Cooperation is a complex behavior in which individuals act in ways that increase the fitness of others. Individuals vary in cooperative tendency, even when raised under similar developmental conditions. This individual variation remains an overlooked factor that could promote cooperation and explain why cooperation occurs, even among unrelated individuals.
My dissertation research investigates the proximate mechanisms that influence individual variation in cooperative behavior. I examine how differences in early life development, physiology, and personality relate to variation in adult cooperative and aggressive behavior.
The brown-headed nuthatch (Sitta pusilla) is an excellent species in which to study individual variation in cooperative behavior. Brown-headed nuthatches are facultative cooperative breeders found in the southeastern United States. In our study population at Tall Timbers Research Station and Land Conservancy, which has been monitored for over 10 years by Jim Cox, approximately 30% of breeding pairs are assisted by helpers and approximately 25% of first year males assist breeders raise offspring. Extra-pair paternity is relatively high and helpers are sometimes unrelated to the breeders they assist.
Jessica Cusick measuring a brown-headed nuthatch egg at Tall Timbers Research Station. Photo Credit: TTRS
Brown-headed nuthatch attacks a red-headed woodpecker taxidermy model. This individual received the highest aggression score for making contact with the model. Photo Credit: Jessica Cusick
Brown-headed nuthatches care for offspring in cavity.
Photo credit: Tara Tanaka
Two chicks are individually marked with non-toxic prism markers. I film the fledging behavior of these chicks and record the order in which they fledge and how long it takes each chick to leave the nest. I am interested in how variation in physiological mechanisms including size and stress response relate to variation in fledging behavior. Photo Credit: Jessica Cusick