The Bolivian Tree Lizard is a parasitic ovoraptor that lays its eggs in other birds nests, then eats the original eggs. The mother bird will continue to nurse the eggs thinking they are hers. After the eggs hatch, the young Lizards eat the mother bird too. where Bart hatched a pair (whom he originally thought were the babies of a mother bird he accidentally shot) which he named Chirpy Boy and Bart Junior. When he brought them to the attention of the community a group of people (including his principal, Principal Skinner) decided that the lizards needed to be killed to protect the native wildlife. However, with the help of his mother Bart manages to flee with the lizards onto the roof; where both of them escape by gliding to the ground and running away. Bolivian Tree Lizards once took care of Springfield's bird problem, they then became extinct in Springfield because snakes were introduced into the wildlife.
Behind the Laughter
There is no such thing as the Bolivian Tree Lizard. This fictional species is a mix-match of real reptiles, combining the looks of a tree iguana, gliding membranes like those of South-East Asian dracos, the egg and bird-eating habits of snakes and how the dinosaur Oviraptor philoceratops was thought to have stolen other dinosaur eggs. The conduct of replacing birds' eggs with their own is probably inspired by the Cuckoo, one of the birds that Skinner - erroneusly - claims to have exterminated.