Find the nests. This should be job No. 1 when solving widespread bird activity on structures.
Look for concentrated droppings, and then inspect up above. Birds set up many stop points in and out of nesting areas. Droppings lead the way. If no nests or eggs are found, treat these areas with medium-pressure deterrents.
If nests are found, remove them and prevent bird-nest reclaiming instincts by using a high-pressure barrier, following a diligent, bird-specific cleaner. Your customer can then address future activity with less investment, as the heavy reproduction source at the property — the nest — has been addressed.