Using Bioacoustics Technology to Search for a Secretive Woodpecker

Photo by Melanie Driscoll/CLO

Searching for Ivory-billed Woodpeckers involves countless hours of slogging through swamps or sitting hidden in one place, endlessly waiting for one of the rarest birds in the world to show up. But that's only part of the story of the research going on in Arkansas. In addition to human searchers, the Lab of Ornithology strapped 24 autonomous recording units (ARUs) on trees in the Cache River and White River refuges during this study season.

The units can record the distinctive kent calls of an ivory-bill from up to 200 meters away and their double-rap display drum from even farther. Designed and built at the Lab, the ARUs consist of a small hard-drive and the circuitry to start and stop recording (each unit records for four hours in the morning and four hours in the late afternoon, when the birds are most active) plus a processor for digital signals, encased in a two-foot-long piece of PVC plumbing pipe. Outside the pipe, a furry windsock covers a 16-microphone array. Each unit is deployed for two to four weeks, then retrieved by field technicians who download the data, replace the batteries, and move it to a new location. The data from the ARU are shipped back to Cornell for analysis. There the fun begins.

A team at the Lab of Ornithology led by Russ Charif must go through the recorded sounds, searching for likely calls or raps. The ARUs recorded about 900 hours of sound per week—that's a whopping 18,000 hours to date. Fortunately, the first part of the process is automated. Two Lab-developed sound visualization and measurement programs, called XBAT and Raven, are used. XBAT rapidly scans the digital recordings, detecting sounds similar to those made by ivory-bills. Raven is used to examine sounds that are of particular interest. On the sound spectrograms, XBAT highlights sounds of interest with colored boxes to catch the eye of the analyst.

The analyst replays each "detection" repeatedly, sometimes comparing the sound with known recordings of ivory-bills, their relatives, or similar-sounding species. More than 100,000 detections have already been scrutinized. Most have been ruled out, but a few are tantalizingly similar to known ivory-bill calls or to the double-raps of Latin American Campephilus woodpeckers. These will be studied in the months ahead.

For permission to reprint all or part of this article, please contact Jennifer Smith, Cornell Lab of Ornithology, 159 Sapsucker Woods Rd., Ithaca, NY, 14850. Phone: (607) 254-2497. email: jls39@cornell.edu