This dataset accompanies the article: Key structural attributes of Mediterranean reforestations for avian diversity conservation: comparisons with mature forests, and provides all the necessary information to replicate the analyses on how bird diversity relates to structure in mature and reforested forests in central Spain. Data was collected from 53 forest plots from mature and reforested forests. In each plot, we characterized forest structure and conducted passive acoustic monitoring for seven consecutive days to assess bird richness, community composition, and functional group structure. The dataset is organized into the following supplementary tables: Table S1 – Forest site descriptors: Includes general and environmental data per plot such as geographic coordinates, elevation, climate (mean annual temperature and precipitation), dominant tree species, forest type (mature or reforested), slope, aspect, lithology, estimated stand age, and presence of deadwood (standing and lying) and stumps. Table S2 – Forest structural attributes: Summarizes plot-level forest structure including average tree height, mean and coefficient of variation of DBH (diameter at breast height), average height-to-DBH ratio, tree density (individuals per hectare), canopy cover, shrub cover, and deadwood volume. Only trees with DBH > 7.5 cm were included in calculations. Table S3 – BirdNET detection thresholds: Contains species-specific logistic regression parameters (intercept, slope, and 95% confidence cutoff) used to filter automated song detections and minimize false positives. Table S4 – Bird functional traits: Provides ecological trait data per species, including habitat affinity, migratory behavior, trophic niche, and nesting strategy. Traits were compiled from the AVONET database (Tobias et al., 2022) and SEO/BirdLife species accounts. Table S5 – Bird song activity matrix: A species-by-site matrix based on standardized vocal activity (song frequency per hour), used to quantify species composition and functional guild representation.