Colonial seabirds that nest in stable, predictable environments tend to breed with the same mate for consecutive seasons. In some of these populations, mate retention has shown to be correlated with previous reproductive success. Caspian Terns (Sterna caspia) were observed in northeastern Lake Michigan at several colony sites that vary in stability because of fluctuating water levels. Objectives of my study were to determine if (1) individuals tend to keep the same mate for consecutive breeding attempts, (2) mate retention is influenced by previous reproductive success or inter-year nest site stability, and (3) reproductive success is affected by mate change. Only 25% of the original pairs bred together for consecutive seasons, mate retention was independent of reproductive success the previous year but not of inter-year nest site stability, and I found no significant advantage in retaining the same mate for consecutive seasons. These results indicate that factors other than previous reproductive success (e.g., habitat stability) influence mate selection and retention in this population of Caspian Terns. Caution should be exercised in assuming that the relationship between mate retention and previous reproductive success holds for other species of colonial seabirds.