Behaviour 2019
Behavioral, physiological and morphological patterns of the tree swallow’s unusual southward range shift
Lynn Siefferman1, Alexandria Albers2, Kimberly Rosvall3. 1Appalachian State University, Boone, NC, United States; 2Appalachian State University, Boone, NC, United States; 3Indiana University, Indiana, IN, United States

Organisms are facing unprecedented environmental changes, and many species are responding to these environmental changes via shifts in their range. Certain robust behavioral, morphological, and physiological traits may promote success during range shifts including aggressiveness, and stronger immune and stress responses. The tree swallow (Tachycineta bicolor) can test the generality of these mechanisms; this species is undergoing a southward range expansion in the eastern US, contrary to global climate models. We sampled birds across seven populations in their historic and expansion range, and measured glucocorticoid signaling, anti-predator aggression, hematocrit and mass. Expansion sites females were more robust, behaviorally and physiologically: they had higher hematocrit, aggression, and strongly elevated stress-induced corticosterone. Expansion site females were also marginally smaller than those at historic sites, but did not differ in baseline corticosterone. These findings suggest that pioneering syndromes may transcend the specifics of range shifts, with certain traits promoting success in novel environments, even when they countervail typical latitudinal patterns.