The rapid development of wind energy may have negative effects on bird populations, including collisions with turbines, displacement due to disturbance or habitat loss, indirect effects of reduced breeding success and barrier effects. This challenging conservation issue has attracted a great deal of interest, but the noise generated by turbines has been largely overlooked. Here, we studied acoustic behaviour of Skylarks Alauda arvensis in relation to wind farm start‐up to assess whether a change in song parameters can indicate a deterioration in the acoustic environment. We recorded territorial males displaying close to operating and non‐operating turbines and at a control site without turbines. In the following breeding season, we undertook replications at the same sites, except that the non‐operating turbines were now in operation. We found that Skylarks displaying at the wind farm were affected by wind turbine noise. Males singing close to operating wind turbines sang higher‐frequency songs than males from a control site and those that displayed near non‐operating turbines. In addition, an upward frequency shift in songs was observed when non‐operating turbines started to operate in the consecutive season. We therefore conclude that the frequency shift observed did not result from turbine presence, but from the noise they started to generate. This shows that a change in song parameters may reliably and within a relatively short time indicate a significant deterioration of the acoustic environment as a consequence of wind farm start‐up. This may help conservation biologists to identify species and populations that are particularly susceptible to wind farm noise.