Recreation specialization postulates that people progress through a career when engaging in a leisure activity. This has been studied by cross-sectional and few panel studies, but both methods have some shortcomings. Here, I studied German birdwatchers from the 16 federal states of Germany by employing the propensity score matching method. Data were collected using the online research tool SoSciSurvey between 14 February 2020 and 15 June 2020 include study population, sampling, data collection, and analysis in short. Three career stages of the same size were defined according to birdwatching experience in years. Then, respondents were matched according to age, gender, federal state, and educational level but differed in their leisure career stages by propensity score matching, thus birders of the same age, gender, educational level, and federal state were identified that differed in their birding experience in years. Stage 1 was birders with ≤10 years of birding, stage 2 with 11–34, and stage 3 with ≥35 years. This led to 177 pairs in the stage 1–2 comparison and 113 pairs in the group 2–2 comparison. The recreation specialization construct based on the dimensions behavior, skill, and commitment was applied. There was a highly significant effect concerning skill/knowledge and behavior between stage 1 and 2 (p < .001 for both). However, no differences were found concerning personal and behavioral commitment (p > .5). Skill/knowledge increased again between stage 2 and 3 (F = 4.554, df = 112, p = .035), no significant changes concerning the other three dimensions behavior, personal, and behavioral commitments were found (p > .2). The study provides evidence for a career development in leisure.