Black-billed Magpies (Pica hudsonia) are a relatively sedentary corvid, with greater dispersal of females than males. To genetically confirm that dispersal pattern, 29 reproductively active adults were captured over two years and were scored for primer-specific random amplified polymorphic DNA (RAPD) bands (53 polymorphic bands in 1996 and 104 in 1997). In both years, we captured more previously banded males than females, and individuals recaptured were more often the heaviest nestling in their brood from the previous years. Genetic distances between all possible adult pairs were calculated and degree of genetic similarity between pair-wise comparisons was assessed using the Mantel test. In the pair-wise comparison of genetic distances, data for both years showed that genetic distances between males were significantly less (P < 0.05) than those for other adult combinations (male–female and female–female). Using the same analytical approach, we found that females were no more genetically similar to one another (P > 0.05) than were random pairs of adults. Group-distance analysis using the computer package RAPD also showed higher genetic similarity among males than among females. We suggest that a plausible hypothesis to account for the relatively high genetic homogeneity of the breeding male population compared to the female population is that a long-lasting intraclutch dominance hierarchy exists among siblings. That hierarchy is sufficiently long-lasting to influence the breeding population, resulting in alpha males remaining in the natal area, whereas lower ranking birds, including females, are forced to disperse.