Woodpecker nest holes are worthwhile items of actual property that could be utilized by a whole bunch of different species over a few years. Researchers are utilizing the idea of “nest webs” to grasp how this worthwhile useful resource passes from one proprietor to the subsequent.
From the Spring 2025 situation of Dwelling Chook journal. Subscribe now.
When evening falls within the forest, most birds tuck into nooks the place they will really feel safe—the V-shaped intersection of two tree boughs, a cluster of dense branches. Some could take to the eaves of close by homes. Brown Creepers discover a piece of shaggy bark to wedge their our bodies below.
And plenty of birds—generally greater than half the species in a given woodland—stow themselves safely into a spot we people hardly ever (and barely) get to see: inside the outlet of a tree.
Whether or not it’s a fraction of forest bordering an city neighborhood, or an old-growth stand that’s been regenerating itself for millennia, tree cavities are a typical and essential a part of habitat in each forest panorama.
In the case of a comfy house, few locations can ship like a tree cavity, says Kevin McGowan, teacher for the Cornell Lab of Ornithology Chook Academy course The Fantastic World of Woodpeckers. McGowan says an enormous a part of recognizing the contribution of woodpeckers to an ecosystem begins with understanding the worth of a gap.
“Holes in timber make nice houses for every kind of animals,” says McGowan. “They’re off of the bottom, simpler to defend from predators, they keep dry when it rains. It makes them an ideal place to roost and to lift younger.”
A examine printed within the journal Range and Distributions in 2017 discovered that practically 20% of all chicken species around the globe depend on tree cavities for roosting or nesting, and a subsequent evaluation discovered that there are some areas of the world the place practically all cavities occupied by birds are made by woodpeckers.
In North America particularly, scientists are discovering that the nest holes excavated inside timber provide essential protected harbors utilized by dozens of species of birds, mammals, reptiles, and bugs—all thanks to a couple VIPs : Very Vital (Wooden)Peckers.
Flicker Nests Have Widespread Enchantment
Kathy Martin started learning woodpeckers and different cavity-nesting species within the mid-Nineties, when she was a newly minted professor of forest science on the College of British Columbia. She had an concept that woodpeckers would have tales to inform concerning the well being of forest ecosystems, and their skill to remain wholesome within the face of timber harvests, at a time when logging pursuits have been sizing up British Columbia’s huge inside forests.
Thirty years in the past “there was a real environmental feeling within the trade,” Martin says. “[Timber] firms have been fascinated with having ecologists weigh in on the administration of their lands—individuals who would inform the actual story and never simply say that the whole lot is ok.”
Woodpeckers have been a logical group to check, she says: “The woodpeckers have been … those that you’d predict could be very delicate to this type of harvest,” together with the selective logging of mature timber for the forest trade.
Over the primary two years of learning the organic communities in these combined Douglas-fir forests in western Canada, Martin and her analysis workforce recorded 32 chicken species that used tree cavities, together with major excavators like woodpeckers, which may drill into quite a lot of tree sorts in several phases of decay; weaker excavators like chickadees and nuthatches, which may solely excavate when the wooden is already rotting; and a bevy of secondary cavity nesters, that are birds that use preexisting cavities however don’t excavate their very own. The final group features a vary of species from Wooden Geese to Northern Home Wrens. Extra broadly, Martin estimates that round 30% of all forest chicken species in North America use tree cavities throughout their life cycle, whether or not nesting, hiding from predators, or simply discovering a heat roosting place to snuggle in on a chilly winter’s evening.
Martin and her workforce additionally recorded cavity use by 11 species of mammals, from purple squirrels to pine martens to fishers. In 1999 their examine, printed in The Condor, launched the idea of a nest net—a technique to describe the advanced system of animals that make, improve, and/or use tree cavities.
“It was based mostly on the thought of the meals net—you have got all these species which are linked collectively as a result of they’re sharing the identical assets,” says Martin, “and identical to in meals webs you have got your producers and your shoppers.”
Within the forests Martin research—combined Douglas-fir, which incorporates pine and spruce together with aspen, poplar, and birch timber—an important producer turned out to be Northern Flicker, which excavated practically 50% of tree cavities noticed. In line with a current estimate from the bird-monitoring alliance Companions in Flight, Northern Flicker is likely one of the most ample woodpeckers in North America. PIF estimates there are about 12 million glints throughout Canada, the U.S., and Mexico.
“I do assume the glints are so vital as a result of they’ve such a excessive abundance,” says Martin, “nevertheless it’s greater than that.” Except for making extra holes than some other woodpeckers, Martin says they make a gap that’s large enough for a lot of totally different species, however not so huge that the doorway gap feels unsafe.
In line with Martin’s analysis, flicker cavities emerged as an important nesting useful resource for songbirds comparable to Mountain Bluebirds, raptors comparable to American Kestrels, and waterfowl comparable to Buffleheads and Hooded Mergansers. Some chicken species even evict glints from their cavity nests.
