Ivory-bill Evidence from Sound and Video

At the American Ornithologists' Union (AOU) meeting in August, researchers from the Cornell Laboratory of Ornithology shared the latest results from the Ivory-billed Woodpecker search in Arkansas. In a series of four talks, Lab researchers explained search strategies, presented audio and video evidence, and emphasized the need for protecting the swamp forest ecosystem where the ivory-bill lives.

0n April 28, 2005, researchers from the Lab of Ornithology and collaborators published an article in Science Express reporting that the Ivory-billed Woodpecker had been rediscovered in the Big Woods of Arkansas. The article documented seven sightings of an Ivory-billed Woodpecker, presented frame-by-frame analysis of blurry video footage, and noted that promising sounds had been recorded.

Intriguing sounds

At the AOU meeting, the researchers played the audio recordings publicly for the first time. Simultaneously, the Lab of Ornithology released the sounds for public listening on the Internet at www.birds.cornell.edu/ivory. The recordings included notes resembling the Ivory-billed Woodpecker's nasal kent call, as well as double raps that researchers said could be the display drums of ivory-bills. One clip from January 24, 2005, captured the sound of a distant double knock, followed by a closer double knock 3.5 seconds later, possibly two ivory-bills communicating with one another.

The sounds were found among 17,000 hours of recordings from autonomous recording units developed by the Lab's Bioacoustics Research Program and attached to trees at 152 sites in the Big Woods. Special software programs helped flag thousands of sounds for scrutiny.

The researchers identified 54 double knocks that they believe could have been made by ivory-bills, said Russell Charif, a bioacoustics researcher from the Lab. They closely resemble recordings of display drums of six other woodpeckers in the same genus, Campephilus. Most of the double raps from the Big Woods were recorded near dawn or dusk, a pattern that would not be expected if they had been produced by random noises, such as gunshots or breaking tree branches.

Charif said, however, that the research team could not claim conclusively that the sounds were made by ivory-bills. No definitive audio recordings of the ivory-bill's display drum exists with which to compare the sounds from Arkansas.

James Tanner, who studied ivory-bills in Louisiana in the 1930s, described the ivory-bill's double knock as, BAM bam! with the first knock louder than the second. This differs from some of the Arkansas recordings, in which the second knock is slightly louder than the first. However, no one knows the extent to which these communication signals may vary depending on the individual bird, the region, or the context in which the sounds are made.

Researchers do have good audio recordings of ivory-bill kent calls with which to compare the nasal tooting calls from Arkansas. In 1935, Lab founder Arthur Allen, Peter Paul Kellogg, and colleagues recorded a pair of ivory-bills at a nest in the Singer Tract, Louisiana.

When heard at a distance through the forest, this known recording is strikingly similar to some of the calls from Arkansas. Computer analyses confirm that the kent-like calls match more closely with recordings of Ivory-billed Woodpeckers than with similar-sounding calls of White-breasted Nuthatches, another resident of the Big Woods.

The soundscape is muddled, however, by the presence of Blue Jays, notorious mimics. Blue Jays in the Big Woods sometimes utter notes that sound surprisingly similar to recordings of ivory-bills. How closely can a Blue Jay mimic an ivory-bill? Computerized comparisons using Blue Jay notes from the Lab of Ornithology's extensive sound collection show that the mystery calls from the Big Woods are more similar to known calls of ivory-bills than to those of Blue Jays. This field season, the search crew will be keeping their microphones on, not only for ivory-bills but for more calls of Blue Jays to use in the analysis.

Above, an Ivory-billed Woodpecker?s nest cavity, which was brought to the Lab of Ornithology by Arthur Allen in 1935 after the nest had been abandoned. By measuring the hole, researchers calculated the size of the ivory-bill in the 1935 film that had been perched next to the same hole (below). The bird filmed in 1935 and the bird filmed recently in Arkansas are both larger than Pileated Woodpeckers.

Photo by Tim Gallagher

Old film, new evidence

Additional evidence for the ivory-bill was captured in four seconds of video footage shot by University of Arkansas professor David Luneau on April 25, 2004. Ken Rosenberg, the Lab's Conservation Science director, presented an analysis, pointing out key marks and careful measurements to support the conclusion that the blurry image is an Ivory-billed Woodpecker.

In a dramatic moment at a plenary talk the following night, Lab director John Fitzpatrick revealed another piece of evidence. Frame-by-frame analysis shows that the bird in the video flew with 8.7 wingbeats per second, faster than Pileated Woodpeckers, which fly with 3-7.5 wingbeats per second.

Although no one had ever documented how fast an ivory-bill beats its wings, the 1935 sound-motion picture film had recorded an ivory-bill taking flight. Presenting a sonogram of the sound, Fitzpatrick showed that the ivory-bill in 1935 flew with 8.6 wingbeats per second, consistent with the bird on Luneau's videotape.

Saving the forests

Fitzpatrick's hour-and-a-half presentation also recounted the larger story of Ivory-billed Woodpeckers as part of a vanishing ecosystem--the old-growth forests of the South. He emphasized the need to protect the habitats as places for ivory-bills and for all wildlife.

Photo by Arthur Allen/CLO

"This is an American story about a bird that lived in the tops of the trees," Fitzpatrick said. "This is a bird that nested in the big old trees, foraged in the big old trees, and those trees were 80, 90, 100, and 200 years of age. Our job as Americans with respect to this bird and all of the other things that live beneath it is to bring back that old forest." He concluded his talk by saluting The Nature Conservancy and its Arkansas director, Scott Simon, for their past and continued work to save the Big Woods.

--Miyoko Chu

For complete video footage of the AOU presentations or to hear the sounds and view sonograms, visit www.birds.cornell.edu/ivory