Omnivores' effluent = brownish, herbivores (cow-pats) = brownish/green, but why white for birds?
Bird poo is white because of the amount of crystalline urea it contains.
Urea is a by-product of normal digestive processes which ground-dwelling creatures get rid of dissolved in their urine. (The name's a bit of a hint
)
Water weighs 1000kg per cubic metre, so if you want to fly under your own power you don't want to be carrying too much of it. As an evolutionary modification therefore, birds run their metabolism pretty dry, and don't have a bladder. There simply isn't enough water in a bird's discharge to dissolve the urea, hence the white colour.
Urea also contains a large amount of fixed nitrogen. This is why guano, massive accumulations of petrified bird poo, used to be such a valuable agricultural fertiliser.
Hey, I got to say "poo" twice in a post, and nobody can tell me off for it.......he, he, he......one_rod.
