All animals excrete Urea. In mammals, in comes out in the form of a liquid(urine). In reptiles, amphibians and birds it's excreted in a pasty white material known as urates. That is why bird dropping and reptile droppings have both a dark brown to black(feces) section to them and also a white, chalky looking section(urea). So, in a sense, they do "pee" just not in the same form as mammals.