“[Flickers] are type of wimps,” Martin says. “They don’t defend their cavities very nicely,” which suggests their nest holes are sometimes commandeered by extra aggressive birds like kestrels and starlings.
Importantly, solely round 10% of the cavities Martin and her workforce discovered have been so-called pure cavities—that’s, cavities not began by an excavator, comparable to a gap in a tree at a damaged bough brought on by wind or ice, then rotted out by micro organism or fungi.
However, Martin says, “a whole lot of these pure decay cavities that type in older timber and snags are crappy cavities … not as safe, not deep sufficient” for protected chicken nests.
In different components of the world, pure cavities that type with out assistance from woodpeckers play a a lot bigger function in forests. A examine printed in Biodiversity and Conservation in 2017 discovered that in temperate rainforests in Chile, 75% of nests utilized by secondary cavity nesters—birds comparable to Blue-and-White Swallow and the Patagonian Sierra Finch that don’t drill their very own cavities—have been situated in holes brought on by tree decay. The opposite 25% of nests have been in holes excavated by primary-cavity producers comparable to Magellanic Woodpecker and White-throated Treerunner, a nuthatch-like species.
That sample holds true for many locations outdoors of North America the place nest webs have been studied. In line with an evaluation printed in Frontiers in Ecology and Evolution in 2011, avian excavators (largely woodpeckers) produced round 77% of nesting cavities in North America, however solely a median of 26% throughout Europe and South America, and 0% in Australasia (the place woodpeckers don’t happen).
Kristina Cockle, lead writer of the examine, explains the discrepancy is partially because of the distinction in tree buildings around the globe. She says that in a lot of the world, forests are dominated by broadleaf timber with large branches: “When a big department breaks off … it has good potential to create an entrance to the already-decayed heartwood contained in the tree.”
Within the areas of North America and northern Europe the place these sorts of research have been finished, nonetheless, “timber are inclined to have a single important stem, with small branches that self-prune,” she says. When climate occasions knock branches off this kind of tree, it doesn’t have a tendency to show the heartwood and the tree can rapidly heal the wound—which suggests fewer alternatives for the formation of sizable pure tree cavities.
A Entrance-Row Seat
Virginia Tech researcher Jeff Walters has had a front-row seat to watching Very Vital Woodpeckers in a forest ecosystem for greater than three a long time.
Particularly he’s gotten accustomed to the haunts and habits of the Crimson-cockaded Woodpecker, an iconic chicken protected below the Endangered Species Act that makes its residing within the longleaf pine forests that dot the panorama from Virginia to Texas. As vital as woodpeckers are within the forests of western Canada, the woodpeckers of the longleaf pine forests are completely important, in line with Walters’s analysis. In a examine printed in The Condor in 2008, Walters and Virginia Tech PhD pupil Lori Blanc discovered that just about each single tree cavity utilized by birds and different creatures inside a longleaf pine nest-web group in northern Florida originated with a woodpecker—432 out of 433 cavities.
In conifer methods, Walters says, there may be “extra dependence on excavated cavities from woodpeckers in comparison with hardwood or tropical forests. Pine timber simply don’t produce a whole lot of … pure holes on their very own.” Pines additionally produce resin which will assist shield their wooden from an infection following damage.
Moreover, he says that longleaf pine methods have been clear-cut across the flip of the twentieth century, so there are a restricted variety of older, decaying timber and tree snags—locations which have gentle spots the place woodpeckers normally drill holes. Fortunately the Crimson-cockaded Woodpecker has a secret superpower that permits it to supply cavities in a means that the majority different woodpeckers can’t; they drill into stay timber.
“Crimson-cockaded Woodpeckers add an extra useful resource past the holes in lifeless pines, which is usually the place many of the motion is in nest webs in conifer forests,” says Walters.
Drilling right into a stay tree is something however straightforward. Most woodpeckers in North America can end a nest cavity in a matter of weeks, or perhaps a pair months. The typical Crimson-cockaded Woodpecker, however, takes years, generally as much as a decade or extra, to excavate a cavity in a stay tree. That’s as a result of chiseling away at stay wooden is troublesome, because of the dense sapwood layer below the bark that permits the tree to move vitamins from the roots to the leaves.
Crimson-cockadeds favor timber the place the sapwood is wholesome for a single motive, says Walters: “Resin wells.”
“If you happen to ever see an image of a Crimson-cockaded Woodpecker cavity that’s being actively used, you’ll see all this sap throughout it,” he says. The sappy coating across the nest holes creates a barrier of safety towards would-be predators. “Snakes can’t get by the sap.”
Walters’s analysis additionally reveals that glints once more play an vital function in longleaf pine nest webs, however usually they depend on Crimson-cockaded Woodpeckers to get issues began. Crimson-cockaded Woodpeckers and Northern Sparkles excavated essentially the most cavities (about 50%) that have been utilized by different cavity-nesting birds, and glints have been additionally the first enlargers of holes began by red-cockadeds that ultimately housed a few of the largest cavity-dwellers in longleaf pine forests—American Kestrels and Jap Screech-Owls.
