urate
Birds, reptiles, insects and some mammals (such as the kangaroo rat) excrete excess nitrogen in the form of uric acid, rather than the urea found in the urine of humans and most other mammalian species. In snakes, lizards and crocodilians, this substance is a hard white chalk-like substance, while it appears as a viscous white fluid (often mistakenly referred to as feces) in birds.