Reduced levels of relatedness indicate that great-tailed grackles disperse further at the edge of their range

It is generally thought that behavioral flexibility, the ability to change behavior when circumstances change, plays an important role in the ability of a species to rapidly expand their geographic range. However, it is an alternative non-exclusive possibility that an increase in the amount of available habitat can also facilitate a range expansion. Great-tailed grackles (*Quiscalus mexicanus*) are a social, polygamous species that is rapidly expanding its geographic range and eats a variety of human foods in addition to foraging on insects and on the ground for other natural food items. They are behaviorally flexible and highly associated with human-modified environments, thus offering an opportunity to assess the role of behavior and habitat change over the course of their expansion. Here, we compare behavior in wild-caught grackles from two populations across their range (a more recent population in the middle of the northern expansion front in Arizona versus a very recent population on the northern edge of the expansion front in California) to investigate whether individuals in a more recently established population exhibit more dispersal behavior (i.e., individuals are more likely to move away from their parents). We find that levels of relatedness are lower in the population closer to the edge compared to the population nearer the core. In particular, we observe no closely related individuals at the edge, suggesting that individuals of both sexes disperse further in this population than in the population nearer the core. Our analyses also suggest that, in both populations, females generally move shorter distances from where they hatched than males. These results elucidate that the rapid geographic range expansion of great-tailed grackles is associated with individuals differentially expressing dispersal behaviors.