•Impacts of the EU’s CAP instruments, production intensity and landscape characteristics on farmland birds were analysed.•Areas with high direct payment support were negatively associated with farmland bird diversity.•Farmland bird diversity was highest in a diversely cropped farmland with <25 % of woody vegetation.•Open grasslands in Natura 2000 sites with low stocking density supported the highest diversity of grassland specialists.•AES and “Greening” measures had a weak effect on bird diversity, possibly due to ineffective implementation. The paper investigates the relative influence of landscape characteristics, production intensity and the EU’s Common agricultural policy interventions on the diversity of farmland birds. For this purpose, data from the Farmland Bird Monitoring Scheme in Slovenia and high spatial resolution data from the national agricultural databases in the period 2008–2019 were analysed with the Boosted Regression Trees (BRT). The diversity of farmland birds was found to be highest in open, diversely cropped and extensively to moderately intensively managed landscapes in Natura 2000 sites where farm holdings were allocated a low average amount of both direct payments and payments for agri-environmental measures (AEM) and organic farming (OF). Furthermore, the highest diversity of the subgroup of grassland specialists was associated with very open and extensively managed grassland landscapes with low stocking density (<0.7 LU/ha). By contrast, the diversity of habitat generalists was highest in heterogeneous landscapes with a high diversity of land-use types, measured at the broader spatial scale. Areas with a higher allocation of direct payments and payments for AEM and OF were associated with lower farmland bird diversity, whereas high diversity was found in Natura 2000 sites and in some areas with natural constraints (LFA). Agri-environmental measures and the “Greening” measures had a negligible relative influence on bird diversity, possibly due to ineffective implementation and low uptake by beneficiaries. The intensification of production, particularly in the beef and dairy sectors, which has been supported by the Common agricultural policy direct payments, and forest succession in marginal areas were identified as the potential key drivers of the recent farmland biodiversity loss in Slovenia. The future CAP income support schemes should be redesigned to ensure at least neutral if not positive overall effects on farmland biodiversity by gradual phasing-out of references to (historic) production levels, increased conditionality and more effective voluntary agri-environmental measures.