What is the main excretory product of birds and lizards?

The primary excretory product of birds and lizards is nitrogenous waste in the form of uric acid. Unlike mammals that primarily produce urea as their primary nitrogenous waste product, birds and lizards have evolved to conserve water through their renal system. Uric acid is less toxic than urea and requires minimal water for its excretion, allowing these animals to survive in environments where water may be scarce. This adaptation plays a significant role in their ability to thrive in various habitats, including arid and semi-arid environments.