Movement Patterns and Population Structure of Harlequin Ducks Wintering in the Strait of Georgia, British Columbia

I investigated winter movement patterns and population structure of Harlequin Ducks (Histrionicus histrioniczrs) in the Strait of Georgia, British Colunlbia, Canada. Because of winter pairing, delayed maturation, and long-term pair bonds, movement patterns at wintering areas, particularly those of young birds that have not yet paired, are important to population structure. I used nasal- and radio-marking to determine movement distances, and multi-stratum models In capture-mark-recapture analysis to estimate movement rates among locations. I provide evidence that Harlequin Duck broods accompany their mothers from breeding streams to coastal wintering areas. Behavioural observations of family-like groups at the coast, and genetic analysis of blood samples from putative family members, suggested that observed groups were true families. Family migration in combination with philopatry, in the absence of dispersal, would lead to juvenile recruitment into the wintering populations of their relatives, and potentially to genetic and demographically isolated populations. Winter movement distances and rates did not differ by sex, likely due to extreme philopatry of paired males, slightly reduced philopatry of unpaired males, and intermediate philopatry of previously paired females. However, they did differ by age, with young birds in their first and second winters dispersing greater distances and at higher rates than older individuals. Isolation by distance and stepping stone gene flow models generated estimates for the among population component of genetic variance of less than 1% for the Strait of Georgia. Thus, due to dispersal of young individuals, which counteracts the isolating effects of philopatry and family migration, groups of Harlequin Ducks are unlikely to be genetically distinct at this scale. However, estimates from the stepping stone model for an increased number of colonies did suggest that, due to their linear coastal distribution, genetic differences could develop at the scale of their entire west coast of North America wintering range. Low movement rates between the northern and southern Strait of Georgia suggested that groups of wintering birds may be demographically distinct at this scale, and dispersal by both sexes indicated that recolonization or rescue of extinct or reduced groups is likely.