bird excretion

[long john]

do birds urinate? or does it all come from there ass?

[Ouisch]

http://www.straightdope.com/mailbag/mbirdpee.html

 

The above link has a detailed explanation, but the basic answer is that the bird droppings you find on your windshield (sorry, windscreen) are a combination of urine and feces.  Birds don't have a bladder, so liquid waste passes through the same tract as disgestive waste.