Biology graduate student Jessica Krippel spent the summer on campus observing, catching, measuring, attaching identification bands to and taking blood samples from dozens of song sparrow couples and, under their anxious, protective watch, their chicks. The work is part of a study of songbird personality traits – primarily aggression among males – and the connection to reproductive success.
Although songbirds are primarily socially monogamous, nesting and raising children with one mate, they are not always “genetically monogamous” and engage in “extra-pair copulation,” said Krippel. (For nonscientists, that’s the biologically correct way of saying the birds have affairs.) Typically, more than 15 percent of sparrow offspring are “extra-pair young,” she said. Krippel and Jeremy Hyman, associate professor of biology, specifically designed the study to examine if more-aggressive male song sparrows have more offspring.
“One possibility is that aggressive males do better in both regards – they get more EPCs (extra-pair copulations) and also protect their paternity at home,” said Hyman. “Another possibility is that they gain more EPCs from neighboring females, but while they are out, their females engage in EPCs with other neighboring males.”
To study the question, Krippel spent the approximately four-month mating season mapping 50 songbird territories, finding nests, catching adults and babies, and taking 360 blood samples to analyze paternity. She came to know some birds better than others, such as “The Patriot,” named for his red, white and blue bands; “The Slacker,” who was late to settle a territory and mate; and “Stumpy,” who appeared to have survived something that damaged his tail feathers.
In addition, Krippel and Hyman conducted tests to measure aggression by determining to what degree a male songbird sparrow would defend his territory. Song sparrow territories on campus are about 20 yards apart, said Krippel. When defending them, males will sing and counter-sing, moving closer together. If the situation escalates, the birds grapple and peck at each other. Krippel has witnessed this level of combat only twice at Western Carolina.
Supporting the research project is a $500 grant from the High Country Audubon Society and a $500 matching gift from bird enthusiasts Bill and Peg Steiner. In addition, Krippel has received two graduate assistantships from WCU and assistance from undergraduate students Nicole Salzmann and Morgan Simril. Salzmann and Simril helped watch the fine, specially designed nets and traps used to catch the birds without harming them that must be monitored at all times.
After analyzing the songbirds’ DNA through work with Barbara Ballentine, assistant professor of evolution and behavioral ecology, Krippel hopes to share the results of the research not only in her thesis but also with presentations for the High Country Audubon Society, a behavioral ecology meeting and WCU’s graduate research symposium. “My study will help to clarify if there is an evolutionary role of animal personality,” said Krippel. “Any trait, whether it be physical or behavioral, that affects the reproductive success of a species has evolutionary significance.”