our study found that Hg concentrations where significantly greater in the Upper Peninsula of Michigan and inland areas and that while concentrations have decreased from those of the late 1980s they are currently increasing across the state.;Continued monitoring of bald eagle populations is suggested for several reasons. First, nestling blood and feather contaminate levels have been shown to be an appropriate method to monitor ecosystem contaminant levels. Both blood and feather samples can be collected during routine nestling banding activities. Second, both PCB and pesticide concentrations for 37% and 40% of the nestling eagles sampled were above the no observable adverse effect level for bald eagles. Thus, it is possible that once these nestlings reach sexual maturity, they may not be able to reproduce at a level considered necessary to support a healthy population due to elevated concentrations of DDE or PCB. Lastly, with Hg concentrations on the rise, adverse effects including decreased reproduction could occur in bald eagles. The Upper Peninsula of Michigan should be concentrated on because of its characteristics which lead to increased bioavailability of Hg. With the current concentrations of PCBs and pesticides and increasing Hg concentrations this ongoing research may be in a unique position to document the threshold at which detrimental effects from persistent xenobiotics occur in the bald eagle.