Robop bird prevention systems, generally speaking, will not work if the birds are sitting on eggs or if the nest contains young chicks. This is because birds would rather die than risk their young. For example in the UK, gulls tend to select a nesting site during February and March, build a nest in April and then vacate that when their young leave the nest in July or early August. This makes the period August to February the best time to deploy a Robop bird control system.
Note also that birds are very much creatures of habit. If they find a good spot to roost or nest they will return to the same spot day in day out, year in year out, unless something happens, such as Robop appearing, that forces a change.