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Professor Geoffrey Hill, leader of the Florida search for the Ivory-billed Woodpecker, tells why we should continue looking for the bird
Professor Geoffrey Hill, leader of the Florida search for the Ivory-billed Woodpecker, tells why we should continue looking for the birdHeavy-handed searches in Florida and Arkansas have failed to gather definitive evidence, but multiple, simultaneous sight records and sound detections should not be dismissed casually.
Published: October 25, 2007 In January of 2006, in an early draft of my book Ivorybill Hunters , I wrote:
There have been two professional and very thorough searches of large swamp forests in the southeastern U.S. in the last 50 years -- the Pearl River in Louisiana in 2001-2002 and the Cache and White Rivers in Arkansas in 2003-2005. I think we can confidently state very little about the present distribution of Ivory-billed Woodpeckers in the U.S., but thanks to the Louisiana and Arkansas searches, we can state with great confidence that there exist no resident populations of Ivory-billed Woodpeckers in these areas. They can be taken off the board as sites potentially harboring ivorybill populations. There is no way the massive searches along the Cache, White, and Pearl Rivers missed entire populations of ivorybills. Further searches would be a waste of resources. Spending an additional penny on the recovery of an ivorybill population in Arkansas when not a single individual can be located makes no sense at all.
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I cut the passage in later edits, but I find it very humbling to go back and reread my words. When I wrote them, we were having regular encounters with birds that looked and sounded like Ivory-billed Woodpeckers (Campephilus principalis) near the mouth of Bruce Creek along the Choctawhatchee River in the Florida panhandle, and it seemed that definitive documentation was certain to come soon. Now, in October 2007, following the logic in the above paragraph, I would have to add the Choctawhatchee to the list of areas that have been the focus of intensive searches that have produced no definitive proof of the existence of Ivory-billed Woodpeckers. The Congaree River basin in South Carolina would have to go on the list as well.
Was I correct in my assessment? Is it really time to conclude that no breeding ivorybills persist in the White, Cache, Pearl, Choctawhatchee, or Congaree River swamps -- areas that contain some of the largest tracts of mature swamp forest in the Southeast and have been the centers of the most convincing recent detections of Ivory-billed Woodpeckers?
Having just completed a multi-person, year-long, hundred-thousand-dollar search of the forested wetlands along the Choctawhatchee River, I must reconcile our claim that Ivory-billed Woodpeckers persist with our failure to gather definitive evidence for their existence. There are two possible explanations. One must be correct, but neither is easy for me to accept. |
Explanation No. 1: Ivorybills do not exist
The first explanation is that we were wrong in our claim, and Ivory-billed Woodpeckers do not exist in the forests along the Choctawhatchee River. Of course, this means the birds that we saw and identified as Ivory-billed Woodpeckers were something else, and the sounds that we heard and recorded and attributed to ivorybills were produced by something other than Ivory-billed Woodpeckers.
As one of the observers who reported seeing an Ivory-billed Woodpecker along the river, and as a person who has heard both double-knocks and kent calls on multiple occasions, I don't easily accept that all the sight records and sound detections were mistakes. The sightings by Tyler Hicks in particular are hard to dismiss as misidentifications, given the multiple diagnostic field marks he observed.
During a May 2005 sighting, when Hicks observed a bird in focus in his binoculars, he noted three independent plumage features that separate Ivory-billed Woodpeckers from Pileated Woodpeckers (Dryocopus pileatus): a white trailing edge on the upper wing, bold dorsal stripes, and a black crest. He also noted distinctive size, shape, and flight behavior.
In December 2006, Hicks observed a bird at close range perched on a tree and noted four diagnostic features of a female Ivory-billed Woodpecker: extensive white on folded wings, dorsal stripes, a black crest, and a striking ivory-colored bill. Hicks is an experienced birder, good enough to have served as a professional birding guide. It seems very unlikely he would perceive an entire suite of traits on a bird that did not exist. Moreover, his sighting was in an area that in December 2006 was more than two kilometers from the location of any previous Ivory-billed Woodpecker sightings. In the four months following his sighting, however, there were five more Ivory-billed Woodpecker sightings in the area, and automated sound recorders captured dozens of putative kent calls and double-knocks at the location. Hicks's sighting anticipated the location of greatest Ivory-billed Woodpecker activity in 2007.
