This series of Blastoff! Readers, level 1, provides young readers with nonfiction books in a simple format.  Warthogs are wild pigs.   The bumps, or warts, on the sides of their heads provide protection during skirmishes with each other or predators.  Each spread contains two sentences in large font and a large, colorful, well-chosen photograph.  Nonfiction books to read for further information are mostly written at a similar level.  One, a fiction story, is written at a higher level.  The Factsurfer internet site has some good pictures and videos of warthogs, but the reading level is higher than first or second grade.  Good basic introduction to nonfiction for young readers.