About This Project

Bachman's sparrow is a beautiful songster once common to the American southeast. Males vary in how aggressively they defend their territory. Do mad dads produce more, healthier offspring, or is aggression costly? We will measure territory quality, aggressiveness, and hormones of territorial males and link these factors to the success of offspring. We aim to conserve Bachman's sparrow and better understand reproductive success in songbirds.

Ask the Scientists

What is the context of this research?

Why do individuals competing for resources vary so much in how hard they fight for them? If being very aggressive wins fights, then we should expect all males to fight hard when their resource is contested. Counter to this prediction, we see great variability in the vigor with which individual males respond when challenged (Mougeot et al 2003). One explanation for this variation is that individual males face tradeoffs between the benefits of securing the best territory, and the costs associated with heightened aggression (Class and Moore 2010). These costs may be physiological costs of increased hormone levels, energetic costs, or reduction in parental effort (Ketterson et al. 1992). Males vary in their ability to bear these costs, thus aggressiveness varies among males.

What is the significance of this project?

We are addressing a key question in behavioral ecology: what selective mechanisms maintain variation in behavior? We aim to establish Bachman’s sparrow as a model system to address this question, while also gaining information critical to the species' conservation. Bachman’s sparrow is listed as a conservation priority by conservation organizations and agencies throughout its range. Previous research has focused on natural history and demographics, leaving critical gaps in knowledge about social dynamics such as territorial behavior. These gaps in knowledge impede conservation efforts because understanding and predicting population dynamics cannot proceed without understanding the social factors that can underlie variation in reproductive success.

What are the goals of the project?

We will mark 40 adult male sparrows for individual identification, sample blood for DNA and hormone analysis, and measure male quality (mass, tarsus, wing cord, and body condition score). We will measure each male’s territory size and quality using published methods for this species. For each male we will locate and monitor nests, count and weigh nestlings, take blood samples for paternity analysis, and determine the number of young fledged from each nest. We will quantify each subject’s aggressiveness in response to a simulated rival utilizing song playbacks and a Bachman’s sparrow replica placed within the male’s territory. We will analyze these data to determine how aggressiveness relates to habitat quality and reproductive success.