The Double Knock on Wood

BAM-bam recordings suggest the presence of ivory-bills
Ivory-billed Woodpeckers rap twice on wood as long-distance communication signals, with the first strike usually louder than the second: “BAM bam!” In Central and South America, woodpeckers in the same genus (Campephilus) also communicate with double raps, but the ivory-bill is the only species in the United States with this distinctive double-knock display drum.

To help find double knocks among thousands of hours of recordings, researchers rely on advanced sound-processing software developed by the Cornell Lab of Ornithology’s Bioacoustics Research Program. The software has isolated thousands of recordings that resemble double knocks. Analysts carefully examine each one to rule out whether they could have resulted from other sounds, such as breaking tree branches, raindrops, mechanical noises, other woodpeckers, and gunshots (the study site is in a duck-hunting area).

Listen to recordings of double-knock sounds, then read results of the analysis.

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