Chirpy Boy is a Bolivian Tree Lizard that Bart named. His brother is Bart Junior.
After shooting a bird with Nelson Muntz's BB gun, Bart cares for the eggs found in the bird's nest. When the eggs hatch, the family is surprised to find that they were actually lizard eggs. Bart, continuing with his motherly impulses, names the hatched lizards Chirpy Boy and Bart Junior. When Bart brings them to the local Bird Watching Association to ask what type of bird they are, Principal Skinner tells him that they are dangerous lizards that eat pigeons and must be killed. After a brief chase to the roof of the building, Principal Skinner tosses the lizards from the roof. Bart assumed the lizards died but in actuality, they deployed their "wings", glided to the ground safely and ended Springfield's pigeon infestation.