Protected areas are one of the most widespread and accepted conservation interventions, yet population trends of species within protected areas are rarely compared with regional trends to gain insight into their effectiveness. Here, we leverage two long-term community science datasets, finding mixed effects of protected areas on long-term bird population trends. We analysed 31 years of bird transect data recorded by community volunteers across all major habitats of Stanford University's Jasper Ridge Biological Preserve to determine the population trends for a sample of 66 species. We found that nearly a third of species experienced long-term declines, and on average, species declined by 12%. Further, we averaged species trends by conservation status and key life history attributes to identify correlates and possible drivers of these trends. Observed increases in some cavity-nesters and declines of scrub-associated species suggest that long-term fire suppression may be a key driver, reshaping bird communities through changes in forest and chaparral structure and composition. Additionally, we compared our results with those of the North American Breeding Bird Survey's Central California Coast region (n = 55 species) to place Jasper Ridge in a broader context. Most species experienced similar directional population trends inside and outside of the preserve and only eight species (14.5%) did better inside this small protected area. Therefore, we must identify relevant management strategies for declining populations and explicitly consider how existing protected areas target and manage each species. Further, this analysis underlines the importance of local and national community science for revealing long-term bird population trends. [link to publication]