a close look at those hard-working woodpeckers, with stephen shunk
WHEN I GOT my copy of the new “Peterson Reference Guide to Woodpeckers of North America,” I tracked down the author’s email address at once, and sent him a message:
“I’m mad for woodpeckers,” I wrote, and Stephen Shunk wrote back: “Mad for woodpeckers is a very good thing.”
I suspect if you are not already, that by the end of this story and podcast, you’ll be mad for them, too, and positively amazed at their physical capabilities and their critical role in our ecosystems.
Until I read his author bio, I felt lucky to live with six hardworking and highly entertaining woodpecker species here in my rural Northeastern garden. But Stephen, a longtime conservationist who also leads international woodpecker conservation tours, lives across the continent, on the eastern slopes of the Cascade Mountains in Bend, Oregon, in a spot that’s home to 11 breeding species. Jealous!
I welcomed Stephen Shunk to my weekly public-radio show and podcast to talk woodpeckers. Learn why most species are mainly black and white, and how they have evolved their anatomies to withstand all that hammering (which has been researched for insights to design football helmets, for instance).
Read along while you listen in using the player below, or at this link; it’s the June 20, 2016 edition of the program. And enter to win the book at the very bottom of the page, in the comments box.
my woodpecker q&a with stephen shunk
Q. Just to set the scene: How many woodpecker species are there worldwide, and in the United States?
A. It depends a little on who you ask, based on some differences in taxonomy. Basically there are about 200 woodpecker species around the world, and there are 23 for North America—north of Mexico.
A. That’s about right. The only exception would be the ivory-billed woodpecker, which may be extinct. But it’s nevertheless part of our North American avifauna, and it was a bit larger than the pileated. The book does cover those, but you’re right: The downy is one of the smallest woodpeckers in the world, and the pileated is one of the largest.
Q. I see most of my local species year-round, and suspect the yellow-bellied sapsucker is around, even if I don’t seem him as much in the warmer months in the garden. Are woodpeckers mostly non-migrants? [Below, yellow-bellied female.]
A. Most woodpeckers in the world are what we call sedentary—which does not mean they sit on the couch all day.
A. It means they don’t migrate. In North America, though, we have several migratory woodpecker species. Most of the sapsuckers are migratory, and the yellow-bellied sapsucker, which comes through your area, happens to be the most migratory woodpecker in the world.
Q. I didn’t know if he was just deeper in the woods or what—like with juncos, I don’t seem them in the summer much, but I think there are some nearby.
A. Most of the yellow-bellied sapsuckers breed across the Boreal Forest, the middle tier of Canada, but they breed all the way up as far as Eastern Alaska. Then they migrate down east of the Rockies, and go as far as Panama, and there are even a handful of records for Colombia.
Q. Wow; that’s a lot of territory. But most species are sedentary.
[Update: Steve and I checked the breeding maps for yellow-bellied sapsucker, and my precise location is just inside the breeding range, it turns out. I also checked my personal eBird data from past years, where I record birds I see in the garden, and I do in fact regularly record them both in February as well as May, during annual citizen-science counts. Cornell’s All About Birds says: “Although a few individuals remain throughout much of the winter in the southern part of the breeding range, most head farther south, going as far south as Panama.” Apparently I am in that “few individuals” area.]
A. Most of the woodpeckers are sedentary. So you see six species year-round in the East, and that would include the downy, hairy, flicker, red-bellied, red-headed and pileated.
Q. And I don’t see the red-headed where I am, but if I go an hour or so away I would see them more commonly.
A. That’s definitely a drive that’s worth it, a bird that’s worth seeing and driving for.
Q. I read in your new book that the woodpecker’s incredibly impact-withstanding physiology has inspired safer motorcycle and football helmets, and has even helped medical research on Shaken Baby Syndrome. What kind of force are we talking about?
A. This is probably one of the best examples of adaptation in the animal kingdom. Woodpeckers are definitely one of the most specialized bird families in the world.
When a woodpecker hits its head against a tree, it’s exerting about 1200 g’s of force. In order for us to do the same thing, we would have to hit our head against a brick wall going 16 miles an hour. So we would not survive that; it would be a very silly idea.
Back to the football and motorcycle helmets: When we have a motorcycle accident, or when we crash our head against another football player’s head—both of us wearing helmets—we are subjected to more g-force than we really should be exposed to.
I’m sure you’ve heard, especially in football, of the high incidence of brain injury. There is a lot of money spent trying to make football a safer sport, and so we study woodpeckers. Woodpeckers can do this—hammer their heads against trees with 1200 g’s of force—without getting any kind of injury, there is definitely something to be learned there. [Above, a downy tossing beakful of woodchips from a nest hole.]
Q. What are some of the woodpecker’s other secrets, the anatomical factors that help them withstand that impact?
A. One of the most important things is that woodpeckers have very little cerebrospinal fluid in their cranial cavity. In contrast, humans have a bit of cerebrospinal fluid that allows our brain to actually move a little bit inside there. This is what causes us to get concussions so easily.
