system
Given the following post, respond as if you're commenting on Reddit:
human
Why is bird poo white?

What is it that makes it white?
gpt
Birds and reptiles have a different way of getting rid of ammonia (NH3) than mammals.  Mammals convert the ammonia to urea (CO(NH3)2), dilute it with water and excrete it as urine.  Birds, however, convert the ammonia to uric acid (C5H4N3O3) and excrete it along with feces.  Uric acid is white.  Hence bird poop is white.