Over the recent decades, Europe has experienced a significant decline in common bird species, particularly farmland species, due to anthropic pressures like agricultural intensification. Protected areas, such as the Écrins National Park in France, play a crucial role in mitigating these impacts. In this study, we utilized an opportunistic presence-only dataset of passerine occurrences to evaluate the impact of protected areas on passerine trends. The data, gathered by trained rangers from Écrins National Park, were used for spatio-temporal modeling to assess the relative abundance of 76 passerine species on a regular grid, with aggregated occurrences per spatio-temporal cell serving as a proxy for sampling effort. The model demonstrated good calibration for most species, with AUC values from different cross-validation schemes exceeding 0.8 in most cases. The model also effectively distinguished habitat preferences and migratory status. Additionally, we compared trends in relative abundance over 2001–-2019 in the Écrins National Park with the trends in abundance across France using the French Breeding Bird Survey (STOC program) for 59 common species. Our analysis revealed that forest specialist species benefited the most from protected areas, farmland species decreased more slowly, and high-elevation specialist species generally decreased. Though, some results should be interpreted with care since our assumption of a homogeneous reporting rate across target group species may be too strong for some very common species. Our findings illustrate that the high spatio-temporal resolution provided by opportunistic presence-only data offers valuable insights into biological phenomena and their trends while reducing the need for other data sources to determine sampling effort proxies. Similar datasets from other protected areas could serve as powerful tools for assessing the effectiveness of conservation policies.