Reviewer #1:

Everyone who is even remotely familiar with the events and evidence over the last several years regarding the possible persistence of Ivory-billed Woodpeckers sincerely hopes that the breakthrough evidence will finally appear. That evidence must contain absolutely unequivocal, sharply defined photographic or video images that can be clearly and unambiguously assigned to this iconic species. Such a report would clearly merit publication in PNAS. But until such clear-cut evidence is available, even those of us who find the original Arkansas evidence to be convincing are wary of any report of Ivory-billed Woodpeckers that offers only blurry, indistinct photographs, brief fuzzy videos, and sounds of uncertain identity. Such reports simply add fuel to the fire of skeptics who argue that this whole effort is nothing more than a search for another 'Bigfoot.'

Unfortunately, this report by Collins falls into the latter category. Simply put, neither the manuscript nor any of its copious supporting materials offers even a single unambiguous image of an Ivory-billed Woodpecker. All images and videos are blurry, distant, and indistinct. Worse, in no case can the vastly more likely Pileated Woodpecker be ruled out, and several actually appear to me to represent this common species. Therefore, the claim that the high-pitched sounds presented here are those of an Ivory-bill is unsubstantiated, as is the claim that the flight characteristics shown in the focal video represent those of an Ivory-bill.

I urge Collins to submit his sound recordings to an independent acoustic analysis by trained bioacoustic experts. His written description seems naïve (e.g., his reference in Fig. 1 to frequencies that "appear to be excited simultaneously" suggests that he is not familiar with the term "harmonics" and its profound importance in comparing the vocal signatures of birds). Nothing about these sounds seems extraordinary to me, and certainly nothing about them rules out Blue Jay, several species of blackbird, or even White-breasted Nuthatch as potential sources.

The images in Fig. 2 are simply too indistinct to identify the bird to species. The images in Figs. 3, 4, and 5 are actually consistent with Pileated Woodpecker, as they show a slender, whitish neck and relatively shorter, narrower bill compared to the enormously oversized bill of Ivory-billed Woodpecker. Fig. 6 demonstrates little, as Pileated Woodpeckers are indeed known to flap very rapidly (up to 8 beats per sec) during the first several wingbeats after take-off.

It is certainly possible that Collins has located Ivory-billed Woodpeckers, and that he has seen them clearly himself. If so, then this reviewer encourages him to keep at the effort until he can obtain photographs or videos that the entire ornithological world will agree about. As stated above, such a report would certainly merit publication in PNAS.



Reviewer #2:

This paper describes 7 encounters over a five day period the author claims to have had with Ivory-billed Woodpeckers (IBWs) on the Pearl River in Louisiana, and one similar encounter in Florida. What is novel about the content, besides of course a report of the species from a third area (Arkansas and Florida being the previously reported areas), is information about a third type of vocalization (other than kent calls and double knocks) that may indicate the presence of the species.

Following all the criticism of the report of IBWs from Arkansas, high standards have been set for what constitutes acceptable evidence of the presence of IBWs. The evidence presented here does not come close to meeting these standards in my opinion. None of the video is conclusive, and only a cursory analysis of the putative IBW calls is provided. Most importantly, there apparently has been no independent, outside review of any of these observations. In conjunction with the regional search effort, USFWS has established a process for vetting possible sightings and recordings of IBWs through an evidence review process. There is no indication that these observations have been submitted for this examination. There is thus no corroberation of the sightings, and they would not pass muster as a sight or sound record for any bird species, let alone IBW. There may be some important observations here, but until they are vetted by a review process, they represent unsubstantiated claims from a single individual, and do not meet the standards of evidence for occurrence of IBW. I note that the Florida team apparently concluded that the author's sighting there was not valid, as they do not include it among the 7 sightings they report for the 06-07 search.

I am very surprised that the author does not even mention the 1999 report of IBW in the Pearl River area by David Kulivan. This is widely considered a fairly credible sighting, and lead to an exhaustive search of the area by the Cornell team. I would think this is relevant background to this report, which is of course from the same area.

The "through the gap" footage is presented as some of the best evidence the author obtained, and he focuses attention on the blurry pattern of black and white in the center of the frame that he argues is an IBW. No mention is made of a second, similar black and white pattern above the first one. Is this supposed to be a second IBW or something else?