The fundamental requirements that birds have are the same as other pests, for example food, water and harborage. Many food processing facilities offer all three in abundance as well as other factors that can attract birds, including:
Of grain, flour or other ingredients from the roof-top all the way down to surrounding grounds
Such as grain elevators or towering buildings that naturally appeal to cliff-dwelling birds like pigeons
With good exposures for flocking birds to find sun or shade
