Abstract: Biosphere Reserves (BRs), designated under UNESCO′s Man and the Biosphere (MAB) Programme, are recognized as crucial areas for biodiversity conservation. However, their actual contribution to bird protection on a global scale has not been systematically evaluated. This study utilizes global bird species distribution data from BirdLife International and the Handbook of the Birds of the World, along with boundary information of 759 BRs worldwide up to 2025. Using R language for spatial overlay analysis, it quantifies the coverage extent of BRs over terrestrial and marine bird distributions. The findings indicate that BRs provide extensive coverage for birds globally. Out of 10957 bird species, 8709 species (79%) have ranges overlapping with at least one BR. Notably, for 1, 901 fully migratory species, the coverage is particularly significant, with 1, 848 species (97%) appearing within BRs. In contrast, the coverage rate for globally threatened species (n=1372) is lower, with only 797 species (58%) overlapping with BRs. Among the 194 fully migratory threatened species, 174 species (90%) are covered by BRs. These results suggest that while BRs play a pivotal role in bird conservation, their protective effectiveness varies significantly among different threat levels. There is marked spatial heterogeneity in coverage patterns. At the continental level, Europe has the highest coverage of bird species (96%), followed by South America (92%) and North America (91%). The average continental coverage is 68%. On the oceanic scale, the Atlantic Ocean has the highest coverage (81%), followed by the Pacific (57%), with no coverage observed in the Southern Ocean. The average transoceanic coverage is 48%. According to the IUCN Red List, among the assessed 10957 bird species, 1372 are considered threatened, including 194 fully migratory endangered species. BRs cover 797 threatened species, representing 58% of the total. The coverage rate is notably higher for migratory threatened species: 174 out of 194 species (90%) are found within BRs. The average coverage rate for threatened birds in terrestrial and marine BRs is 54% and 60%, respectively. This method was further validated through case studies of regions where 34 BRs in China are located. The estimated number of species within each reserve, based on the global bird distribution map, ranged from 35 to 617 species (mean=302). Compared with published field survey data, the difference in species numbers ranged from 0 to 270 species (mean difference=84), but the two sets of data showed a significant correlation (Pearson′s r=0.56, P < 0.001). This suggests that while the global bird distribution map is suitable for large-scale assessments, it may overestimate the actual species richness of individual reserves due to resolution limitations and classification system differences. Overall, this study provides the first quantitative evidence on a global scale, demonstrating that BRs make an irreplaceable contribution to the protection of birds, especially migratory ones. However, their coverage of threatened species remains inadequate. It is recommended that the forthcoming MAB strategy and action plan (from 2026 onwards) prioritize systematic biodiversity monitoring, standardized and open species listing, and integration of multiple data sources. Strengthening data availability and methodological consistency will enhance the accuracy of conservation effectiveness evaluations and reinforce the role of BRs in global bird conservation.