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 adapting to a new area or, if they are not able to adapt, shifting their range to a more suitable environment. 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. To determine whether species differences in range expansion propensity are linked to differences in behavioral flexibility, we compared two closely related species, great-tailed grackles (Quiscalus mexicanus; GTGR) and boat-tailed grackles (Quiscalus major; BTGR). The former is rapidly expanding their geographic range by settling in new areas, ​​whereas the latter is 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 comparative perspective adds further support to our previous intraspecific findings that persistence and flexibility variance play a larger role in the edge GTGR population than in the GTGR population away from the edge. Our research indicates that the hypothesis that flexibility is the primary facilitator of rapid geographic range expansions into new areas needs to be revisited.