Exploration and dispersal are key traits involved in a rapid range expansion

To the point

• Exploratory behavior: Grackles who were trained to be more flexible were more exploratory after the training than untrained grackles. This indicates that the more an individual investigates a novel object, the more it can learn and adapt its behavior accordingly.
• Range expansion: Grackles in an edge population disperse farther than those in a more central population. This suggests that the rapid geographic range expansion of great-tailed grackles is associated with individuals differentially expressing dispersal behaviors.
• Key traits: Flexibility, exploration, and dispersal are key traits involved in this species’ rapid expansion into new areas.

Behavioral flexibility, the ability to adapt one’s behavior to changing circumstances based on previous experience, is thought to play an important role in a species' ability to successfully adapt to new environments and expand its geographic range. New findings from researchers at the Max Planck Institute for Evolutionary Anthropology in Leipzig, the University of California Santa Barbara, and Auburn University, advance our understanding of the responses to novel circumstances by revealing flexibility in behavior on an individual level. These new results provide critical information for predicting which traits facilitate a species' ability to adapt its behavior to new areas, which is crucial in today's changing world.

Flexibility-trained grackles were more exploratory

The researchers investigated great-tailed grackles because they are an urban bird species that has rapidly expanded its range across North America over the past 140 years. Grackles who were trained to be more flexible were more exploratory after the training than untrained grackles.

“This shows that flexibility and exploration are linked - the more an individual investigates a novel object, the more it can learn and adapt its behavior accordingly,” says Corina Logan, a researcher at the Max Planck Institute for Evolutionary Anthropology and Gates Cambridge Scholar. These findings suggest that flexibility and exploration are key traits involved in this species’ rapid expansion into novel environments.

Just because it can be measured doesn’t mean it’s reliable

Large gaps exist in our knowledge of how behaviors relate to each other and the environment because researchers often rely on unvalidated behaviors or proxies to draw conclusions about how these systems work. To address this issue, the researchers in the current study measured four behaviors: exploration of new environments and novel objects, boldness towards known and novel threats, persistence, and motor diversity. However, only two of these behaviors, exploration of a new environment and persistence, were consistent across individuals. Consistency indicates that it is a stable trait that can be compared with other stable traits.

“Animals cannot tell us what they are thinking, so it's really important to ensure that our methods of quantifying behavior and cognition actually tell us what we want to know,” says lead researcher Kelsey McCune at the University of California Santa Barbara (currently at Auburn University). This highlights the importance of measuring multiple behaviors and validating their consistency before including them in analyses.

Grackles on the edge are less related, thus disperse farther

In a follow-up study, the researchers found that flexibility in behavior is linked not only to the exploration of novel environments on a small scale (e.g., a small tent), but also to novel spaces on a much larger scale. They found that grackles living closer to the edge of the expansion front in California exhibit greater dispersal behavior, with both male and female individuals moving farther away from their parents and siblings. In contrast, females in particular remained close to where they hatched in a population in the middle of the northern expansion front in Arizona.

“For a population to establish itself in a new area, many individuals of both sexes must move there,” says lead researcher Dieter Lukas at the Max Planck Institute for Evolutionary Anthropology. “The great-tailed grackles appear to have the flexibility to stay when they can, but to move when necessary.”

These results show that the rapid geographic range expansion of great-tailed grackles is associated with individuals expressing dispersal behaviors differentially.