Robin explained to me that Big Bird had moved to New York to be with the Ninja Turtles. And it is, to the best of my recollection, true that in the Muppet Movie, the very first one, Big Bird moves to New York instead of going to Hollywood with Kermit and Fozzie. And in Robin's mind, people in New York know each other. Because they live near each other, there in New York.
I really love the fact that, in his little brain, Big Bird and his beloved Turtles are having pizza together. And maybe in a few years Edna St. Vincent Millay will join them. This just makes me happy.