The Real Reason Bird Poop Is White
It's a good question. Whether from a human or canine or some other creature, most poop is plainly not white. Why is bird poop so special? If you spend enough time cleaning it off your car (or, unlucky you, yourself), you have to at least wonder. No less a source than the venerable Encyclopedia Britannica has given an answer: It isn't white at all. Wait, what?
As it happens, birds don't have the same waste management set-up as most other animals. Birds have one exit, the cloaca, that they use for laying eggs, pooping, peeing, and having sex (via Live Science). Both male and female birds have a cloaca instead of a penis or vagina, though only female birds produce eggs — male birds produce sperm from their cloaca instead. (Birds have sex by rubbing their swollen cloacas together.) All of these different substances get quite a stew going inside the cloaca. But how does that make bird droppings appear white?
It's not (just) poop
When a bird relieves itself, it's really relieving itself. Birds, according to Britannica, pee and poop at the same time. The poop is the dark part at the center of bird droppings, while the white part is in fact the bird's urine. Bird pee, unlike the urine of most other animals, is converted to uric acid before discharge, which both conserves water and creates a white paste that seems impossible to get off your windshield. That's not just your imagination — according to the National Audubon Society, bird droppings are hard to clean because uric acid doesn't dissolve in water easily.
Two more notes (calling them "fun facts" might be pushing it): Though all birds have cloacas, not all of them pee and poo simultaneously — ostriches pee first, for instance, and dinosaurs may have done the same thing. Not exactly related, but birds see color (per The Spruce). And according to one study, red cars are more likely to be hit by bird droppings than green cars. Just in case that affects your purchase.