Bird droppings are not only unsightly, but their high nutrient content provides an excellent growth medium for harmful organisms that can cause two primary illnesses in humans: cryptococcosis, which is a fatal fungal disease, and histoplasmosis, which is an infection transmitted by airborne spores that generally affects the lungs but may spread to other organs or tissues—infants and children are especially susceptible to these illnesses. Bird droppings accumulated on wood and other areas, such as fence posts and railings, should be removed immediately. Removing bird droppings from wood is a simple as scraping up the excrement with a putty knife and spraying the area with water and bleach.
Put on the gloves, goggles and mask. Keep kids and dogs away from the area.
Scrape the fresh and dried excrement into a pile, and push that pile into old newspaper or into a trash can for immediate disposal.
Spray the wood using a high-pressure nozzle and garden hose. Wash away as much of the remaining residue from the droppings as possible.
Spray the wood with bleach (in the spray bottle). You shouldn't have to saturate the area at this point, but you do want to kill the possibility of bacterial growth. Bleach will do the job.
Spray down the wood one more time using the garden hose and high-pressure nozzle.