When we hit our head in a traffic accident, our head gets slammed forward and our brain slams against the inside of our skull, because of that space in there known as subarachnoid space. Then it bounces back against the back of our skull, giving us what is called a contrecoups injury—we can get two concussions out of that.
The woodpecker has very little cerebrospinal fluid in the brain cavity, preventing the brain from sloshing around, and it also has sort of sponge-like bone in the frontal and occipital bones of the skull. It’s not spongy like a soft sponge, but it’s very low density and the bony fibers, I guess you could say, help disperse energy and thereby absorb shock.
And that’s just what’s inside the cranium. There is a whole suite of adaptations, including special ribs that other birds don’t possess, that allow strong muscle to attach to those ribs, and attach to the head and allow them to exert that level of force, and the reabsorbing the resultant forces and dispersing them down into the body, instead of into the head itself.
Woodpeckers that hammer their heads most frequently have broader base to their bills, which helps disperse force. They also have what’s called a frontal overhang, where the frontal bone actually bulges out a bit over the bill, and this allows the forces to be dispersed downward, away from the brain casing—instead of against the brain.
Q. And it’s not all about just the head; they have specialized feet, too. And even specialized extra-stiff tail feathers to stabilize them.
A. You bet. They have a special set of fused bones at the base of the backbone called the pygostyle, and this attaches to very strong muscles, which allows it to prop its tail against a tree. And like you said, those feet are amazing, and allow several of the species to live most of their lives in the vertical plane.
Q. I kind of never thought about that till I read it in your book. Birds, a lot of birds, are standing, so to speak—and these guys are often mostly vertical.
A. They’re hanging.
Q. And I love that they have built-in safety goggles to protect their eyes, too, don’t they?
A. Again, there are special muscles in there. The septum between the orbital sockets is thicker than most birds’, which allows special muscles to attach there and help protect the eyes.
And the nictitating membrane, sometimes called the third eyelid, which birds possess—in woodpeckers the nictitating membrane is thicker than most birds’, and allows them to protect their eyes when they’re hammering.
And there are two special organs in the woodpecker eyes called the pecten and the choroid. The instant before a woodpecker’s head contacts a hard surface, these two organs swell with blood and other fluids to increase the pressure inside the orbital socket and prevent the eye from moving forward.
Q. Wow, talk about prepared for the work at hand. Amazing. [Above, an excavation made by the pileated for feeding.]
Looking through the book, at the incredible photos you assembled from 70 photographers and other artists, I realize that most woodpeckers stick to a pretty strict dress code or color-palette. Why are so many woodpeckers mostly black and white?
A. We call that disruptive coloration. Since woodpeckers are generally found in forests and woodlands, those habitats have filtered light coming down through the canopy. This coloration, which we sometimes call pied coloration of speckled and striped black and white, allows them to be a little more camouflaged inside the canopy.
Q. Oh, so it’s to work with the nature of the light inside the forest—interesting.
A. Exactly. And if you look at the black-backed woodpecker that occurs across the boreal forests but also down into the Black Hills of South Dakota and also where I am in the West, in the Cascade Mountains and the Sierra Nevada, this bird spend a lot of its time in burned forests. When it’s propped up against a burned tree, it’s very difficult to see.
Q. Very smart—and it leads to my next question. I’m a person who wants to know how all the puzzle pieces outside fit together: who eats who or what, who coevolved with who or what to what end game, etc. What I think I loved reading about most of all in your book was the notion of woodpeckers as keystone species.
A. Keystone species are fascinating organisms. If you think about an arch made of stone, the keystone of course is the one at the center, at the top of the arch. Removing that stone causes the arch to collapse.
Keystone organisms in an ecosystem, they behave very similarly. If those organisms are removed, that places that ecosystem in jeopardy to varying levels of extent. The other way to describe it is that woodpeckers in general may not represent a large amount of the biomass in an ecosystem, but they have a disproportionately large impact on other organisms in that habitat.
The Number 1 keystone role played by woodpeckers is the excavation of their nest cavities. All woodpeckers nest in cavities every year. Most woodpeckers excavate new cavities each year. And most woodpeckers roost in nest cavities at night year-round—so they’re constantly excavating these cavities.
There are over 40 species of birds alone, not including the woodpeckers, that also nest in woodpecker cavities in North America.
Q. Who can’t create them.
A. Exactly. We call them secondary cavity nesters, and they depend entirely on woodpeckers to excavate these cavities for them.
Q. In this keystone role there are other animals, insects, etc. who take advantage of the work that woodpeckers do. [Above, Red-spotted Purple butterfly feeding at sapsucker sap wells.]
A. You bet. In your area there’s a great example, because the ruby-throated hummingbird is a long-distance migrant, and it follows the yellow-bellied sapsucker northward in migration. And this occurs often before there are many flowers blooming, so how does that hummingbird eat?
Well, it does eat insects, but it also will feed at the sap wells of the yellow-bellied sapsucker.
