Dominance, Age, and Reproductive Success in a Complex Society: A Long-Term Study of the Mexican Jay

Observations of mate guarding by males and robbing of nest material by females suggest the hypothesis that dominance should be related to reproductive success in the Mexican Jay (Aphelocoma ultramarina). We analyzed the probability of successful reproduction in this plural-breeding, group-territorial species with respect to variation in social rank, sex, age, flock territory, and year. We examined the correlates of dominance rank at two stages of nesting, early (before and during laying) and late (after laying). The correlates of rank differed between the sexes and nesting stages. In the early or prelaying stage, success in getting a mate and initiating laying was correlated with rank in males but not in females, and with age in both females and males. In the late stage, given that a bird had a nest with eggs, fledging success was not significantly related to rank overall. In females, however, a significant interaction was found between rank and age such that top rank was associated with greater success in older but not younger females. These effects of dominance at two stages of the nesting cycle (i.e. before and after egg laying) are consistent with the mate-guarding behavior of males and the nest-robbing behavior of females during nesting.