I always wondered how bird shit could have the white and black bits seperate myself...
From Yahoo Answers:
The Biology of Bird Poop:
Birds, like many reptiles, do not secrete nitrogenous wastes in the form of urea CH4ON2, like mammals do. (Urea is what is in human urine.)
Instead, birds secrete uric acid C5H4O3N4, which in insoluble in water and looks like a white paste. Many reptiles also secrete uric acid, because it conserves water better than urea. It also eliminates the need for a heavy, water-filled bladder. The latter is the important element for birds, which need to be as light as possible, for flight.
Birds have a single exit opening, the cloaca, again unlike us. This opening is used for both for excretion and reproduction. When they excrete waste, they combine the uric acid crystal-paste (the white stuff) with the dark fecal waste from their intestine.
