Spacing patterns, mating systems, and winter philopatry in Harlequin Ducks

Many species of waterfowl form pair bonds during the nonbreeding season, ye t current descriptions of mating systems and patterns of philopatry in wate rfowl focus on the breeding grounds. We studied wintering Harlequin Ducks ( Histrionicus histrionicus) in southwestern British Columbia to examine mati ng systems and philopatric behavior outside of the breeding season. The num ber of males at our study area was far more variable than that of females. Males that were unsuccessful in obtaining a mate were observed over a large r area than were paired males. Habitat use overlapped considerably among pa ired males, and no territorial boundaries were formed. Annual return rates to the nonbreeding grounds were high for both sexes (62% for females, 77% f or males). Individuals not only returned to the general study area, but als o to specific sections within the study area. Males that did not pair in th e previous year returned to the study area in the subsequent year with the same frequency as males that had obtained mates; however, they tended to le ave the study area prior to courtship. Therefore, it is possible that males return to the same wintering grounds each year to reunite with a previous mate. High levels of philopatry by both sexes allow pairs to reunite in fal l, potentially increasing the benefits of philopatry for both sexes.