- Citizen science is a growing phenomenon across many branches of environmental science facilitating both increased science literacy and the collection of highly rigorous, longitudinal data. Understanding the motivations of adults to join and remain active in citizen science programs is important as the diversity and abundance of opportunities for public participation in science grow. We conducted a mixed-methods study of newly recruited and “seasoned” (1 year plus) participants in the Coastal Observation and Seabird Survey Team, a hands-on, environmental citizen science program focused on adult coastal residents, to explore the degree to which engagement, measured as time in the program, influenced motivation. We used constructs of functionalism, person-object theory of interest, and activity theoretic approaches to situational identity to deconstruct motivation into three interacting components: objects of interest, actions directed toward those objects, and situated senses of self. Newly recruited participants came with a strong interest in being outside on the beach and learning about birds and saw themselves as data collectors defined in part by their birding and degree/job-based credentials and their social relationships. By contrast, seasoned participants aligned their interests and situational identity more directly with the program, calling out the importance of program data and results, elevating science-based actions such as monitoring over learning, intensifying their desire to contribute to science, subjugating individual attributes in favor of their science identity, and increasing their sense of self-worth attached to the project. Our results suggest that hands-on, environmental citizen science programs focused on adults should shape their data collector roles and projects around context-specific motivations including senses of place and biodiversity, support both the altruistic and self-interest needs of participants, and combine rigorous science experience with social interaction.