Winter Philopatry of Harlequin Ducks in Prince William Sound, Alaska

We used capture-mark-recapture data to assess winter philopatry by Harlequin Ducks (Histrionicus histrionicus) in Prince William Sound, Alaska, during winters 1995–1997 and 2000–2001. Philopatry was quantified using homing rates, which were estimated as the proportion of birds recaptured at their original site out of all recaptured birds. Between-year homing rates of 0.95 (95% CI: 0.87–1.00) and 1.00 (0.92–1.00) were estimated for females and males, respectively, at three locations on Montague Island. Similar homing rates were measured in western Prince William Sound, where estimates were 0.92 (0.80–0.98) for females and 0.96 (0.79–1.00) for males, with a scale of detected movements for all recapture birds ranging from 3–52 km. Our results indicate that wintering aggregations may be demographically independent at a much finer spatial scale than genetic data indicate, and that conservation efforts should recognize this degree of demographic separation among population segments.