There’s one other, much less seen, group of gamers within the longleaf pine nest net. Michelle Jusino started learning Crimson-cockaded Woodpeckers below Jeff Walters as a PhD pupil within the early 2010s and rapidly turned fascinated with a unique denizen of tree cavities: fungi.
“These birds have lengthy been thought to have an affiliation with one specific fungus [called Porodaedalea pini] as a result of that fungus causes heartrot,” says Jusino. However she says that the scientific data of that affiliation was based mostly on anecdotal commentary. “Generally after we see woodpecker holes, we see this fungus on the tree.”
So for her dissertation, Jusino designed a examine to seek out out precisely what fungi are current in woodpecker cavities, and the way they get there. She and her workforce of researchers drilled recent holes into residing longleaf pine timber and put galvanized metal screens over a few of the holes to maintain out Crimson-cockaded Woodpeckers. The opposite holes have been left open for red-cockadeds to entry.
Her outcomes, printed in Proceedings of the Royal Society B in 2016, discovered that each units of holes contained fungal communities that weren’t current at first, however that these communities have been very totally different from one another. The holes accessed by Crimson-cockaded Woodpeckers developed clusters of dozens of various fungi that have been similar to the fungal communities present in pure red-cockaded excavations.
“These birds are serving to facilitate these fungal colonizations, first by making holes, after which by transporting [the fungus] from one tree to a different,” says Jusino. “What that examine didn’t show was whether or not that fungus is basically serving to the chicken in return.”
Whereas Crimson-cockaded Woodpeckers overwhelmingly favor stay timber with wholesome sapwood, Jusino says they appear to have a desire for timber the place the heartwood is starting to decay. However the query stays: How are these woodpeckers figuring out such timber when there may be normally no proof on the skin? Jusino isn’t positive if red-cockadeds are sensing the rotting heartwood and accompanying fungi by odor, really feel, or another cues—or if heartwood rot could also be accelerated because of the fungus that woodpeckers transport to the tree.
“It’s nonetheless type of a wide-open query,” she says. “We steered two hypotheses: one is tree choice by the birds, that the birds are one way or the other choosing the timber based mostly on the presence of fungus, and the opposite is that birds are facilitating the motion of this fungus from tree to tree.”
Now a researcher on the Middle for Mycology Analysis, a part of the U.S. Forest Service, Jusino says she’s designing a brand new examine that goals to reply that query. She’s planning to begin the cultures this summer time, although because of the sluggish excavation habits of Crimson-cockaded Woodpeckers and sluggish progress of fungus it’s going to take a number of years to get outcomes.
Forests of the Future
As a stream of printed analysis provides to the understanding of woodpeckers as house builders in North American forests, an rising space of analysis is waiting for the essential function woodpeckers will play in forests of the longer term.
Wildfires and Woodpeckers
Local weather change and wildfires are drastically altering forest landscapes within the American West. In line with Andrew Stillman, a postdoctoral fellow on the Cornell Lab of Ornithology who research how chicken populations reply to fires, woodpeckers are a key to serving to forest communities get well after a fireplace.
“Wildfires usually create a pulse of lifeless or dying timber, adopted by a pulse of bugs that come to benefit from that lifeless wooden,” says Stillman. “The woodpeckers are following the bugs into the burned areas.”
Stillman says that when woodpeckers swarm right into a burn space filled with lifeless timber, they go proper to work excavating cavities: “And so the woodpeckers themselves then present a pulse of nest websites for lots of different species … like bluebirds, which eat a whole lot of berries and begin spreading seeds round these not too long ago burned locations.”
North Carolina State PhD candidate Lauren Pharr sees a few of the identical dynamics at play in her research on Crimson-cockaded Woodpeckers within the fire-prone longleaf pine forests of the Southeast, and she or he thinks the woodpeckers are offering greater than nesting houses—they’re offering shelters throughout excessive local weather occasions.
Throughout Pharr’s 4 years of learning red-cockaded nesting websites, she has famous a rise in extreme rain occasions within the North Carolina sandhills, and several other hurricanes within the Florida panhandle. She says Crimson-cockaded Woodpecker nest holes are serving to a menagerie of different cavity-dwelling species, from bluebirds and nuthatches to different woodpeckers like red-headed and red-bellied, to snakes, small mammals, even flying squirrels.
“That’s the most enjoyable factor on the market, climbing a tree after which a flying squirrel comes out, and it’s so cute to see him fly,” Pharr says. “It’s so spectacular.”
She says these cavities are vital for every kind of animals within the face of local weather change: “[Red-cockaded Woodpeckers] are mitigating stress for these different species. So in the event that they want a spot to go … in locations with excessive climate occasions or something like that, these cavities assist.”
Pharr’s recommendation for forest managers who need to optimize habitat for birds: Begin with ensuring a forest’s woodpeckers are taken care of.
“Crimson-cockaded Woodpecker itself is a extremely huge indicator species, and the administration that we do with Crimson-cockaded Woodpeckers additionally could be very helpful to different species in that ecosystem,” Pharr says. “So it’s a win-win.”
