Bird Droppings Replace Liquid Urine

Birds have no bladder, so they do not store or release liquid urine the way mammals do. Over time, they evolved to skip liquid pee altogether, saving weight that would otherwise go to carrying extra water. Instead, they eliminate their waste all at once in the form of a chalky white paste that people often see on sidewalks, cars, and windows. Each dropping combines what would be urine and feces into a single lightweight package.

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