http://www.straightdope.com/mailbag/mbirdpee.html
Thanks, Colibri, for this article.
Quote: “A bird dropping usually contains both white uric acid crystals, and a concentrated mass of digestive wastes such as insect cuticle or seeds.”
That “concentrated mass”, though Colibri didn’t spell this out, would be the darker stuff found in bird droppings – the avian equivalent of fecal matter, or so I’ve read. I’ve never researched this personally, though once in high-school science class my lab partner and I did examine rabbit pellets under a microscope. (This was a serious scientific experiment and actually fascinating – the rabbit had been eating something that looked like grass.)
Hey! How about lunch! 