Comparing space use behavior and aviary-based exploration measures in a species rapidly expanding its geographic range

Kelsey McCune, Cody Ross, Christa LeGrande, Corina J Logan 

Species range expansions could be facilitated by consistent behavioral differences between individuals on the range edge relative to those in other parts of the range. Movement behaviors in particular are thought to be important for expanding and invasive species. There is evidence for a relationship between consistent individual differences in exploratory behavior and dispersal (the permanent movement an individual makes from its birth site to the place where it reproduces), but it is still unknown whether individual differences in exploration propensity relate to daily adult movement patterns within the home range (``space use''). Evidence suggests that daily space use behavior can vary consistently among individuals, but no studies have examined the relationship between empirical space use behavior and aviary-based measures of exploration, or space use behavior in different populations along an expanding range. Here, we studied a range-middle and range-edge population of great-tailed grackles (\textit{Quiscalus mexicanus}), a species that is rapidly expanding its geographic range. We evaluated whether performance on an exploration task in captivity related to subsequent space use behavior in the wild, measured using home-range size, mean and variation in log movement velocity (step length per time), and spatial location preferences. We found that exploration performance was related to space use in the wild for the range-middle (Arizona) population but not the range-edge (California) population. The movement behavior of Arizona grackles was also related to the number of breeding and food sites within their home ranges. Moreover, we found that California grackles had significantly larger home-range sizes, but lower average movement velocities than Arizona grackles. Our results indicate that individual differences in exploration, measured in captivity, do seem to be a contributing mechanism explaining variation in space use in the wild. However, context dependent environmental factors, such as the presence of important resources or population proximity to the edge of the range can have a large impact on some aspects of daily space use patterns. To further clarify how behavior influences invasion success, future studies are needed to investigate additional edge--middle population pairs for daily space use and alternative personality traits, like activity or aggression.