1.The assessment of the effects of wind farms on bird populations is commonly based on collision fatality records. This could undervalue the effect of wind farms on small-sized birds. We evaluate the effect of wind turbines on occurrence, abundance and population trends of a threatened small passerine species, the Dupont's lark Chersophilus duponti. To our knowledge, this is one of the first studies addressing the effect of wind farms on population trends using time series data from multiple wind farms. 2.We estimated population trends by fitting a switching linear trend model with the software TRIM (Trend & Indices for Monitoring data). We used multiannual data surveys of five populations in the presence of wind farms and nine in their absence (2008–2016 period). Furthermore, we fitted a logistic and a negative binomial regression model to test the effect of wind farm proximity on species occurrence and abundance in 2016, respectively. We incorporated local connectivity and habitat availability estimates in both models as predictors. 3.Results showed a negative trend overall, but that was significantly more regressive in the presence of wind farms: 21.0% versus 5.8% average annual decline in the absence of wind farms. 4.Dupont's lark occurrence and abundance in 2016 were negatively affected by measures of population isolation and positively affected by the distance to wind farms. 5.These results highlight the negative effect of isolation and wind farm proximity on Dupont's lark population parameters. Taking into account the metapopulation structure exhibited by the species in the study area, this work established a 4.5 km threshold distance from wind farms, beyond which Dupont's lark populations should be unaffected. 6.Synthesis and applications. This work highlights the negative impact of wind farms on small-sized birds and provides a 4.5 km threshold distance that should be taken into account in the design of future wind energy projects. Moreover, we suggest an analytical approach based on population trends, species abundance and occurrence variation in relation to wind farms, useful for the assessment of wind farm impacts on small-sized birds.