Q. And the way I learned about that, Steve, was not a happy one for a gardener. [Laughter.] I learned about it when I first saw those diabolically symmetrical sapsucker wells—the holes it was making in one of my favorite ornamental trees. But I read up, and that this role was benefiting the ruby-throated hummingbird, and I thought: I have to let it go; I just have to be OK with this. [Above, Anna’s hummingbird feeding at sap wells; photo by Laura Osteen.]
Q. This is part of a whole big cycle that’s bigger than me. It’s quite amazing what they do—they open up these sap wells.
A. And the sap leaks out, and they are specially adapted to eating that sap year-round, although they will eat insects, and they will even eat insects who are attracted to the sap. Their adaptations are designed to make them sap eaters.
It’s important to note that the yellow-bellied sapsucker used to have a very bad reputation for doing just what you described, excavating sap well and causing these scars in timber plantations all across the United States.
It was really seen as a bad thing, and it was a bad thing for woodpeckers—they all got a bad name. Until there was some research done to show that these woodpeckers actually have a much greater positive role than negative role.
You can rest assured that most of the time when a sapsucker makes rings around a tree, it might have an aesthetic impact, but rarely does it cause physical long-term harm to the tree. Trees that are not native to the United States may not fare as well as natives. The ones that are native evolved with the sapsucker.
Q. Yes, the ornamental, gardener-type plants—like I have some deciduous Asian magnolias, and in the Northeast, the yellow-bellieds love magnolias. Who knows why; they just do. And it’s just one of those thing.
How do they even pick the right tree? To make sap wells in, to live in—to roost, to nest. How do I know what a good tree is if I’m a woodpecker. [Above, hairy woodpecker nestling in a nest hole.]
A. There are two different answers to that question. If it’s a sapsucker, they need a live tree, of course—a tree that’s going to be producing sap. They will often choose whatever tree has the thinnest bark, and is therefore easiest to tap.
More important is the other part of the answer, which is how do woodpeckers decide where to excavate their nest cavity. We’ve had a profound impact on our landscape that has affected woodpeckers and all cavity nesters. This habit that we have is the removal of dead tree, or standing snags, from the landscape.
To some extent, it’s understandable; we needed to remove snags because they were seen as unattractive, and they can pose a safety threat.
But removing all the snags is not a healthy thing for any woodland or forest. All these treed areas should have what we call “a broad succession of age classes,” meaning seedlings, saplings, small medium and large trees, dying trees and dead trees. That’s what a healthy forest includes.
Woodpeckers will traditionally choose dead and dying trees to excavate their cavities. It’s very important that if we’re going to cut dead trees down, we don’t need to cut them at the bases. We can cut them even as low as 5 or 10 feet, and they can still provide a tremendous amount of benefit for cavity-dwelling life.
Q. I’ll say as a gardener that I have a great snag that I created—a tree whose crown was deteriorating and posing some potential damage to an outbuilding. So I topped it, and left it as a snag, and boy, it just brings me so much enjoyment. The wildlife interaction that goes on in that tree, and not just birds! It’s a wonderful thing—plus the biomass that it represents, food for so many creatures, some of which are too small for us to even see…and then larger animals eat them.
I’m a lover of snags over here. [Laughter.] [Above, a snag in Margaret’s garden.]
So that’s how they pick a tree for excavating a cavity—they’re looking for a tree that’s dying or dead.
A. That’s the preference, but several woodpeckers will excavate in live trees, if they have heart rot. That means they only have to get through a relatively thin wood layer of on the outside of the tree and they they’re gotten through the rotten material on the inside—which makes it very easy to excavate.
Q. I have to say the flicker is one of the most beautiful birds, if people really look at its patterns and colors. Who’s your favorite aesthetically? [Above, a Northern red-shafted flicker with its extraordinary tongue extended.]
A. I like the flicker a lot, but my favorite I think is the Lewis’s woodpecker. This is the Western equivalent of the red-headed; they’re very closely related. This is the only green woodpecker in North America, and it has this beautiful rosy-pinkish-red breast, and red in the face, and this silver collar. Also ironically it and the flicker are probably the least woodpecker-like of all American woodpeckers.
The Lewis’s [below] is a fly-catching woodpecker; he has special adaptations for catching aerial insects. And the flicker is an anteater, who spends most of his time on the ground-eating ants.
Q. I love when they are doing that.
A. They’re fun to watch.
more from stephen shunk
enter to win the new woodpecker guide
I’LL BUY A COPY of “Peterson Reference Guide to Woodpeckers” by Stephen Shunk for one lucky reader. All you have to do to enter is answer this question in the comments box at the very bottom of the page, below the last reader comment:
What woodpeckers visit your garden? Was there some fact in this interview that was a real “aha” for you about these hard-working birds?
No answer, or feeling shy? Just say something like, “Count me in,” and I will–but answer is even better.
I’ll select one random winner after entries close at midnight Monday, June 27, 2016. US only. Good luck to all.
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