During additional sightings of Ivory-billed Woodpeckers, observers noted fewer diagnostic features but still saw enough to be certain that they had seen an ivorybill. In total, we now have 21 sight records from competent birders of Ivory-billed Woodpeckers along the Choctawhatchee River. |
Double-knocks and kent calls
The conclusion that ivorybills do not exist along the river also means all the double-knocks and kent calls that my research team, visiting birders, and I heard, and that Dan Mennill and his sound team at the University of Windsor recorded, were produced by something other than Ivory-billed Woodpeckers. To date, no convincing argument has been made for alternative sources for either the double-knocks or kent calls that we recorded.
The bleating of young white-tailed deer, proposed by Collinson to be the source of kent calls, is not a good match to the sounds we heard and recorded. Puddle ducks such as Gadwall, which, as Jones et al. reported, produce occasional double-bangs with their wings, are not present along the Choctawhatchee River as more than rare transients. A crew of experienced searchers/birders recorded no Gadwall and only a handful of individual puddle ducks in nine months of daily searching over two years. Whatever is making the sounds is strictly diurnal. Mennill's team searched 1,500 hours of nighttime sound recording and flagged zero putative double-knocks or kent calls.
We published putative Ivory-billed Woodpecker sounds recorded from January to April 2006 in the journal Avian Conservation and Ecology - Écologie et Conservation des Oiseaux, which has a format that accommodates critiques and reinterpretations of published papers. To date, no one has published a reinterpretation of the sounds that we presented as evidence. Failure to identify an alternative source does not mean that the sounds were made by Ivory-billed Woodpeckers, but at present, ivorybills are the only native animal known to produce such double-knocks or kent calls.
The large holes in trees and scaled bark that we also find in the forests along the Choctawhatchee River provide indirect evidence for the presence of ivorybills, but unlike the recorded sounds, these features can be reasonably attributed to a common native animal -- the Pileated Woodpecker. We need more study of both cavity sizes and bark scaling to better interpret such evidence.
Taken individually, the sight records, the sound detections and recordings, the large cavities, and scaled bark provide a substantial body of evidence for the existence of ivorybills along the Choctawhatchee, but it is the co-occurrence of multiple types of detections that is hardest to dismiss.
Pileated Woodpeckers might look similar to Ivory-billed Woodpeckers and they might, rarely, make two knocks on wood, but they never make vocalizations that would sound like a kent call and they've never been reported to give series of double-knocks. Blue Jays might sometimes make kent-like sounds, but they don't knock on wood and they look nothing like Ivory-billed Woodpeckers. |
Simultaneous rare events
If all of our detections are mistakes, including misidentifying Pileated Woodpeckers as Ivory-billed Woodpeckers and misidentifying the sounds of Blue Jays as Ivory-billed Woodpecker kent calls, then mistaken sound detections should occur completely independently of mistaken sightings. The potential sources of ivorybill-looking things and ivorybill-sounding things are distinct.
When Hicks observed a female Ivory-billed Woodpecker at a distance of about 12 meters [40 feet] and saw diagnostic plumage features on December 24, 2006, he was drawn to the spot by multiple double-knocks and kent calls that two other observers had also heard.
How do we simply dismiss an encounter with an animal that involves a positive visual identification by a skilled birder based on feather and bill coloration coupled with clear audio detection of two different and distinct sounds that should be produced only by that bird species? We need to propose two simultaneous rare events -- a Blue Jay giving kent-like calls (which I have never heard despite a lifetime of listening to Blue Jays in the South) and a Pileated Woodpecker giving a series of double-knocks (which I've also never heard despite a lifetime of listening to Pileated Woodpeckers in the South) -- just as Hicks misidentified a pileated as an ivorybill despite a clear look at the bird at close range.
Similarly, when I watched a large, long-winged woodpecker with bright white trailing edges on its dorsal wing surfaces fly away from me in January 2006, I heard a clear double-knock to my right after I had positively identified the fleeing bird as an Ivory-billed Woodpecker. What are the chances that just as I was misidentifying a Pileated Woodpecker as an Ivory-billed Woodpecker, I would hear another pileated give a double-knock? |
Moreover, within three hours of my sighting, sound recorders set up 200 meters from the location of my sighting recorded two double-knocks, and in the two days immediately preceding my sighting, unbeknownst to me at the time, listening stations at the location of my sighting recorded two and ten double-knocks, respectively. On the day after my encounter, listening stations recorded three kent calls and five double-knocks. If my sighting of an Ivory-billed Woodpecker was a misidentification, it is quite a coincidence that machines recorded many putative Ivory-billed Woodpecker sounds only at that location in the days surrounding my sighting.
