Fighting and assessment in the yellow-rumped cacique (Cacicus cela)

Summary I tested the prediction derived from game theory models that the intensity of aggressive interactions should reflect the value of the resource being contested and the disparity in fighting ability of the contestants. Females of the yellow-rumped cacique compete for nest sites and the material to build nests. Females competing for established nest sites engage in higher intensity interactions than those competing for sites in which building has not begun and against females robbing nest material (Fig. 1). For males, access to females is determined by dominance, which is positively correlated with weight. Comparably-sized males (Fig. 2) and those of similar rank (Fig. 3) engage in significantly more intense interactions than males that differ widely in size or rank.