A closer look
If you've ever had your freshly washed car violently desecrated by a pigeon, you know exactly how terribly efficient avian biology is. Birds are desperately obsessed with weight reduction for flight, so they evolutionarily ditched the heavy urinary bladder entirely. Instead of casually holding liquid urine, their kidneys extract nitrogenous waste and aggressively concentrate it into a dense uric acid. This gets unceremoniously mixed with their feces in the cloaca, resulting in that highly corrosive, dazzlingly white paste that miraculously always manages to perfectly hit your windshield.
