Adult sex ratio (ASR, the proportion of adult males in the adult population) and operational sex ratio (OSR, the proportion of sexually active males in the mating pool) are fundamental properties of breeding populations and they are often linked to mating systems and sexual selection. However, ASR and OSR emerge via different routes in a population and may exhibit different temporal patterns. Here, we use data from a well-monitored polygamous snowy plover Charadrius nivosus population sampled over 3 consecutive breeding seasons to investigate whether temporal changes in ASR relate to changes in OSR. We found that snowy plovers exhibited male-biased ASR and OSR. Consistent with theoretical expectations, OSR was more variable than ASR. However, there was no consistent relationship between OSR and ASR: in only 1 of the 3 study years we found a weak positive relationship (r = 0.22). The lack of association was corroborated by time series analyses and sensitivity tests. Our work therefore suggests that ASR and OSR exhibit different temporal patterns in a polygamous population, and we call for further theoretical and empirical studies that analyze their relationship across a range of different breeding systems.