Zoology is an optional subject for the UPSC civil services exam that is suitable for candidates with a background in zoology, medicine, botany, life sciences, agriculture or forestry. The document provides tips for preparing for the zoology optional paper, which includes knowing the syllabus, selecting reference books, creating a study plan, and focusing on important topics from previous years' exams. Key steps are to understand the syllabus, choose recommended books, devise a preparation schedule, and focus on high-yield topics.