Correlates of Harlequin Duck densities during winter in Prince William Sound, Alaska

We evaluated relationships of Harlequin Duck (Histrionicus histrionicus) densities to habitat attributes, history of habitat contamination by the 1989 Exxon Valdez oil spill, and prey biomass density and abundance during winters 1995-1997 in Prince William Sound, Alaska. Habitat features that explained variation in duck densities included distance to streams and reefs, degree of exposure to wind and wave action, and dominant substrate type. After accounting for these effects, densities were lower in oiled than unoiled areas, suggesting that population recovery from the oil spill was not complete, due either to lack of recovery from initial oil spill effects or continuing deleterious effects. Prey biomass density and abundance were not strongly related to duck densities after accounting for habitat and area effects. Traits of Harlequin Ducks that reflect their affiliation with naturally predictable winter habitats, such as strong site fidelity and intolerance of increased energy costs, may make their populations particularly vulnerable to chronic oil spill effects and slow to recover from population reductions, which may explain lower densities than expected on oiled areas nearly a decade following the oil spill.