I had thought that maybe it was so you would be able to see it on the blacktop:
The above two photos are of my walk between the garage and the house. We have some lovely morning doves that love to hang around there and everytime you go out or come in they take off leaving behind them a stream of "White Bird Poop."
Now here is the question. Why is Bird Poop White? Now this may be a little more than you need to know, but here it is and you will no longer need to ponder the question:
Many people wonder why bird poop is white. The reason bird poop is the white color it is instead of brown like most other animals has to do with the fact that birds, unlike mammals do not urinate. Their kidneys excrete nitrogenous wastes in the form of uric acid. Uric acid has a low solubility with water, so it comes out as a white paste.
This excrement, as well as the output of the intestines, emerges from what is called the cloaca. The cloaca is a multi-purpose hole for birds: their wastes come out of it, they have sex by putting their cloacas together, and females lay eggs out of it.
Now if there is anything else you might like to know regarding this, you can click on the following link, however, when you leave the forum this morning you will have just one more piece of valuable information.
http://www.bellaonline.com/articles/art21226.aspNews is slow today.