Personality, Stress Profiles & Fitness in Eastern Bluebirds and Tree Swallows

Lynn's post-doctoral research focused on understanding the evolutionary significance of personalities in eastern bluebirds and gaining knowledge of and techniques in behavioral endocrinology. She conducted post doc work under the guidance of Dr. Ellen Ketterson at Indiana University. Differences in personalities similar to those familiar in humans (i.e. assertive, friendly, or aggressive) have been documented in wild animals including two species that I study: Eastern bluebirds and Tree swallows. The Siefferman lab studying whether personality affects mate-choice decisions, fitness and competition for breeding resources between conspecific and heterospecifics.

Tree swallows are extending their range southward and have been in the NC study area <40 years. At our field site, bluebirds and tree swallows are extremely aggressive towards one another and often the result of competition between tree swallows and bluebirds is eviction of the bluebird pair from the nest box. Morgan Harris' MS thesis (2014) demonstrated that bluebirds tend to mate with individuals of similar personality type. Further, he showed that interspecific competition between tree swallows and bluebirds influences the fitness benefits of pair similarity in personality (Harris & Siefferman 2014). This research can be used to shed light on how interspecific competition with aggressive invasive species can exert selection pressure on a less-aggressive, resident species and has far-reaching application in how behavior affects the vulnerability of species to invasions. Alex Albers' MS thesis (2016) investigated proximate influences to explain who tree swallows are undergoing such a fast-paced range expansion by focusing on aggression and stress hormones.

Kristen Content (MS 2017) focused on how stress hormones might dictate how individual tree swallows mediate aggression. She found high consistency in aggressive behavior, high plasticity in baseline corticosterone and moderate consistency stress-induced corticosterone. However, no direct association between aggression and corticosterone. Kimberly Todd (Honors Thesis 2018) investigated interactions between aggression and stress-induced corticosterone on fitness. The results are complex and compelling.

Anthropogenic influences on the environment are salient stressors to birds and other wildlife. Taylor Fulk (MS 2020) investigated how parental personality can influence whether offspring experience the expected negative effects of noise pollution. The fascinating result was that babies suffer from noise – unless they are reared by bold and aggressive mothers. Could we humans be selection for bolder wildlife?

Currently, we are working understanding the fitness consequences of assortative mating for personality in tree swallows.

I am also interested in how personality influences maternal effects. Using tree swallows, Alex Bentz (MS 2016) found that females breeding in high density environments are more aggressive and deposit more androgens in egg yolks. She showed with an elegant experimental design that those yolk androgens have both short- and long-term effects on offspring behavior and growth (Bentz et al. 2013).