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Understanding the ecological drivers of abundance is essential for assessing how environmental changes affect distributions. Gaining deeper insights into these drivers can also help explain global biodiversity patterns. Birds offer an exceptional opportunity to explore these patterns given their extensive spatial data coverage. In this study we used abundance data for 2,182 bird species to identify main drivers of intraspecific variation in abundance. We explored the relative impact of macroclimatic, biotic and anthropogenic drivers and distance to range centroid. We then applied phylogenetic comparative analyses to assess how morphological, geographical and ecological traits mediate species' responses to these drivers. We found that macroclimatic drivers were the most important predictors of abundance. We further found support for the abundant centre hypothesis. Trait analyses reveal that range size, hand-wing index and migratory behaviour are good predictors of how species respond to various environmental gradients. Our findings highlight a prominent role of the climate in explaining relative abundances of birds, but also that species traits can explain part of the complexity of abundance distributions. To this end, our results can help better predict how different species might respond to ongoing environmental changes.