Robust Fall Social Displays Predict Spring Reproductive Behavior in Brown-Headed Cowbirds (Molothrus ater ater)



Gregory M. Kohn, Department of Psychological and Brain Sciences, Indiana University, 1101 E.10th St., Bloomington, IN 47405, USA.



The ability to engage others in close proximity may be an essential component of social life and shapes the development of social skills. Variation in the willingness to initiate and sustain close interaction with conspecifics is known as sociability. The Brown-headed Cowbird (Molothrus ater) uses an affiliative display called the head-down to bring individuals into close proximity. During fall 2009, we manipulated a large flock of cowbirds in a fission–fusion perturbation and recorded the frequency of head-downs and social approaches. During the fission–fusion perturbation, the rate of head-downs remained both correlated and repeatable across perturbations. In spring 2010, we separated individuals into three aviaries, a high, intermediate, and low aviary, based on the frequency of head-down displays they initiated during the previous fall 2009. When breeding, males in the high flock produced a higher number of songs within counter-singing matches, and females laid more eggs in comparison with the other aviaries. These findings suggest that head-down displays performed outside the breeding season may contribute to the development and maintenance of reproductive competence by providing intimate social interactions with others.