• Develop approaches for predicting population-level responses to stressors, and identify 
the responses at the individual level that have the greatest influence on population-level 
responses (APG 3). 
• Develop mechanistically-based approaches for extrapolating toxicological data across 
wildlife species, media, and individual-level response endpoints (APG 4). 
• Develop approaches for evaluating the relative risks from chemical and non-chemical 
stressors on spatially structured wildlife populations across large areas or regions (APG 
5). 
The research described here attempts to make advances in each of these research areas through a 
single demonstration project designed to develop the tools and approaches necessaiy to conduct a 
multi-tiered assessment of the risks of PBTs, (e.g., mercury) to populations of piscivorous birds 
in New England and the upper Midwest. In the process of developing the approach and tools for 
conducting the risk assessment, we will also develop a framework for establishing wildlife 
criteria using piscivorous birds and Hg as the example. In conjunction with project Bl, the 
methods and models developed in this demonstration project will be evaluated for their 
applicability to other PBTs and other wildlife species. This demonstration project focuses on 
issues starting with the exposure of birds to mercury in the fish (and other dietaiy components) 
they consume, rather than focusing on fate and bioaccumulation within the wholly aquatic 
portion of the food web. Many of the issues addressed in the development of population and 
spatial models in this project should contribute to the development of more generalized 
approaches for assessing risks to wildlife species. 
It should also be noted that another component of this project involves the assessment of the 
interactive effects of landscape-level habitat alteration and mercury on loons. This project also is 
described in Section 4 (Habitat Alteration) because there are significant research issues regarding 
habitat alterations, including evaluating the spatial configuration of loon habitat and mercury 
impacts in the landscape mosaic and the issue of scaling up from local to regional impact 
assessments. 
Scientific Approach 
Mercury contamination remains a high priority issue for several EPA Program Offices and 
Regions because of widespread atmospheric deposition and concerns of accumulation through 
aquatic food webs. Although there is evidence of reduced productivity in some piscivorous birds 
and widespread reports of wildlife tissue mercury concentrations exceeding levels associated 
with adverse effects in controlled studies, it is unclear what impact this has on the viability of 
populations of piscivorous wildlife. Also, mercury contamination exists within a patchwork of 
other co-occurring stressors to wildlife populations, but the relative risks are poorly understood. 
Because mercury bioaccumulates in the aquatic food web, this demonstration project focuses on 
the risks of mercury to top level predators (piscivorous birds, in particular, common loons [Gavia 
immer]), associated with mercury exposure in the environment. Given the heterogeneous 
distribution of stressors (e.g., dietary methyl mercury, habitat degradation, acidification, human 
disturbance), the project will attempt to identify the spatial relationships among stressors (i.e.. 
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