All that distinguishes the ivory-billed woodpecker from the pileated is about an inch in height and subtle differences in plumage, but for the past century their fates could not have been more different. Why did one falter while the other flourished, and will either hold its own in the future?
Last April, within days of the announcement of the ivory-billed woodpecker's resurrection in Arkansas, reports of fresh sightings began pouring into the Cornell Laboratory of Ornithology and other institutions involved in the tracking effort. Suddenly it seemed these avian celebrities were everywhere, including suburban neighborhoods far beyond the southeastern and lower Mississippi Valley states that make up the ivory-bill's historic range. By mid-July the lab had received nearly 2,000 phone calls and e-mails describing sightings, says Ron Rohrbaugh, the leader of Cornell's ivory-billed woodpecker recovery project. “We've had reports of ivory-billed woodpeckers in people's backyards from Michigan to Maine.”
While Rohrbaugh and his colleagues are committed to scrutinizing all reports from appropriate regions and habitats, they recognize the overwhelming odds that any big, black-and-white-winged, red-crested woodpecker seen in the United States today will be a pileated. Indeed, some experts believe it's possible that the Arkansas birds were pileateds, not ivory-bills, a position vigorously disputed by those who made the observations.
It's no surprise that there's uncertainty and debate, since the two woodpeckers share many physical attributes. “They can be a real challenge to distinguish in a quick glimpse if one is not intimately familiar with them,” says Jerome Jackson, a Florida Gulf Coast University professor who has studied both species. “The ivory-bill is slightly larger than the pileated, but there's no way that one could be certain of identity on the basis of size alone if [the bird] is seen in a fleeting glimpse or at much of a distance.” Ticking off the similarities, he notes that both are mostly black, have a head crest and a white stripe down each side of the neck, and can fly on either a level flight path or with long undulations. He also points out that sunlight glinting off a pileated woodpecker's dark bill can lend it an ivory-white paleness.
In June the Cornell lab launched a website—including range maps, habitat descriptions, field marks, and photographs—designed to help people differentiate between the two species. The decrease in the number of obviously erroneous reports since then pleases Rohrbaugh, but he's not dismissive of the smaller woodpecker. “The pileated is certainly a beautiful bird and something I think everyone enjoys seeing,” he says. “It can be a spectacular sighting. I don't want to take anything away from that.” Yet somehow there is a tendency to take these birds for granted, especially where they are relatively numerous and regularly seen.
In North America the 19-inch-long pileated is the third-largest member of the woodpecker family, exceeded in size only by the 24-inch-long imperial—a resident of Mexico's Sierra Madre Occidental and once the largest woodpecker in the world but now believed to be extinct—and the 20-inch-long ivory-bill.
The pileated woodpecker's range encompasses most forested areas in the eastern half of the continent from the Gulf of Mexico to well north of the Great Lakes, then cuts west across central Saskatchewan and extends through much of Alberta, British Columbia, and the northwestern U.S. states. Field guides list it as “uncommon and local” in most parts of its range, and “common” in the Southeast, but that was not always the case. Anecdotal accounts indicate that pileated woodpeckers became noticeably scarcer throughout eastern North America (and possibly in the West as well) during the 1800s and early 1900s, a time of extensive logging and land clearing.
“People thought that the pileated might easily go the same way as the ivory-billed woodpecker,” says Jackson. But by the 1930s, when second-growth forests were starting to mature, it was apparent that pileated numbers were on the rise again. Breeding Bird Survey results for 1966 to 2004 show a general increase in pileated populations in all regions, with particularly strong gains in the northeastern states and around the Great Lakes. “They're alive and well,” Jackson declares, adding that in the future we can expect to see even more of these birds in urban environments, as trees planted in backyards, parks, and greenbelts grow older and bigger.
Why then has the ivory-billed woodpecker not made a similar comeback? How could two species that lived side by side in the southeast corner of the continent for millennia and also seem to have so much in common have fared so differently over the past two centuries? It was this conundrum that, in the 1930s, prompted the National Audubon Society to send Cornell University graduate student James Tanner out into the bottomland hardwood forests of Louisiana to study one of the last known ivory-bill populations. An important objective of this initiative was to learn why the ivory-bill might not be able to persist alongside its smaller relative the pileated. The simple answer Tanner returned with was that the ivory-bill was more of a specialist in its feeding habits and, as a result, needed larger areas of more pristine habitat.
Based on a careful examination of the meager historical record and his own field data, Tanner estimated that the maximum density of ivory-billed woodpeckers in optimal habitat was one pair per six square miles—roughly the same as the density of the population he studied in the Singer Tract in Louisiana. In contrast, an average square mile within the Singer Tract supported six pairs of pileateds, making this species 36 times more abundant. (Red-bellied woodpeckers, at 21 pairs per square mile, were 126 times more abundant than ivory-bills.)
Tanner's calculations tell us that even in their heyday, ivory-bills were spread thinly across the landscape and were outnumbered by pileated woodpeckers, though there is no way of knowing exactly how many of either species once existed. Yet both were successful as long as their environment remained stable. What changed their lives and sent one speeding down the road to extinction was the bonanza era of logging, which lasted in the Southeast from about 1870 until the early 1940s, when the supply of timber effectively ran out. By the time the sawdust settled, all that was left was a scattering of old-forest islands amid a sea of fields, towns, and young stands of second-growth trees. The effects on both the ivory-billed and the pileated woodpecker were severe but not equally so, especially when it came to finding sustenance.
