Science News
from research organizations

Cornell Researchers Say Double Knocks May Be 'Soundprints' Of Ivory-bills

August 26, 2005
Cornell University
After analyzing more than 18,000 hours of recordings from the swampy forests of eastern Arkansas, researchers at the Cornell Laboratory of Ornithology have released recordings offering further evidence for the existence of the ivory-billed woodpecker.

ITHACA, N.Y. -- Now hear this: After analyzing more than18,000 hours of recordings from the swampy forests of eastern Arkansas,researchers at the Cornell Laboratory of Ornithology at CornellUniversity have released recordings offering further evidence --including the legendary bird's distinctive double knock -- for theexistence of the ivory-billed woodpecker, once thought extinct. Thesesounds were recorded in the same area of Arkansas where the species wasrediscovered in 2004.

The Cornell researchers announced theresults at the annual meeting of the American Ornithologists' Union inSanta Barbara, Calif., Aug. 24, and they have invited the public tolisten to the calls and knocks on the Web at

The recordings reveal sounds that,experts say, are strikingly similar to those made by ivory-billedwoodpeckers and provide compelling information that can be added toevidence already gathered of the bird's existence. One of therecordings, from Jan. 24, 2005, captured a distant double knock, "Bambam!" followed by a similar and much closer double knock 3.5 secondslater -- possibly the drumming displays of two ivory-billed woodpeckerscommunicating with one another by rapping on trees.

"Iimmediately felt a thrill of excitement the first time I heard thatrecording," said Russell Charif, a bioacoustics researcher at theCornell Lab of Ornithology. "It is the best tangible evidence so farthat there could be more than one ivory-bill in the area."

Only asingle bird at a time was documented through sightings and videofootage during a yearlong search of the area in 2004-05. Whether morethan one bird exists is still a big question, Charif said, butquantitative analyses of the most promising sounds indicate a highprobability that they were made by ivory-billed woodpeckers.

Thesounds were recorded on autonomous recording units (ARUs) designed bythe Cornell lab and strapped to trees in the swamp. More than 150 siteswere monitored in the half-million-acre "Big Woods" of Arkansas.

Aftereliminating thousands of noises from gunshots and other sources, theresearchers found about 100 double knocks that bear a strongresemblance to the display drumming of the ivory-bill's closestrelatives. The sounds were clustered around certain recording locationsat certain times of day -- a pattern that would not be expected if theyhad been produced by random noises.

Then ARUs also recorded nasaltooting calls similar to those of ivory-billed woodpeckers. Charif saidblue jays are notorious vocal mimics that sometimes utter calls likethose of ivory-bills. However, he added, a sophisticated acousticclassification program categorized nearly all of the unknown calls fromArkansas as most similar to ivory-billed woodpecker recordings. Nonematched up with "tooting" calls of blue jays from the Cornell lab'saudio collection, but the researchers say they cannot rule out bluejays until they analyze more variants of the calls.

"We'reexcited and encouraged by the acoustic analysis," said JohnFitzpatrick, director of the Cornell Lab of Ornithology. "These soundsgive us additional hope that a few ivory-billed woodpeckers do live inthe White River and Cache River region. But this species is still onthe verge of extinction and huge mysteries remain to be solved.Certainly, we have a lot more work to do before we know enough todetermine its population size, let alone ensure its survival."

Ateam led by the Cornell Lab of Ornithology, The Nature Conservancy, theU.S. Fish and Wildlife Service, the Arkansas Game and Fish Commission,and other partners, will renew search efforts in the Big Woodsbeginning Nov. 1.

Story Source:

Materials provided by Cornell University. Note: Content may be edited for style and length.

Cite This Page:

Cornell University. "Cornell Researchers Say Double Knocks May Be 'Soundprints' Of Ivory-bills." ScienceDaily. ScienceDaily, 26 August 2005. <>.
Cornell University. (2005, August 26). Cornell Researchers Say Double Knocks May Be 'Soundprints' Of Ivory-bills. ScienceDaily. Retrieved May 23, 2017 from
Cornell University. "Cornell Researchers Say Double Knocks May Be 'Soundprints' Of Ivory-bills." ScienceDaily. (accessed May 23, 2017).