Complex sentence: The pond developed in the preserve, which in the 1920s was a garbage dump, at the initiative of the Audubon Society, has become a sanctuary for resident and migratory birds and many species of wildlife.
Split into simpler sentences: The pond developed in the preserve, which in the 1920s was a garbage dump, at the initiative of the Audubon Society. It has become a sanctuary for resident and migratory birds and many species of wildlife.