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Similarities between Campephilus woodpecker double raps and mechanical sounds produced by duck flocks.

Article Excerpt
Evidence for survival of Ivory-billed Woodpeckers (Campephilus principalis) in Arkansas and Florida includes recordings of "double raps" (DRs) from autonomous recording units (ARUs) in White River National Wildlife Refuge (WRNWR) and along the Choctawhatchee River, which sound much like the double raps of some Campephilus woodpeckers (Charif et al. 2005, Hill et al. 2006). Although no unequivocal recording of the double rap of an Ivory-billed Woodpecker (IBWO) exists, written descriptions indicate it was similar to those of other members of the same genus (Tanner 1942). We believe many ARU DRs from Arkansas and Florida were likely produced by aerial duck flocks when flock members flying in close proximity hit wingtips. We observed three sets of DRs produced by flying Gadwall (Anas strepera) flocks at WRNWR on 21 December 2005. Prior to this observation, we were unaware of the "duck wingtip collision" (DWC) phenomenon, and we subsequently discussed our finding with members of the 2005-06 Cornell Laboratory of Ornithology search crew. We then observed and recorded an identical event from a Gadwall flock at Eagle Lake, Texas on 2 January 2006. In both cases, these sounds were associated visually with duck flocks. No visual sightings were associated with ARU recordings. CDJ worked as a member of the IBWO search team from December 2004 to April 2005. During this time, to his knowledge, field crews were not informed of the DWC phenomenon. Here we compare DWCs from our recording with ARU DRs from 24 January and 5 February 2005 (http://www. birds.cornell.edu/ivory/multimedia/sounds).

METHODS

We recorded a series of DWCs from a Gadwall flock using a Sony TCM5000EV cassette recorder with a Sennheiser MKH416T shotgun microphone at Eagle Lake, Texas (96[degrees] 19' 43" W, 29[degrees] 35' 15" N) on 2 January 2006. We measured...