Personality & Fitness in Bluebirds & Tree Swallows

The focus of my post doctoral research was to understand the evolutionary significance of personalities in eastern bluebirds. 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. In these species, I am studying whether personality affects mate-choice decisions, female promiscuity, and competition for breeding resources between individuals of the same sex. 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’ current research focuses on whether interspecific competition between tree swallows and bluebirds influences the relationship between parental personality, behavioral syndromes, assortative mating and reproductive success in Eastern bluebirds. 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.

I am also interested in how personality influences maternal effects. Using tree swallows, my former MS student, Alex Bentz 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).