These form when bacteria like Proteus mirabilis, Proteus vulgaris, and Morganella morganii use the enzyme, urease, to split urea into ammonia and carbon dioxide.

当细菌如变形杆菌、普通变形杆菌、摩根氏菌存在时就会形成鸟粪石，细菌利用尿素酶将尿素分解成氨和二氧化碳。