The method relies on birds being startled by the strong contrast between the ambient light and the laser beam. During low light conditions this technique is very selective and can be tuned to frequencies and wavelengths that individual bird species don't like, but at night the light beam is visible over a large distance and can cause widespread (non-species specific) disturbance.
The method depends on birds being alarmed by the stark difference between the surrounding light and the laser beam. Under dim lighting conditions, this approach is highly targeted and can be adjusted to frequencies and wavelengths that certain bird species dislike, but at night, the light beam becomes visible over a considerable distance and may cause widespread (non-specific) disruption.