Department of Biology

Winging it: Aggressive female tree swallows lead the charge in a range expansion and cope better with anthropogenic change

Dr. Lynn Siefferman
Appalachian State University

February 10, 2023
1-2pm Sullivan 101

Hosted By Melanie Stadler

Abstract

Aggressive female tree swallows (Tachycineta bicolor) can give us ecological insights into how organisms are able to thrive in our changing world. Using two studies, I show geographic and local patterns suggesting that animals with aggressive personalities may fair better in the face of environmental constraints. In animals, a consensus is emerging that ‘pioneering’ traits may facilitate range shifts via a set of bold, aggressive, and stress-resilient traits. These traits are associated with more northern latitudes, and most range shifts in the northern hemisphere indicate northward movement. As a consequence, it is unclear whether pioneering traits are simply corollaries of existing latitudinal variation, or whether they override other well-trodden latitudinal patterning as a unique eco-geographic rule of phenotypic variation. Tree swallows are moving southward in the eastern United States, in direct opposition of the movement in most other native species’ range shifts. Because this organic range shift countervails the typical direction of movement, this case study provides for unique ecological insights on organisms and their ability to thrive in our changing world. We found that females at more southern expansion sites displayed higher maternal aggression, higher baseline corticosterone, and more pronounced elevation of corticosterone following a standardized stressor, contrary to otherwise largely conserved latitudinal patterning in these traits. Thus, we show that pioneering traits are not simply corollaries of existing latitudinal variation, but rather, they may override other well-trodden latitudinal patterning as a unique eco-geographic rule of phenotypic variation. Next, at our local North Carolina field site, we tested whether more aggressive tree swallow mothers dealt better with anthropomorphic change during the breeding season. While parents were rearing young, we manipulated human-induced noise, a disturbance that is becoming more prevalent in natural settings as road networks continue to expand. We found that when traffic noise is great, nestlings grow more slowly. However, the offspring of mothers that are more aggressive to predators were not adversely affected by the noise. Assessment of animal personality may improve our understanding of how animal populations will respond to anthropogenic change.