On Tuesday, ornithologists who had expressed doubts about the rediscovery of the ivory-billed woodpecker said they are now convinced that the bird is alive and well. New sound recordings of the woodpecker—which hadn't been seen since 1944—brought the skeptics around. "Once everybody hears these vocalizations, you can't help but be convinced," said one expert. How do ornithologists know what an extinct bird sounds like?
They use written descriptions of the bird's call, examples from similar species, and—if they're lucky—sound recordings. Some of the first successful recordings of birds were made on motion-picture sound film beginning in 1929, when Arthur Allen, the founder of the Cornell Lab of Ornithology, pointed a microphone at birds in a local park. By the mid-1930s, Allen and his associates were using the technology to make audio and visual records of birds in the field, and in 1935, they managed to record the ivory-billed woodpecker. (Click here to listen and here to see.) Until a few months ago, Allen's audio clip was the only known recording of the bird's call.
Allen's clip includes the woodpecker's kent call—which sounds like someone saying the word "kent" in a nasal voice—but not its distinctive "double-rap." (The ivory-billed woodpecker, unlike some other varieties, bangs its beak on a tree twice in rapid succession: Bap-bap!) But the new recordings of the bird that convinced the skeptics featured the double-rap that was missing from Allen's sound film. So how did they recognize the sound?
First, the double-rap recalled the sounds made by nine other birds of the same genus (Campephilus) that live in Central and South America. Second, the recording featured two double-raps—one close to the microphone and one farther away—made in rapid succession, as if two birds were communicating with one another. Although it's possible that gunshots or an errant call from another species of woodpecker could sound like a double-rap, it's far less likely that random noises near a microphone would produce two double-raps in a row.
Ornithologists also relied on written accounts of the double-rap from the 1930s and '40s. Before Allen began his recording work, most information about bird sounds was passed along in onomatopoeias, like the woodpecker's kent call. The white-throated sparrow, for example, has long been known to say old man Peabody, Peabody, Peabody, while the yellow warbler goes sweet-sweet-sweeter-than-sweet. What was once known as the Traill's flycatcher turned out to be two distinct species that happen to look very much alike—the alder flycatcher and the willow flycatcher. One chirps ree-beo, and the other fitz-bew. (Some birds, like the cuckoo, are named after the sounds they make.) Mnemonics like these are still used in field guides and help modern bird-watchers identify animals in the wild.
In the early 20th century, some ornithologists even attempted to translate bird calls into musical notation. The bird-watcher and composer Olivier Messiaen had perfect pitch; he was known for ambling through the French countryside and recording the calls he heard on staff paper.
Explainer thanks Jack Bradbury of Cornell University and Richard Prum of Yale University.