Why is bird poop white?

If dead red blood cells make our poop brown, what makes bird poop white? (unless of course they are pooping on a white car in which case they poop black!)

It can also be a nasty purple color when they eat the damn mulberrys.

Short, simple and slightly inaccurate answer is that bird shit is white because it isn’t just shit, it’s a mixture of shit and piss. Bird piss is white, hence the pile of white stuff on bird shit is actually dried piss.

Longer and more accurate answer. Birdies come from eggs. A chick in an egg can’t produce liquod waste because that would rapidly diffuse through the entire egg and poison the chick. As a solution bird kidneys don’t produce liquid urea waste as mammals do. Instead they convert the urea into uric acid. Uric acid is a white crystalline solid. That explains what the white stuff is.

Add to this that birds don’t have an anus and a separate penis/vagina as in most mammals. Instead the kidneys and bowel both void through a common opening known as a cloaca. So when a bird takes a crap it also releases the waste from the kidneys. As a result bird shit can be almost any colour at all, but it will almost always have a little pile of white crystals lying on top.

Source: http://www.heptune.com/poop.html

What about Canada geese? Their all-too-familiar turds are sort of dark green, which I suppose makes sense considering that they eat grass. But the turds are kind of watery and don’t seem to include any paste.

Low protein diet. Nitrogenous wastes such as urea and uric acid are primarily the result of the animal eating so much protein that it starts burning protein as food rather than using it as building material. Geese and other birds on a diet of low quality vegetable matter are often struggling to get enough protein, and so produce relatively little uric acid. Birds on a grain diet recieve adequate protein and so produce modest amounts of white crap. The shit of carnivores or seabirds has huge amounts of white crap all over it.

What Blake said; just to add this old joke (courtesy of Kurt Vonnegut):

Q. What’s the black stuff in the middle of bird shit?
A. That’s bird shit also.

OK, not that funny. Or even technically correct.