June 18, 2013
After getting so much out of his birdwatching tour in Bryant Park, I wanted to hang out again with Gabriel Willow, this time on the so-called Bat Walk, an exploration of Central Park at night.
Willow, the Wizard of Audubon, has an uncanny command of these tours, as though he and Nature worked out the script beforehand. Near Strawberry Fields a bluejay is making a racket. “That’s a danger call,” Willow says, “so there’s probably a predator somewhere near.” The phrase is barely out of his mouth before we spot a hawk hunching on the next branch over. Willow points out a gray catbird in a bush. “It got the name because the early settlers thought it sounded like a cat”—the catbird meows—“but it can also mimic other birds”—the catbird tootles. In the Ramble he says, “Right about this time is when the raccoons wake up. Gotta come down and go to work, start raiding trashcans.” And promptly a bushy adult clambers grudgingly from its bed high up in a sweetgum tree.
The Bat Walk, offered through Sidetour, starts at twilight, when the day shift fauna settles down and the night shift comes on. Once you’ve been sensitized, you’ll believe you can feel this changeover taking place quietly around you. The air is actually different: Willow notes that at twilight fragrances are more pronounced as the humidity rises, and the trees open the pores in their leaves, releasing the day’s store of oxygen. When one of the tour-goers thinks she sees some motion in a tree, Willow holds a flashlight at his temple and homes in on the spot. “Ah,” he says. “Baby raccoons.” Holding the beam next to your head puts you at an angle to catch the reflection splashing from the backs of a nocturnal animal’s eyes; one by one we try it ourselves: nothing in the black tree, and then—pairs of gleaming, living dots, shyly observing.
When the first bats come out, the sky is still light enough that you can see them darting above the trees.
Thanks to electronics, you can also hear them. “I have this nifty device here called a bat echolocator,” Willow says, pulling from his backpack a small black box. It brings down the bat’s impossibly high-pitched bursts to within the range of human hearing. Willow turns the dial to above 30 kHz, into the frequency range of red bats, which are the most common of the half-dozen species found in Central Park. Soon the machine fires off a series of eerie chitters.
There’s something beautifully strange about this perceptual eavesdropping. The navigating signal a bat makes is generally entirely private. It isn’t a call: it has no message to convey. You could think of it as a sonic paint that the bat sprays over the world in order to “see.” With echolocation bats can resolve an object as fine as a human hair; in Central Park, they use it to hunt flying insects, emitting a base signal that will speed up for greater resolution as they approach prey.
It feels like sorcery, but Willow is quick to offer context. “We tend to categorize,” he says, “but the senses are basically just perceiving waves of things: your eyes are perceiving light waves and your ears are perceiving sound waves. But we’ll never now what it’s like. We can figure out the mechanism but not the reality.”
Pondering the reality of bats, in the cool aromatic depths of Central Park, is a good way to spend an evening. Listen to the echolocation for yourself: