The Ivory-billed Woodpecker and the Spectrum of Extinction
By Jay Tischendorf DVM
As a starting point for this musing, I hope readers will agree that many facets and phenomena of life and our experience on earth occur on a spectrum. For the sake of this article, let’s apply this concept to the subject of extinction. This won’t be a hardcore scientific treatment, or entail complex biostatistics, but let’s use a simplified spectrum to try to characterize how final any decrees or pronouncements of extinction truly are.
Before we go further, though, let’s also more or less agree that recognition of extinction for a species or subspecies is reflective of, typically, a consistent process over time where declining abundance of the creature is noted and eventually the species is eventually officially determined, or at least widely accepted, to have vanished.
To get started, then, at the left end of our imaginary “Extinction Spectrum” let’s place creatures that we are quite confident are definitely, definitively, and irrevocably extinct. These species would for example include T. rex, the stegosaurus, wooly mammoth, dodo, great auk, and passenger pigeon. Clearly the bulk of species thought to be extinct are, with no question, truly and unmistakably extinct. So, there’s, sadly, going to be a big clump of long gone creatures never-to-be-seen-again at that end of the spectrum
As we move to the right along this spectrum, we can add other species or subspecies that are almost assuredly correctly believed to be extinct. We can and no doubt will likely discuss and argue over which species and subspecies fit best here and why, or how to rank and order them. That’s part of what is so captivating about this “Extinction Spectrum”: things aren’t always as black and white as they might seem. For example, one animal that might properly be discussed as we continue our journey to the right on this spectrum is the thylacine, or Tasmanian Wolf, which hopefully isn’t extinct but is widely agreed to be. In this same area of our spectrum lie other species which similarly are largely considered extinct and probably are, but whose status is uncertain or questioned. This includes, for instance, the Yangtze River Dolphin or Eskimo Curlew, since for both of these species there remains some seemingly legitimate lingering possibility of their continued existence.
Miraculously, though, far out on the extreme right end of our tragic Extinction Spectrum, even beyond these aforementioned mysterious “question mark” species, there lies a handful of the world’s most unique species. These are species that have been declared extinct but which have then actually been rediscovered, incredibly resurrected, if you will, from the abyss of absolute extinction. For these species, in fact, the probability that their reported extinction was actually and unequivocally final is, at least for now, zero. This group of so-called Lazurus species includes the Jamaican Iguana, Stresemann’s Bristlefront, the Coelacanth, Bermuda Petrel, Fernandina Giant Tortoise, Wallace’s Giant Bee, Chacoan Peccary, Pinocchio Lizard, New Guinea Big-eared Bat, Australian Night Parrot, Zapata Rail, Kashmir Musk Deer, Jerdon’s Babbler, Jerdon’s Tree Frog, Blue-eyed Ground Dove, Tachira Antpitta, Goblin Shark, Omura’s Whale, Black Kokanee, Pygmy Tarsier, and others. And, equally amazingly, the list continues to grow! For just recently, here in 2021, both Swinhoe’s Soft-shelled Turtle and the Great Fox Spider of Britain have been rediscovered.
Where should one best place the Ivory-billed Woodpecker along this spectrum? On the same extreme with T. rex and pterodactyls? Or perhaps closer to the thylacine and Yangtze Dolphin, or even—for those who believe the evidence for its continued existence is indisputable—next to a Lazarus species such as the “Sengi,” or Elephant Shrew, which was just rediscovered in Djibouti after not being seen for about 50 years?
The answer to this is of course subjective. But—definitively extinct, probably extinct, or only possibly extinct—if we were to try this case in a court of law, is it reasonable to think that a rational, freely thinking, neutral, and objective jury would conclude there is enough circumstantial evidence that Campephilus principalis might still exist despite proclamations of its extinction in the 1940s?
I think so.
There’s an old saying in statistics: “Absence of evidence is not necessarily evidence of absence.”
Now, in the case of the Ivory-billed Woodpecker, there actually is evidence. In fact, some people might go so far as to say that the evidence brought to light in recent decades even has valid scientific weight. This includes multiple observations by credible ornithologists or other scientists, photographs which are unlikely to depict any other creature and unlikely to have been faked or otherwise contrived, an Ivory-billed Woodpecker feather from a cavity, highly suggestive videos, and hours’ worth of numerous recorded vocalizations with acoustic parameters virtually identical to those of known ivorybills. Of course, none of this is acceptable to the institution of Science as indisputable proof of the woodpecker’s continued existence. But, on the other hand, just because Science doesn’t accept something doesn’t mean it isn’t true. After all, neutrinos, the Law of Gravity, gorillas, and DNA were all around before Science recognized they existed.
Returning to our spectrum, what can we learn from those rare species that, like the mythical Phoenix rise from their ashes and comprise—extinction fail!—the far and seemingly impossible extreme of actual rediscovery? Qualitatively, at least, it seems that a significant number of these species—birds, mammals, and other groups included—share several key similarities that if applied to other supposedly extinct creatures may provide some hope that the latter in fact are not dead and gone. One of these similarities is habitat. Consider how many rediscovered species spend their lives in areas that are inhospitable and almost inaccessible—pelagic environments, jungles, thickets, arboreal habitat, vast untracked grasslands, rugged mountains, caves, deep-sea zones, and so on.
A second notable commonality among many rediscovered species is this: They utilize burrows. And, when one discusses burrows, I too think it is fair to also lump in cavities….
Lastly, another characteristic of many Lazurus species is that prior to their presumptive extinction they were little studied and understood.
Intriguingly, our elusive, mystical Ivory-billed Woodpecker embodies not just one but all three of these factors, inhabiting as it did/does the remote, inhospitable, and oftentimes nearly inaccessible wilderness of southern hardwood swamps, and also necessarily vanishing into cavities for nesting and roosting. And, as other ivorybill believers have compelling argued, the primary, peer-reviewed literature on the species is almost nonexistent, too. How well do we truly know this bird?
It is worth noting that other commonalities among many Lazarus species include a high degree of ecological specialization and, even under optimal conditions at their peak numbers, a relatively low-density population structure. Here again, our ivorybill shares these qualities too. In short, when we look at characteristics common to many Lazarus species, the ivorybill is a match on virtually all counts. Surely if there was a poster child for the possibility of continued existence, wouldn’t it be a creature such as this?
A wonderful living example of this is conveniently provided by the enigmatic Black-footed Ferret. Living clandestinely amidst the untrammeled grassland prairies of the American Outback, this mustelid spends most of its life underground in the burrows of its sole prey source, the prairie dog. So secretive and elusive is this captivating species, which feeds exclusively on prairie dogs, that it has been declared extinct and then astoundingly rediscovered and resurrected at least two if not three times since it was first described by Science almost 200 years ago.
Whatever side of the fence the reader finds themselves on in regard to the ivorybill, keep in mind that the ivorybill has only been considered extinct for 75 years or so. The Australian Night Parrot was resurrected after roughly 77 years of presumed extinction. Just recently, the Wondiwoi Tree Kangaroo—having been MIA for 90 years—has been rediscovered. So too has the Black-browed Babbler, which reappeared in Indonesia after a 170 year hiatus. And, for even greater perspective, the Bermuda Petrel, or Cahow, was considered dead and gone for some 330 years before it was serendipitously rediscovered.
My hope is that we can document the Ivory-billed Woodpecker sooner than that. But, those who follow this mystery should be resolutely strapped in for the long haul and rough ride. In the meantime, if you’re a gambler, I’m convinced it’s going to pay to bet on black. And white. After all, those are the colors of this magnificent, confounding, and enigmatic bird.