Audio bird deterrents like bird distress sound makers, canons and screech owls can be successful in deterring birds when combined with visual and/or taste repellents.
TIMING, PERSISTENCE, ORGANIZATION and DIVERSITY are critical for using these products. Timing is critical as birds are more apt to leave a briefly occupied site rather than an established roost. Appoint one person to organize and implement a harassment campaign commencing one hour before sunset and/or dawn using a diverse product mix. Effecting a dramatic change to the roosting area will often persuade birds to disperse. The obvious tactics include elimination of a food source, shelter and water. Remove nesting materials, thin/trim trees.
A wide array of bird scare products is available. However, no single product stands alone; a combination of deterrents must be used with repeated reinforcement as necessary.