Although participation in citizen science can improve cognitive and affective learning outcomes, many citizen science projects exhibit low retention rates. By gaining an understanding of forms of engagement, reasons for ongoing participation, and the impact of project design on participant motivation and engagement, we can help keep people involved in such projects. We address these issues by investigating motivational drivers and forms of engagement among volunteers in an ecological citizen science project. Our mixed-method approach involved interviews conducted with 26 core participants and questionnaires completed by 89 participants. Our analyses reveal an array of motivational drivers and various forms of engagement. While seeking to contribute to nature conservation was an important motivation for joining the project, the primary driver for ongoing participation was learning through social interactions. Moreover, the citizen science project design influenced participants' motivation and engagement.