We have known for years that more aggressive females are able to secure a breeding territory -- they get to breed when less aggressive females do not (Rosvall 2008). But even among females who do obtain a nesting site, there is marked variation in aggressiveness. Does aggressiveness shape reproductive success? How about longevity or other elements of Darwinian fitness?

To address these questions, my lab has assembled a dataset of ~3000 tree swallows, including > 150 breeding attempts each year for nearly a decade. Outside of studies of mammalian dominance hierarchies, this is the most comprehensive long-term dataset on competitive behavior in wild female animals. We have multi-phenotype data on all chicks, mothers, and adults, including ~500 aggression scores obtained from hundreds of females, some for multiple years from their birth to their death. Current members have begun mining these data, and we are partnering with IU's ASURE program to use this database to begin population genetic analyses as well.

Tree swallows are expanding their breeding range southward, contrary to the 80% of organisms that are moving to higher latitudes and higher altitudes as our world changes.

With collaborators at Cornell University, we have found that stress-related gene expression in the brain varies within and among these populations (Zimmer et al 2023). With collaborators at Appalachian State University, we have shown expansion and historic core populations also differ in maternal (anti-predator) aggression and associated hormonal mechanisms. We have shown that populations vary in multiple elements of their thermal tolerance, including their brain's sensitivity to heat (Woodruff et al. 2022) and their behavioral response to heat (unpubl. data collected in collaboration with the Derryberry lab).

Stay tuned as we work to understand the integrated set of behavioral and physiological traits that allow tree swallows to thrive as they expand their range to breed in warm areas of the American Southeast.