Based on continued concern over recovery of the flora and fauna in the nearshore environment of Prince William Sound from the Exxon Valdez oil spill, studies of harlequin duck molting and wintering ecology have been conducted as part of the Nearshore Vertebrate Predator Project funded by the Exxon Valdez Oil Spill Trustee Council. Harlequin duck life history traits indicate that they may be particularly susceptible to oil effects. Much of the oil spilled from the Exxon Valdez was deposited in the nearshore intertidal and shallow subtidal zones, the coastal habitats where harlequin ducks occur. Harlequins appear to be highly philopatric to their molting and wintering sites; this is an adaptive behavioral strategy in natural situations and predictable environments, but does not accommodate movement to undisturbed sites in the face of human-caused perturbations. Also, Goudie and Ankney (1986) suggested that harlequins were on the lower end of body size for surviving in harsh environments similar to Prince William Sound in winter. Because harlequin ducks exist close to an energetic threshold, any perturbation (i.e., an oil spill) that either affects health or condition directly (via toxic effects) or indirectly (via food abundance) could have significant consequences for the population. Finally, among ducks, sea ducks represent the K-selected extreme along the r-K continuum (Eadie et al. 1988) and, of sea ducks, harlequin ducks are particularly K-selected (Goudie et al. 1994). Harlequin ducks typically defer reproduction for 3 years, have relatively low annual investment in reproduction, and are long-lived (Goudie et al. 1994). Species with these characteristics have relatively low potential rates of population change and, thus, following a perturbation such as an oil spill, require many years in the absence of continued adverse effects to recover to previous population levels. Aggregations of harlequin ducks in marine areas during non-breeding periods can be considered the core populations of concern with regard to oil spill recovery. Most of the annual cycle is spent on nearshore marine areas. Based on seasonal surveys of abundance in Prince William Sound and radio telemetry work as part of this study, the bulk of harlequin duck reproduction occurs outside of Prince William Sound. Thus, EVOS impacts are most likely to occur during nonbreeding periods, although effects may be expressed throughout the annual cycle. Thus, this research focuses on the molting and wintering ecology of harlequin ducks to determine if oiling history is an important factor affecting: adult female winter survival, winter distribution and abundance, molting female body composition, bioindicator indices to health, indices to oil exposure, and food abundance. This research will be used to assess recovery status and identify any demographic, health, or trophic factors that may be limiting population recovery. Finally, results from the harlequin duck work will be incorporated into a consideration of the nearshore environment in general.