Quoting from their website:
The Association was named for Frank Lebby Stanton's poem, The Graveyard Rabbit. Although the poem is about superstitions associated with graveyard rabbits, Stanton also establishes that such rabbits have a charmingly intimate knowledge of graveyards and a loving association with the dead. These traits are the motivation of the human beings interested in this group.There are people associated with the Graveyard Rabbits in many states and some countries, other than the United States. Collectively, they are a huge knowledge base about local cemeteries and burials.