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The Ivory-billed Woodpecker (Campephilus principalis) is an iconic species that has survived in barely detectable numbers for the past 100 years, during which it has been feared extinct only to be rediscovered several times. The most recent rediscovery was announced in an article that was featured on the cover of Science in 2005. The persistence of the Ivory-billed Woodpecker became controversial when ornithologists were unable to obtain a clear photo for documenting this ultra-elusive bird during multi-year searches at sites in Arkansas and Florida, where they had several sightings and were convinced these birds were present. Audio recordings of ‘kent’ calls and double knocks were obtained at both sites, but such recordings are not regarded as conclusive evidence of persistence. A debate on this issue that took place in Science and Nature focused on relatively weak video evidence obtained in Arkansas but excluded three videos obtained in Louisiana and Florida that show flights, field marks, and other behaviors and characteristics that are consistent with the Ivory-billed Woodpecker but no other species of the region. Kent calls were recorded in the 1930s, when other types of vocalizations were observed but not recorded, including a high-pitched alarm call. On two occasions in Louisiana, high-pitched calls were observed coming from the direction of an alarmed Ivory-billed Woodpecker, and several of them were recorded. The spectrograms of the high-pitched calls and all other known and putative vocalizations of the Ivory-billed Woodpecker consist of simultaneously excited harmonics. A harmonic oscillator model has been used to draw a connection between the drumming that is typical of most woodpeckers and the double knocks of the Ivory-billed Woodpecker and other Campephilus woodpeckers. Drumming corresponds to periodic forcing; double knocks correspond to impulsive forcing, and a single thrust of the body is sufficient to produce two impacts of the bill in rapid succession. The audio recordings from Arkansas and Florida were obtained with single microphones. A horizontal array of microphones would make it possible to detect weaker sounds and determine the directions of sources. This approach has the potential to lead to the discovery of a nest, and it might be more effective if the array is placed above the treetops, where sounds might propagate to longer ranges.

The Ivory-billed Woodpecker (Campephilus principalis) is an ultra-elusive bird that has repeatedly been feared extinct only to be rediscovered during the past hundred years. An article that was featured on the cover of Science in 2005 announced the most recent rediscovery in Arkansas, which was the first report of this species by ornithologists in several decades. Another group of ornithologists reported a series of sightings in Florida the following year, but the issue became controversial when nobody managed to get close enough to an Ivory-billed Woodpecker for a long enough period of time to obtain the clear photo that is regarded as the standard form of evidence for documenting birds. In Louisiana and Florida, video footage was obtained during three encounters with distant birds that were identified in the field as Ivory-billed Woodpeckers. The videos show field marks, body proportions, flights, and other behaviors and characteristics that are consistent with the Ivory-billed Woodpecker but no other species of the region. The five most compelling events in the videos are the focus here, but several additional events are also discussed. During four of the most compelling events, the audio track contains sounds that are consistent with the Ivory-billed Woodpecker. Extensions of previous results include a size comparison and a wingspan estimate that are used to fortify the analysis of two videos from Louisiana. Takeoffs with deep and rapid wingbeats and loud ‘wooden’ wing sounds, which were overlooked during previous analysis of a video that was obtained in Florida, are consistent with an account by Tanner. Additional events in the Florida video are also discussed, including a sudden maneuver during a swooping flight that coincides with ‘spring-like’ sounds. This issue started to evolve into a science scandal when critics, who had become entrenched in the position that the Ivory-billed Woodpecker is extinct, used specious arguments to cause a long delay in the publication of evidence that should be sufficient to establish persistence. After openly targeting relatively weak evidence, critics avoided engaging in open discourse on the strongest evidence after it was finally published. Some of the leading science journals helped to enable the scandal by failing to provide diligent oversight and publishing biased reports on the status of this issue. The scandal culminated in a decision by the U.S. Fish & Wildlife Service to declare the Ivory-billed Woodpecker extinct, which was made in the absence of an open discourse on the strongest evidence and in the wake of an unprecedented spike in published reports of sightings during the searches in Arkansas, Florida, and Louisiana.