The present disclosure relates to wind turbine blades, devices and methods for reducing vibrations in wind turbines, particularly during installation. In an aspect, a device for mitigating vibrations of a blade of a wind turbine during standstill is provided. The device comprises a flexible base having a first connection area and a second connection area, the first connection area being configured to be attached to the second connection area to form a removable attachment. The device further comprises one or more airflow modifying elements attached to the flexible base. The flexible base is configured to fit around a portion of the rotor blade such that the removable attachment is positioned substantially at a leading edge of the blade. The present disclosure further relates to methods for mitigating vibrations in a parked wind turbine blade and to sleeves for wrapping around a portion of a wind turbine blade.