I have cleaned off berry juice droppings from the house exterior, the patio, patio furniture and have revived stunned cedar waxwings that ran into the glass doors..I know the problem.
We have doves that "graze" in our backyard...they bolt in panic whenever the local redtail hawk cruises by, and we must get our back windows (virtually the entire rear of our home is either window or slider) slammed into, leaving the feathery silhouette, 3 or 4 times a month.