Tanner devoted much of his three years of fieldwork to studying his subjects' diet and feeding habits, and in his final report he compared these with the pileated woodpecker's. The key difference in terms of species survival, he concluded, was that ivory-bills depend on a food supply that is very irregularly distributed and available for only a short time in any one place, whereas pileateds have a more enduring and widely available prey base.
Ivory-bills specialize in feeding on wood-dwelling beetle larvae, particularly the thumb-size, calorie-packed larvae of cerambycid (or long-horned) beetles, which live beneath the bark of large, recently dead trees. The birds use their powerful, chisellike bills to knock and pry off the tight bark, stripping trunks and branches bare and leaving characteristic cross-hatching marks on the wood. The only other North American woodpecker equally capable of exploiting this rich food source—but in a range that did not overlap with that of the ivory-bill—was the closely related imperial.
Ivory-bills with dependent offspring require a generous supply of high-quality food within easy flying distance of their nest, a situation found only in old-growth forests with extensive stands of big trees that have been dead for less than two years. In pre-settlement times, finding such stands was no problem. When the food ran out in one area, frequent wildfires, flooding, and hurricanes ensured that new foraging areas were never far away. By the early 1900s, however, there were few remaining old-growth forest patches large enough to support a breeding pair of these birds and fewer still that could maintain a viable population.
Pileated woodpeckers are much less constrained in their foraging. As Tanner put it, they can “feed upon a tree until it has almost returned to earth.” In the past these woodpeckers were commonly known as “logcocks” because they spend so much time tearing apart rotting logs in search of ants and beetle larvae. They also find good feeding opportunities in standing dead trees through all stages of decay and in live trees that have been invaded by carpenter ants, one of their preferred prey species. Once a pileated woodpecker locates a productive carpenter ant colony, it will return repeatedly to feed there over a period of months or years, gradually enlarging and deepening its distinctive rectangular foraging holes as it excavates into the farther galleries.
Tanner occasionally saw ivory-billed woodpeckers foraging in a manner similar to pileateds, but the two species paid little attention to each other, even when feeding in the same tree. His conclusion was that the ivory-bill had no real competitors for food. Others, however, have challenged this theory. Lester Short, curator emeritus at the American Museum of Natural History and a leading authority on woodpeckers, wrote in his 1982 book, Woodpeckers of the World, that he was “pessimistic about chances for establishing a viable Ivory-Billed population in the presence of Pileated Woodpeckers” because of feeding competition. In Jerome Jackson's opinion, there's validity in both views. He believes there was probably limited foraging overlap between the two woodpeckers under natural conditions, but habitat loss may have forced ivory-bills to rely more on atypical prey, including the ants and smaller beetle larvae that pileateds are so well adapted to finding and capturing. “In such a situation,” he argues, “the pileated probably had the advantage—a possible factor contributing to the decline of the ivory-bill.”
While the question of potential competition between these two woodpeckers may never be settled, we do know without a doubt that ivory-bills were profoundly dependent on vast areas of what Tanner referred to as “virgin” or “primitive” forest—the only habitat endowed with sufficient quantities of suitable food, as well as a good selection of dead trees that were large enough to accommodate nest cavities with an interior diameter of up to 10 inches. Pileated woodpeckers, on the other hand, can get by in environments that have been altered by humans, provided those environments retain certain components characteristic of old-growth forest, namely plenty of dead or dying, large-diameter trees—for nesting and roosting—and ample quantities of decaying woody debris on the ground for foraging.
Richard Conner, a research wildlife biologist with the U.S. Forest Service's Southern Research Station, says that nowadays in the Southeast, pileated woodpeckers are “as common as they can be for a species that has a large territory” and that their future looks secure under current conditions. What worries him is the trend toward cutting trees at a very young age on private industrial forestlands. In this region, 35-year-old pine snags are usually just large enough for nest-excavating pileated woodpeckers. “If you go to a 15- to 25-year rotation for pulpwood,” Conner cautions, “you're not growing big enough trees for pileateds.”
Meanwhile, his Forest Service counterpart in Oregon has a different concern. Evelyn Bull, a research wildlife biologist, says the prescribed burning of snags—dead, standing trees—and downed woody debris to prevent large forest fires is currently “one of the biggest threats to pileateds in the interior Pacific Northwest, because the very things they need to survive are being removed.” The problem, she says, is lack of control. When fire is used as a forest management tool, it can become difficult to retain pileated nest and roost trees and the logs and stumps that serve as the birds' larders.
Bull's research shows that pileated woodpeckers may remain in areas that have had extensive burns, but they may fail to reproduce because there is not enough food to raise a family. “It certainly has the potential to negatively affect pileated populations over the long term if standing and downed structures are not retained,” she says. This is a timely warning, since prescribed burning is among the practices promoted by the Bush administration's controversial Healthy Forest Initiative, which is ostensibly intended to prevent wildfires and insect infestations.
As things stand today, very few, if any, of us will ever have the privilege of seeing an ivory-bill. But the pileated is still with us, despite our carelessness. The fate of the one gives us all the more reason to treasure each sighting of the other—whether it's in the wilderness or in a wooded urban enclave, perhaps near you—a startlingly large, black woodpecker swooping through the trees, its red crest burning like a flame and kindling our imaginations.
Frances Backhouse writes about natural history and environmental issues from her home in Victoria, British Columbia. She is also the author of the newly released Woodpeckers of North America, published by Firefly Books.
© 2005 National Audubon Society
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