We now have numerous occasions in which both kent calls and double-knocks were recorded at the same time and place, and occasions in which machines recorded putative kent calls or double-knocks in the same time and place that humans thought that they heard or saw Ivory-billed Woodpeckers. I have yet to hear a rational explanation for what might temporally and spatially link ivorybill-looking things with ivorybill-sounding things except a living Ivory-billed Woodpecker. |
A bird captured on videotape
Finally, in May 2006 Brian Rolek saw a large bird that he positively identified as an Ivory-billed Woodpecker fly across a narrow water channel in front of his kayak. He clearly saw a broad white trailing edge on the dorsal plumage of a large black bird, and he watched it swoop to the side of a tree like a woodpecker. I was behind him in a different boat and did not see the bird, but a video camera mounted on the front of my boat captured the event.
In reviewing the videotape, we can see the bird. It is a large bird that appears to be a woodpecker with extensive white on both the dorsal and ventral wing surfaces. It appears to have too much white to be a Pileated Woodpecker, and the white on the dorsal plumage seems to be on the trailing edge of the wings.
The bird in the video cannot be identified positively as an ivorybill, but all plumage features and behaviors are consistent with Ivory-billed Woodpecker, and some plumage features seem inconsistent with Pileated Woodpecker. What are the chances that the one time Rolek misidentified a Pileated Woodpecker as an Ivory-billed Woodpecker on camera, we would capture on video a bird that seems consistent with Ivory-billed Woodpecker but inconsistent with Pileated Woodpecker? |
Explanation No. 2: Ivorybills are hard to photograph
If we find these layers of evidence too substantial to dismiss and conclude that Ivory-billed Woodpeckers persist along the Choctawhatchee River, then we are left with the second explanation for our failure to get definitive evidence for their existence: The birds are so elusive that teams of searchers are incapable of getting a clear image of one.
In April 2006, I had no trouble explaining how we missed getting a clear photo of an ivorybill the previous year -- Rolek and I were the primary searchers, and neither of us is very skilled at using video cameras; we didn't run cameras from the front of our boats often enough; and we didn't have remote cameras.
Now, at the end of a 2007 search in which we had more than a dozen people searching full-time for five months and we deployed 19 remote cameras, reasons for our failure to get clear photos do not come so easily. However, I think that three widely recognized characteristics of Ivory-billed Woodpeckers can reasonably explain why the species is so hard to see and photograph along the Choctawhatchee River and elsewhere in its fragmented range.
1. Ivory-billed Woodpeckers in this area are silent most of the time.
Sounds are almost always what lead birders to woodland birds. When Downy (Picoides pubescens) and Hairy Woodpeckers (P. villosus) go silent in eastern deciduous forests in late summer and fall, the birds can be hard to find even in areas where they are common. In the spring, when they make noise, the same number of downys and hairys can be conspicuous.
2. If Ivory-billed Woodpeckers exist, they exist at very low density.
I speculated in my book Ivorybill Hunters that there could be tens of pairs of ivorybills along the Choctawhatchee River. My assessment was based on our repeated sightings of ivorybills near the mouth of Bruce Creek and a speculative extrapolation to other areas of the swamp where we had spent little time. I no longer believe this speculative estimate is accurate. There are probably only a few Ivory-billed Woodpeckers in the approximately 60,000 acres of forest along the river. A mostly silent, very scarce bird would not be encountered very often even if the birds flew randomly through the forest paying no attention to people.
3. Finally, our observations suggest that Ivory-billed Woodpeckers in the Florida panhandle are extremely wary of people.
When Ivory-billed Woodpeckers detect a person, they move away from him or her. First they appear to shift to the side of the tree away from the approaching person. Then they fly directly away, keeping the tree between themselves and the human. This behind-the-tree behavior means that even on the rare occasion when an observer gets close to an ivorybill, he or she typically won't see the bird when it flies off. Ivorybills don't need any supernatural attributes to pull off their vanishing acts. All they need are sharp eyes, acute hearing, and a strong desire to get away from humans. |
Are additional searches worthwhile?
The recent efforts by professional ornithologists and wildlife biologists to document the existence of Ivory-billed Woodpeckers has brought the status of the species in North America to a critical juncture. A large amount of money and effort has been expended. A substantial body of evidence has been gathered that at least a few Ivory-billed Woodpeckers persist, but no definitive proof has been produced. The failure has understandably led to skepticism among ornithologists and birdwatchers. It has also led to debate about whether investing more time and effort in a search for ivorybills is worthwhile.
