Science hobbyists engage in self-directed, free-choice science learning and many have considerable expertise in their hobby area. This study focused on astronomy and birding hobbyists and examined how they used organizations to support their hobby engagement. Interviews were conducted with 58 amateur astronomers and 49 birders from the midwestern and southeastern United States. A learning ecology framework was used to map the community contexts with which the hobbyists acted. Results indicated seven contexts that supported the participants' hobby involvement over time: home, K-12 schools, universities, informal learning institutions, hobby clubs, conferences, and community organizations. Three themes emerged that described how hobbyists interacted with organizations in their communities: (1) organizations provided multiple points of entrance into the science-learning ecosystem, (2) organizations acted as catalysts to facilitate a hobbyist's development in their hobby, and (3) the relationship between hobbyists and organizations they used for learning eventually became bidirectional. Results showed that both astronomy and birding hobbyists used science-learning organizations to meet their hobby-related learning goals. Most hobbyists in the sample (90% astronomers, 78% birders) also engaged in outreach and shared their hobby with members of their community. Patterns of interaction of the astronomy and birding hobbyists within the seven contexts are discussed.