I don't know about anywhere else, but in Lansing most bird poop is white, usually with a dark center. I don't think birds eat very much that is this white (mostly seeds and insects), so why is it white? Thank you, D.W.
Birds are always on the move and don't have time to stop for potty breaks. That's why flying birds can't be house broken because as soon as the need arises instinct tells them to get rid of the useless weight to be a more efficient flyer.
But why is their poop white? Songbirds can't urinate like mammals because they don't have a bladder. Their kidneys extract nitrogenous wastes from the bloodstream, and instead of excreting it as urea dissolved in urine as we do, they excrete it in the form of uric acid.
Uric acid emerges as a white paste often ejected with the waste from food which is the darker stuff in the center. Both waste products come out together because birds have a single opening called a cloaca, which they use for waste disposal and reproduction.
And finally, if you think you've been the target of a bird bomber, keep in mind that a lot of people considered it good luck!