Ivory-billed Woodpecker Fact Sheet

Ivory-bill Search Technology

April 28, 2005—With thousands of acres to cover in the White River and Cache River National Wildlife Refuges in Arkansas, searchers knew they couldn’t be everywhere at once. Instead, they relied on remote sound-recording technology in hopes of capturing the “kent” call of the ivory-billed woodpecker and its double-knock “BAM-bam.” They also relied on remotely operated cameras to capture photographic proof that the elusive bird exists.

Remote sound-recording: The sound recording-and-analysis process begins in the field with devices called autonomous recording units (ARUs). About the size of a palm-held computer, the ARU includes a small hard drive and the circuitry to start and stop recording – typically about four hours when ivory-bills wake up in the morning and four hours before they retire in the evening – plus a processor for digital signals. The gear is concealed in a two-foot-long piece of PVC plumbing pipe.

Outside the pipe, a furry “wind sock” covers the 16-microphone array to filter ambient noise, although non-bird sounds – such as distant train whistles and gunshots – can become part of the recording.
The ARUs are strapped to trees in the wetland area, safely above water level, although periodic flooding can change water levels 10 feet or more in a month.
Two 6-volt lantern batteries power the unit for each week-long recording session. Technicians canoe through the swamp areas to retrieve the ARUs and download the recording to a larger hard drive, which is shipped back to Cornell University’s Lab of Ornithology in Ithaca, N.Y., for analysis. Equipped with fresh batteries, the ARU is then moved to another location.
To survey the 160,000-acre search site, ARUs are moved frequently and spaced as far apart as possible. The bird’s “kent” call can be recorded up to 200 meters (656 feet) away, while the double-rap sound carries about 300 meters (984 feet). If one unit detects a promising sound, others can be moved nearby to “triangulate” the source.
The ARU was invented at the Lab of Ornithology’s Bioacoustics Research Program and has been used to record everything from right whales in the North Atlantic to Africa’s forest elephants. A total of 24 ARUs were used in the Arkansas search for the ivory-bill.

Sound analysis: Recordings from the Arkansas survey (eight hours a day from each of 24 units) are the equivalent of nearly three years of continuous recording. Before human ears take over, the first part of the detection process is automated.

Two Cornell-developed sound visualization and measurement programs, called XBAT and Raven, are used. XBAT (for eXtensible BioAcoustic Tool) rapidly scans the digital recordings and detects sounds similar to those made by ivory-bills. Raven is used for interactive exploration of 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 plays and replays each detected event, sometimes comparing the sound to reference recordings of ivory-bills, their close relatives, or other species that sound almost alike. As the search neared the midpoint, analysts had already scrutinized 91,000 “detections,” and set aside all but a handful.

Remote imaging: Originally marketed as “wildlife cameras” to deer hunters who have feeders or other places where deer might frequent, four Cam Trakker and four TrailMac cameras were used in the search for the ivory-billed woodpecker.

The cameras use an integrated infrared, heat-and-motion sensor with sensitivity settings that, when activated, cause the digital camera to take a picture. The frequency at which pictures can be taken is adjustable, as is the quality of the digital picture (or video). Both manufacturers use off-the-shelf digital cameras and modify them to take pictures when the sensor is activated.
“The cameras were tested for use with birds by focusing them on backyard feeders,” says David Luneau, a professor of electronics and computers at the University of Arkansas at Little Rock. “At their most sensitive settings, neither model did well photographing small birds such as Carolina chickadees and tufted titmice beyond two meters. But the cameras performed well at closer range on these smaller birds. Since the ivory-billed woodpecker is a much larger bird, we calculated the cameras should be placed no more than 5 meters from the target.”
Search team members positioned remote cameras to target trees showing evidence of bark “scaling.” Ivory-bills strip bark from recently dead trees to search for beetle larvae that live just under the bark.
“If an ivory-bill can be caught on camera, we will learn more about the number and sex of the birds in the area,” Luneau says. “If other birds are photographed on scaled trees, we will learn more about the types of birds that feed on larvae and insects from these trees. Most importantly, if we can learn enough about different types of scaling to determine precisely the appearance of ivory-bill feeding signs, we can better identify areas where ivory-bills are present and concentrate our search efforts in these areas.”

For More Information About the Ivory-billed Woodpecker:

Found: The Ivory-billed Woodpecker
Learn about the timeline of the search for the ivory-bill, The Nature Conservancy's conservation efforts in the Big Woods of Arkansas, meet the search team, and more!
Live audio chat about the ivory-billed woodpecker with Phillip Hoose
Phillip Hoose, author of The Race to Save the Lord God Bird, discusses the recent rediscovery of the ivory-billed woodpecker.
Where We Work: The Nature Conservancy in Arkansas
The Nature Conservancy's work in Arkansas helps protect and restore ecologically rich wetlands, threatened native prairies, caves, forests and waterways.
Places We Protect: The Big Woods of Arkansas
This 550,000-acre corridor of floodplain forest follows the bayous and rivers that flow into the Mississippi River and includes the most extensive example of natural shoreline along the lower Mississippi. For 41 miles, the banks on both sides of the river are lined with bottomland hardwoods, the habitat of the ivory-billed woodpecker.
How You Can Help: Donate Online
Support our efforts to conserve this critical habitat for the ivory-bill and other species.
Ivory-billed Woodpecker News
See ivory-billed woodpecker photos, maps of the habitat of the ivory-bill, and other news and information about the rediscovery of the ivory-billed woodpecker.