Login

Join for Free!
119213 members
table of contents table of contents

The apparent rediscovery of the Ivory-billed Woodpecker Campephilus principalis in Arkansas, USA, …


Biology Articles » Zoology » Ornithology » Video analysis of the escape flight of Pileated Woodpecker Dryocopus pileatus: does the Ivory-billed Woodpecker Campephilus principalis persist in continental North America? » Background

Background
- Video analysis of the escape flight of Pileated Woodpecker Dryocopus pileatus: does the Ivory-billed Woodpecker Campephilus principalis persist in continental North America?

The reported rediscovery of the Ivory-billed Woodpecker in 2004–5 in the Big Woods of Arkansas gave new impetus to efforts to conserve the mature bottomland woodlands of the south-eastern USA. Several sightings have been reported without photographic evidence being obtained [1]. Unless sightings are, however, independently verifiable on the basis of photographic or other recorded evidence, the possibility that mistakes have been made cannot be eliminated. Crucial to the scientific case for the persistence of the Ivory-billed Woodpecker was a 4 s video of a large woodpecker in flight recorded by M.D. Luneau on 25 April 2004 (henceforth referred to as the 'Luneau video') and published in 2005 [1], which was claimed to be inconsistent with the plumage patterns of the superficially similar Pileated Woodpecker (a common resident bird of the area). Both species are large, black-and-white woodpeckers [2]. The upperwing of the Ivory-billed Woodpecker is black, with white secondary feathers and white on some inner primary feathers. Pileated Woodpeckers have a largely black upperwing, with white restricted to the 'wrist' due to white bases to the primary feathers. The underwing of Pileated Woodpecker has all-white underwing coverts, giving an appearance of a white underwing with a broad black outline (the black flight feathers). These plumage differences result in the Ivory-billed Woodpecker having a white trailing edge to the wings (upper and lower sides), whereas the Pileated Woodpecker has a black trailing edge to the wings. Both species have black wing-tips. These and other plumage characteristics are shown in [1,2]. The wingbeat frequency of the bird in the Luneau video was measured at 8.6 beats s-1, similar to that inferred from archival sound recording of a single Ivory-billed Woodpecker, but claimed to be outside the range of Pileated Woodpeckers (which generally have slower wingbeats) [1,3].

Sibley et al [4] questioned the video evidence, in particular providing alternative explanations for the plumage patterns of the Luneau bird in flight and at rest. They pointed out individual frames of the Luneau video that appear to show three features that are each inconsistent with Ivory-billed Woodpecker: (1) apparently black secondary feathers on the upper surface of the left wing, (2) particularly bright white primary bases, and (3) a black band curving smoothly round the wing tip (see Figure 3 in [4]). They hypothesized that flexing of a Pileated Woodpecker's wings during flight could produce the appearance of white trailing edges on both wings in low-quality videos [4]. They offered, however, no direct evidence to show that this could cause a video of a Pileated Woodpecker to look like the bird in the Luneau video. Fitzpatrick et al [5] in turn rebutted some aspects of the hypothesis of Sibley et al [4], publishing video stills of Pileated Woodpeckers, and a model of a Pileated Woodpecker, that appeared to show a black trailing edge to the wings inconsistent with Ivory-billed Woodpecker and the Luneau video. Fitzpatrick et al [5] neither rebutted nor discussed the three key inconsistencies described above. Without further evidence, this became largely a theoretical debate over interpretation of field characters that were barely visible in the very small images originally obtained. On one hand, as pointed out in Sibley et al [4], some of the frames of the bird in the Luneau video do appear to be inconsistent with Ivory-billed Woodpecker. On the other hand, the flight pattern of the bird in the Luneau video is asserted to be atypical for Pileated Woodpecker (but matching anecdotal descriptions of Ivory-billed Woodpecker). Furthermore, the general impression of the bird in the Luneau video was that there is far too much white in the wings for it to be a Pileated Woodpecker, and that if it was a Pileated, then it must be an aberrant one with abnormally extensive white plumage. Such birds occasionally occur, and have been observed in the Arkansas study area [6].

This study was undertaken to determine whether the flight and plumage of the bird in the Luneau video really was inconsistent with either a normal or partial albino Pileated Woodpecker. Independent analyses of the plumage patterns and wingbeat frequencies observable in Pileated Woodpeckers are presented, and it is concluded that the identification of the bird in the Luneau video as definite Ivory-billed Woodpecker is probably unsafe.


rating: 4.50 from 2 votes | updated on: 23 Oct 2007 | views: 5251 |

Rate article:







excellent!bad…