According to About Pet Birds, the best way to clean bird dropping stains from clothes is to remove the solid waste first by scraping it off before wetting the stain. After removing the solid waste, pre-treat the spot as a regular stain, and then wash as usual. Make sure to check the stain after pre-treating but before you put the clothes into the dryer, because heat sets stains.
Once the bird droppings are dry, use a paper towel to remove the debris in as close to one piece as possible. If there is any dry mess left behind, use something hard and narrow, such as the edge of a credit card, to scrape away the remnants. If there is a leftover dropping stain, use a wet cloth to soak the area until it is less visible. According to Good Housekeeping, a laundry product containing enzymes helps break down the biological components of the bird droppings, minimizing the appearance of the stain at the pre-treat stage. If the stain is still there after pre-treating, try using hydrogen peroxide in a diluted solution or a drop of ammonia to loosen the stain further. Rinse the stain thoroughly with water after pre-treating but before washing the clothing.