August Sevchik, Corina J Logan , Kelsey McCune, Aaron D Blackwell, Carolyn Rowney, Dieter Lukas 

In most bird species, females disperse prior to their first breeding attempt, while males remain closer to the place they hatched for their entire lives. Explanations for such female bias in natal dispersal have focused on the resource-defense based monogamous mating system that is prevalent in most birds. In this system, males are argued to benefit from philopatry because knowing the local environment can help them to establish territories to attract females, while females are argued to benefit from dispersing because they can find suitable unrelated mates. However, theoretical, field, and comparative studies highlight that the factors shaping dispersal decisions are often more complex. Studying species with different social and mating systems can help illuminate the relative role of various factors in the evolution of sex biased dispersal. Here, we use genetic approaches to determine whether females and/or males disperse in great-tailed grackles (*Quiscalus mexicanus*), which have a mating system where the males hold breeding territories that multiple females might choose to place their nest in, but females forage independently of these breeding territories across a wider area. First, we find that, for individuals caught at a single site in Arizona, the average relatedness among all female dyads is higher than average relatedness among other individuals at the site, whereas average relatedness among all males dyads is not. Second, we find that female close relatives are found within shorter distances from each other than pairs of unrelated females, whereas male close relatives are found at larger distances from each other than pairs of unrelated males. Third, we find a decline in relatedness with increasing spatial distances for females, but not for males. Our results indicate sex biases in relatedness structure that differ from most other bird species. Female great-tailed grackles associate with close genetic relatives, presumably by remaining close to where they hatched which would lead to them remaining close to their mothers and sisters. Males are not found close to genetic relatives, suggesting that they disperse away from their fathers and brothers. Our findings show that great-tailed grackles offer a relevant study system to further understand the factors shaping natal philopatry and dispersal, given this reversal of the usual sex-bias in dispersal in line with their divergent social and mating system. Version 5 of this preprint has been peer-reviewed and recommended by Peer Community In Ecology (https://doi.org/10.24072/pci.ecology.100074)