 During the day, it's bird time, and you can see the birds all around. But then there's a point in sunset where it stops being bird time, and it starts being bat time, and that's when the bats all come out. And that's almost now. And that's almost now. Finally, we approach a dock, and a tall woman greets us as we climb out of the boat. I've got to hug these people. This is Nancy Simmons. She's a curator of mammology at the American Museum of Natural History in New York.