The Hidden Forms And Functions Of Courtship In The Brown-Headed Cowbird (molothrus Ater)

Reproductive fitness is the result of complex interacting processes, however our understanding of reproduction is often limited to a few, static male traits. While conspicuous male traits are very well studied, female behavior has received far less attention. Furthermore, conspicuous male traits often fail to predict reproductive success, suggest that there are other important aspects of sexual behavior, however what these factors are or how they interact remains largely unknown. Brown-headed cowbirds (Molothrus ater) breed readily in captivity and their copulatory behavior can be evoked under carefully controlled experimental conditions. By pairing many years of behavioral observations with careful analysis and quantification of behavior, I identified several mechanisms guiding courtship and reproduction. Female copulation is directly evoked by male song, and the strength of the copulatory display reflects signal strength. Interestingly, the copulatory display is mediated by the variable behavioral state of the female, suggesting that song alone is insufficient to elicit copulation. Flocks also display measurable cohesion in the timing of their behavior, transitioning as a group between singing to males and singing to females, and the strength of this group cohesion predicts reproductive success for both individuals and the group as a whole. This work shows that reproductive fitness is far richer than just the quality of male signals and provides a platform to understand the rich complexity of animal courtship.