Data: Behavioral flexibility is similar in two closely related species where only one is rapidly expanding its geographic range

Human modified environments are rapidly increasing, which puts other species in the precarious position of either having the ability to adapt to a new area or, if they are not able to adapt, they must move to a different area if able. 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. Great-tailed grackles (*Quiscalus mexicanus*; GTGR) and their closest relative, boat-tailed grackles (*Quiscalus major*; BTGR) are social, polygamous species. The former is rapidly expanding their geographic range by settling in new areas, ​​whereas the latter are not. We previously found that GTGR are behaviorally flexible, however not much is known about BTGR behavior, which provides an ideal way to test the hypothesis that behavioral flexibility plays a key role in the GTGR rapid range expansion using the comparative method. We compared behavioral flexibility of GTGR from two populations across their range (an older population in the middle of the northern expansion front: Tempe, Arizona, and a more recent population on the northern edge of the expansion front: Woodland, California) with BTGR from Venus, Florida to investigate whether the rapidly expanding GTGR are more flexible. We found that both species, and both GTGR populations, have similar levels of flexibility (measured as food type switching rates during focal follows). Our results elucidate that, while GTGR are highly flexible, flexibility may not be the primary factor involved in their successful range expansion. If this were the case, we would expect to see a rapid range expansion in BTGR as well. This adds further support to our previous findings that persistence and flexibility variance play a larger role in the edge GTGR population. The evidence that two closely related species with similar levels of flexibility, but different range expansion rates does not support the hypothesis that flexibility is the primary facilitator of rapid geographic range expansions into new areas.