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Chirpy Boy is a Bolivian Tree Lizard that Bart named. His brother is Bart Junior.

After accidentally shooting a bird with Nelson Muntz' 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 bird eggs, and leave their own in their nests which hatch and eats the unsuspecting mother bird. Skinner says that they 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 would die, but they actually deployed their "wings", glided to the ground safely and ended Springfield's pigeon infestation.