Having led a major expedition to find and photograph the ivorybill, my opinion is that the bird is worth more time and support. We have learned much from past efforts about methods that do not work. Heavy-handed, straight-at-the-birds searches do not hold much hope of success. The approach failed in Arkansas, and it failed in Florida. The birds are simply too wary of humans and retreat from the heightened human activities that come with large searches.
I think that the best hope for photographing an Ivory-billed Woodpecker is by means of automated surveillance once a location with birds is discovered. Camera and battery technology has advanced far enough just in time to make such an effort feasible. Remote cameras collecting very high-resolution images could be pointed at cavities, feeding trees, or potential flyways and allowed to click away for days.
The commercially available Reconyx cameras that we deployed in 2007 were, in my opinion, not quite good enough to get the job done. They had only 2.5x telephoto lenses, meaning that they had to be positioned so close to a cavity or feeding tree that they likely created a disturbance that reduced the chances of an ivorybill landing in front of them. New automated cameras can be constructed with 10x or even 20x lenses; they could be placed far back from a cavity or feeding tree and not encroach on the birds. |
The U.S. Fish and Wildlife Service doesn't rule out developing new cameras, but this winter, it plans to rely on expert birders and helicopters in the search for the woodpecker. Read more in this BirdersWorld.com exclusive: Ideal Remote Camera is Just an Idea |
Image resolution also proved inadequate. In November 2006, we captured an image of three flying birds. They were consistent in shape with Ivory-billed Woodpeckers, but the image lacked the detail needed for a positive identification. Had we been using a camera with a tighter zoom shooting higher-resolution images, and in color rather than black and white, we may well have gotten a definitive image of an Ivory-billed Woodpecker from our 2007 effort. Or at least we would have known the identity of the three birds flying past the cavity.
Since several blocks of forest in the Southeast are now reported to host ivorybills, I think we need to give surveillance with remote high-resolution cameras a chance to succeed. Conducting camera surveillance would be much cheaper than deploying large search teams.
Along with a handful of bird species like the Passenger Pigeon and the Great Auk, the Ivory-billed Woodpecker is among the most important and widely known symbols of the unsustainable and irresponsible exploitation of the natural resources of North America. Passenger Pigeons, Great Auks, and Ivory-billed Woodpeckers were not wiped out by subsistence farmers trying to scratch out a living. They were not necessary casualties of the growth of western civilization in North America. There is no easy justification for their slaughter. Each was the target of mass exploitation for the profits or enjoyment of wealthy corporations or individuals. I find it hard to attribute the extinctions and extirpations of these species to anything but greed. Populations of these species were treated as commodities and ruthlessly converted into cash.
There is no hope of bringing back the Passenger Pigeon or Great Auk; these birds now exist only as a few study skins and skeletons. In keeping with its reputation for independence and defiance of human subjugation, the Ivory-billed Woodpecker appears to have clung to a tenuous existence in a few locations. Given our sad history of association with this bird, we owe it a chance to be documented and protected. |
Literature cited
Collinson, J. Martin. 2007. Video analysis of the escape flight of Pileated Woodpecker Dryocopus pileatus: Does the Ivory-billed Woodpecker Campephilus principalis persist in continental North America? BMC Biology 5: 8. See also A new challenge to the Luneau video, Birder's World Field of View, posted March 14, 2007.
Hill, Geoffrey E. 2007. Ivorybill Hunters: The Search for Proof in a Flooded Wilderness. Oxford University Press.
Hill, Geoffrey E. (February) 2007. The other guys: The author of A Red Bird in a Brown Bag describes how he found an Ivory-billed Woodpecker in a Florida swamp. Birder's World 21(1): 22.
Hill, Geoffrey E., et al. 2006. Evidence suggesting that Ivory-billed Woodpeckers exist in Florida. Avian Conservation and Ecology - Écologie et conservation des oiseaux 1(3): 2.
Hill, Geoffrey E., and Dan Mennill. Ivory-billed Woodpeckers in the Florida Panhandle (webpage).
Jones, Clark C., et al. 2007. Similarities between Campephilus woodpecker double raps and mechanical sounds produced by duck flocks. Wilson Journal of Ornithology 119(2): 259. |
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