Sperm competition is prevalent in animals, and many adaptations have evolved to reduce its risk. Males can reduce the risk of sperm competition by using public information when interacting with potential mates. Specifically, males can reduce sperm competition by avoiding females already affiliated with rival males. We tested this hypothesis in a population of wild northern map turtles (Graptemys geographica), a gregarious species with seemingly prevalent sperm competition. We used 3D‐printed decoys and underwater videography to record the response of free‐ranging males to female decoys affiliated or not with rivals. More visits were made by males to female decoys when rivals were present, suggesting a form of eavesdropping during mate selection. Males were more likely to interact with the female decoy, however, when rivals were absent, suggesting that they behave to reduce sperm competition. Moreover, the types of interactions differed between the accompanied and the unaccompanied female decoys, indicating an audience effect during male–female interactions. Finally, males interacted more with the male decoys than with the female decoys in the treatment with rivals, indicating a yet unclear form of male–male interaction. Collectively, our results suggest that free‐ranging male northern map turtles use public information for mate selection and to reduce sperm competition.