Mary Oliver is a nature poet. In Wild Geese she compares natures condition to the human condition using Wild Geese as an example. If you read the poem wild geese are mentioned numerous times. Often, poets do not put as much thought into naming their works as other writers do. (Don't get mad at me if you are a poet and do not believe that it is the case)
He resembles the world with wild goose; inviting you to think no more of that wild creature. Wild geese are the social restrictions.